FIELD GUIDE FOR INSPECTION, EVALUATION, AND …

AIR FORCE HANDBOOK

32-1282 VOLUME 1 1 JULY 1999

FIELD GUIDE FOR INSPECTION,

EVALUATION, AND MAINTENANCE CRITERIA

FOR ELECTRICAL SUBSTATIONS AND

SWITCHGEAR

DEPARTMENT OF THE AIR FORCE

THIS PUBLICATION CONTAINS COPYRIGHTED MATERIAL

Downloaded from http://www.everyspec.com

AFH 32-1282V1

BY ORDER OF THE AIR FORCE HANDBOOK 32-1282V1 SECRETARY OF THE AIR FORCE 1 JULY 1999

Civil Engineering

Field Guide for Inspection, Evaluation and Maintenance

Criteria for Electrical Substations and Switchgear

This handbook summarizes procedures and guidance to Air Force electricians for the inspection, evaluation, and maintenance of substations, switchgear, and associated devices. It will also assist maintenance engineers and

quality assurance evaluators in specifying and inspecting contractor performance. Contents

Chapter 1 Overview of the Guide 1-1 Scope............................................................. 1 1-2 Supplementary Information ........................... 8 1-3 Basis for Developing Field Procedures ......... 9 1-4 Preinspection Procedures ............................. 10

Table 1-1 Equipment covered in this handbook.... 1 Table 1-2 Equipment covered in AFH 32-1282V2 8

OPR: HQ AFCESA/CEOM (Capt Thomas E. Wahl) Certified by: HQ AFCESA/CEO (Col William R. Pearson) Pages 110/Distribution F

THIS PUBLICATION CONTAINS COPYRIGHTED MATERIAL


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Index AFH 32-1282V1

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Chapter 2. General Substation Guidance 2-1 Use of Substation One-Line Diagrams.......... 16 2-2 Operating Information.................................... 20

Table 2-1 Installation electrical one-line diagram deficiencies....................... 21 Table 2-2 Safety electrical one-line diagram features........................................... 22

Chapter 3. Substation Support Elements 3-1 Substation Tests............................................ 23 3-2 Substation Support Elements EPM Reports . 26

Table 3-1 Recommended maintenance based in IR temperature rises ................... 24 Table 3-2 Maximum acceptable ground resistances ..................................... 25 Table 3-3 Substation support elements general data ................................... 26 Table 3-4 EPM column headings.......................... 29 Table 3-5 Substation support element readings or test values ................... 29 Table 3-6 Substation support element checks...... 30


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Index AFH 32-1282V1

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Chapter 4. Circuit Breaker Performance 4-1 Circuit Breaker Basics ................................... 31 4-2 Circuit Breaker Conducting Contacts and Arc Extinguishing Processes .......................... 32 4-3 Circuit Breaker Operating Mechanisms......... 35 4-4 Circuit Breaker Elementary Diagrams ........... 40 4-5 Circuit Breaker Nameplates........................... 43

Table 4-1 Circuit breaker normal ratings............... 32 Table 4-2 Circuit breaker stored energy methods. 36 Table 4-3 Low-voltage circuit breaker minimum nameplate information.................... 43 Table 4-4 Medium and high voltage circuit breaker minimum nameplate information .... 45

Chapter 5. Circuit Breaker Testing 5-1 De-Energized Circuit Breaker General Tests 48 5-2 De-Energized Tests Specific to the Circuit Breaker Type ............................................ 52

Table 5-1 Circuit breaker insulation-resistance test values ............................................. 49

Chapter 6. Circuit Breaker Evaluations 6-1 Circuit Breaker EPM Reports ........................ 53 6-2 High-Voltage SF6 or Oil Insulated Circuit Breakers.................................................. 54 6-3 Medium-Voltage Vacuum or Air Insulated Metal-Clad Switchgear Circuit Breakers . 56 6-4 Low-Voltage Circuit Breakers........................ 60

Table 6-1 Circuit breaker general data ................. 53 Table 6-2 Circuit breaker readings or test values . 54 Table 6-3 External high-voltage circuit breaker checks ............................................ 55 Table 6-4 Internal high-voltage circuit breaker tank procedures and checks .......... 56 Table 6-5 Medium-voltage metal clad switchgear circuit breaker checks..................... 59 Table 6-6 Low-voltage circuit breaker checks....... 60


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Chapter 7. Interrupter Switch Installations 7-1 Interrupter Switch Basics............................... 63 7-2 Interrupter Switch Operating Features .......... 67 7-3 Interrupter Switch De-Energized Device Tests ....................................................... 71 7-4 Interrupter Switch EPM Reports.................... 72

Table 7-1 Interrupter switch ratings ...................... 64 Table 7-2 Fuse ratings .......................................... 65 Table 7-3 Interrupter switch minimum nameplate information...................................... 66 Table 7-4 Fuse minimum nameplate information.. 67 Table 7-5 Interrupter switch test requirements ..... 72 Table 7-6 Interrupter switch general data ............. 72 Table 7-7 Interrupter switch checks ...................... 73

Chapter 8. Switchgear and Switchboard Assemblies 8-1 Assembly Performance ................................. 74 8-2 De-Energized Assembly Tests ...................... 81 8-3 Energized Assembly Tests ............................ 81 8-4 Assembly EPM Reports................................. 82

Table 8-1 Industry classification for assemblies ... 79 Table 8-2 MC/MEI switchgear major differences.. 80 Table 8-3 Assembly test requirements ................. 81 Table 8-4 Assembly general data ......................... 83 Table 8-5 Assembly checks .................................. 84


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Chapter 9. Battery Installation 9-1 Battery Installation Basics ............................. 85 9-2 Battery Installation Readings and Tests........ 89 9-3 Battery Installation EPM Reports .................. 93

Table 9-1 Battery installation readings.................. 90 Table 9-2 Capacity test procedures ...................... 92 Table 9-3 Battery capacity degradation ................ 92 Table 9-4 Integrity test procedures ....................... 93 Table 9-5 Battery installation general data ........... 94 Table 9-6 Lead-acid battery installation corrective actions ............................................ 95 Table 9-7 Nickel-cadmium battery installation corrective actions ........................... 96 Table 9-8 Battery installation checks .................... 96

Chapter 10. Protective Sensing, Processing, and Action Devices 10-1 Device Performance ...................................... 97 10-2 Device Testing............................................... 99 10-3 Installation-Wide Operating Systems ............ 102 10-4 Protective Sensing, Processing, and Action Device EPM Reports.................... 102

Table 10-1 Relay tests ............................................ 100 Table 10-2 Relay pickup parameters ...................... 101 Table 10-3 Device general data.............................. 102 Table 10-4 Instrument, metering and protective relay general checks ............................... 105


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Acknowledgment

The Air Force wishes to express their sincere appreciation to the many companies and their representatives who kindly cooperated in supplying CAD illustration inputs and pictures for use in this handbook. Inputs used for CAD illustration inputs were supplied by Siemens Energy and Automation, Inc.; Square D Company/Groupe Schneider; and Westinghouse/Cutler Hammer. Some pictures were supplied by Keller & Gannon. The Air Force expresses particular appreciation to Williams Learning Network (formerly NUS Training Corporation) whose training videos were used to provide the rest of the pictures.

NOTE: Product and manufacturer names are included in this handbook for the purposes of illustration and do not carry the specific endorsement of the Air Force.


AFH 32-1282V1

Chapter 1. Overview of the Guide AFH 32-1282V1

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CHAPTER 1. OVERVIEW OF THE GUIDE 1-1. Scope. The condition of electrical power apparatus found in substations is crucial to the successful operation of all electrical power systems. Switchgear and related equipment are significant components of the systems. This handbook identifies field procedures which allow early detection of equipment degradation and other defects which will adversely affect reliability. Appropriate corrective actions can then be accomplished.

a. General Categories of Substation Equipment. Table 1-1 lists the general categories of substation equipment covered in this Air Force maintenance handbook. Figures 1-1, 1-2, 1-3, 1-4, 1-5, and 1-6 have been provided to remind the technician of similar and differing features of various circuit breaker and switchgear types. Substation equipment categories discussed in AFH 32-1282V2 (Field Guide for Inspection, Evaluation, and Maintenance Criteria for Electrical Transformers) are listed in Table 1-2.

Table 1-1. Equipment covered in this handbook Substation support elements providing area safety Transmission/distribution power-line switching

! Circuit breakers ! Load interrupter switches

Power-line switching unit/assembly necessary sub-elements ! Switchgear/switchboard assemblies

! Battery installations ! Protective sensing, processing, and action devices


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5

74

3 6

2

1

1. Interrupters 2. Bushings 3. Control cabinet 4. Pressure gauges and operation counter 5. Current transformers 6. Steel base 7. Base legs

Figure 1-1 High-voltage SF6-gas-insulated circuit breakers


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5

4

3

21

1. Compressor 2. Pull rod 3. Control panel 4. Mechanism 5. Reservoir 6. Bushing 7. Oil level indicator 8. Oil vent 9. Tank 10. Mechanism housing11. Local control

11

9

6

7

8

10

Figure 1-2 High-voltage oil-insulated circuit breakers


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23

1

54

6

10987 1. Relays 2. Switches 3. Instruments/meters 4. Compartment barriers 5. Circuit breaker wheels 6. Circuit breaker rails 7. Drawout circuit breaker 8. Circuit breaker mechanism 9. Barriers 10. Automatic shutters

Figure 1-3 Medium-voltage metal-clad vacuum circuit breaker switchgear


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5

2

3

4

2

7

6

9

8

1. Switch operator 2. Padlock location 3. Inspection window 4. Main door 5. Door stop 6. Safety barrier 7. Door interlock 8. Switch interlock 9. Barriers 10. Switch position indicator11. Padlock location 12. Key interlocks 13. Operating handle 14. Nameplates

71

Figure 1-4

Medium-voltage metal-enclosed load-interrupter switchgear

1312141011

12


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1 2 31. Finger clusters 2. Extension rail 3. Levering arm 4. Moving contacts 5. Stationary contacts 6. Molded base 7. Arcing contact spring

7

5

4

110

9

6

8

8. Stationary arcing contact 9. Moving arcing contact 10. Insulation link

16 1415

1312

1111. Pole unit 12. Interface barriers 13. Secondary disconnect contacts 14. Levering device arm

19

17

18

15. Main disconnect contacts16. Sensors 17. Drawout circuit breaker 18. Switchgear 19. Rail mounted lifter

Figure 1-5 Low-voltage air circuit breaker switchgear


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1

6

2

5

4

8

9

7

3

1. Main circuit breaker 2. Group-mounted circuit breakers 3. Vertical bus behind 4. Hinged wiring access panels 5. Side access panel 6. Removable cover plates 7. Ventilation grille 8. Blank filler plates 9. Warning and manufacturer’s labels

Figure 1-6 Low-voltage molded-case circuit breaker switchboard


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Table 1-2. Equipment covered in AFH 32-1282V2 Power/distribution transformers Instrument transformers

Bushings Surge arresters

b. Purpose. Equipment deterioration needs to be identified before the equipment malfunctions or fails (that is, preventative maintenance). This handbook allows local preparation of electrical preventative maintenance (EPM) procedures. It does not cover catastrophic or operational failures. Its purpose is to prevent equipment failures resulting from a lack of proper preventative maintenance.

c. Technician Testing Limitations. The handbook is not a training guide. Air Force technicians should not use testing/metering/scanning devices around or on energized equipment unless they have been trained in their use and have satisfactorily demonstrated their knowledge of appropriate safety precautions. 1-2. Supplementary Information. The maintenance technician should be familiar with and have available Air Force electrical design, maintenance, and safety manuals.

a. Design. Refer to the installation requirements of AFMAN 32-1180(I) (Electrical Power Supply and Distribution) which provides Air Force policy and guidance for design criteria and standards for electrical power supply and distribution systems.

b. Maintenance. Refer to AFMAN 32-1280(I) (Facilities Engineering, Electrical Exterior Facilities) which amplifies the maintenance and repair guidance of this handbook.


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c. Safety. Refer to AFMAN 32-1185 (Electrical Safe Practices) which provides safety standards for the work being done. Maintenance work should be done only by workers in accordance with the electrical work classifications of AFMAN 32-1185, including AFSC 3E011 equivalent (helper), AFSC 3E031 equivalent (apprentice), AFSC 3E051 equivalent (journeyman), or AFSC 3E071 equivalent (craftsman). AFH 32-1285 (Electrical Worker Safety Field Guide) should be available to you to use in the field. 1-3. Basis for Developing Field Procedures. This handbook is intended as summary guidelines and procedures. Actual maintenance/repair program requirements should be adjusted as appropriate for your specific electrical apparatus.

a. Handbook Information. This handbook covers generic apparatus performance, test data, and generally applicable component element checks. Use this handbook as a reminder of general maintenance requirements.

(1) Performance. Each component of major electrical apparatus performs essentially a simple operation. Complexity in maintenance is caused by the large and varied types of electrical components in the apparatus. This handbook provides figures and pictures to illustrate the most important of these components.

(2) Tests. Electrical equipment must be tested to ensure its continuing operating capability.


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(a) Test Descriptions. Descriptions of the most commonly used tests are included in this handbook. Acceptable values of the tests are provided when possible. Reference to the manufacturer’s literature may be required for other tests.

(b) Comparisons for Trends. All tests/readings should be compared to previous values (acceptance, maintenance, or repair). This will assist in recognizing trends that indicate a need for more frequent testing. Permanent changes to equipment/devices that are overloaded, misapplied, or inadequate for the duty to which they are subjected may be required.

(3) Component Element Checks. Tables are included in this handbook which outline the most important components to be checked. Additional information on these components can be found in AFMAN 32-1280(I) and the manufacturer’s literature.

b. Locally Developed Field Procedures. Each facility should maintain a copy of all applicable documents related to the installation, operation, and maintenance of electrical systems. Locally developed EPM procedures are essential to proper maintenance. 1-4. Preinspection Procedures. Prior to performing any field work, review historical EPM data and applicable safety requirements.

a. Apparatus Documentation. Assemble all documentation applying to the apparatus to be checked.


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(1) Documentation Maintenance. The Base Civil Engineer (BCE) should ensure all documentation is maintained for each specific item of electrical apparatus which makes up the facility electrical power systems.

(a) Available From Design/Construction Files. The available data may include all of the inspection and testing procedures for the facility, copies of previous reports, single-line diagrams, schematic diagrams, electrical equipment plans, records of complete nameplate data, and manufacturer’s service manuals and instructions.

(b) Locally Prepared. Prepare local EPM forms as necessary for installed equipment. Each item of apparatus should be shown on an equipment location plan. (See Paragraphs 3-2, 5-1, 6-1, 7-4, 8-4, 9-3, and 10-4). Provide unique apparatus designations along with a locally prepared safety electrical one-line diagram and equipment location plan. Table 2-2 summarizes the minimum recommended features of a safety electrical one-line diagram.

(2) Specific Assembling of Data: Assemble the following data, if available, for each specific item of apparatus.

! Locally prepared forms. ! As-built drawings for electric equipment layouts and elevations. ! Trend analysis data which should include:

(a) Installation acceptance data test results. (b) Previous EPM reports including any previous systematic evaluations.


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! Manufacturer’s service manuals including practices and procedures for: (a) Installation. (b) Disassembly/assembly (interconnection). (c) Wiring diagrams, schematics, bills of materials (d) Operation (set-up and adjustment) (e) Maintenance (including parts list and recommended spares) ( f ) Software programs. (g) Troubleshooting guidance.

(3) Systematic Evaluation of Apparatus Condition. Electric apparatus should receive a systematic evaluation of its condition after an EPM which indicates repairs were necessary beyond normal expected maintenance. The systematic evaluation should include:

! Reasons for the required repairs. ! Work required to complete the repairs. ! Assessment of the remaining service life. ! Determination of the need for a more frequent EPM.

c. Safety Requirements. Working on or near normally energized lines or parts requires observance of rules applying to safe working distances, work methods related to whether the line has been de-energized or left hot, and recognition of work hazards which require more than one worker for safety. Workers must be qualified for the work and use approved work methods and equipment. Refer to the requirements of AFH 32-1285 as amplified by AFMAN 32-1185. Always include a tailgate meeting to address existing site conditions and the procedures to be followed. Work will be done de-energized unless energized line work is specifically authorized.


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(1) De-Energized Electrical Line Work. Follow the safe clearance (lockout/tagout) procedures given in AFH 32-1285. Remember lines are considered energized if the de-energized systems have not been provided with proper protective grounding. The safe clearance may require a job hazard analysis.

(2) Energized Electrical Line Work. Work on energized lines and equipment only when authorized by the electrical supervisor/foreman/lead electrician (per local organization) based on the need to support a critical mission, to prevent injury to persons, or to protect property. Insulating means must be provided to isolate workers from a source of potential difference. A job hazard analysis is required for energized line work. (See AFH 32-1285).

d. Understanding Maintenance Frequencies. Frequency of maintenance should be locally adjusted based on the application of the equipment. See additional guidance in NFPA 70B (Electrical Equipment Maintenance). Adjust the frequency of inspection based on the criticality of the apparatus, the severity of the loading conditions, and an environment where unusual service conditions stress the equipment. Generally, usual service conditions extend only to elevations of not more than 3,300 feet (1 kilometer) and ambient temperatures of no more than 30 to 40 degrees C. Check with the manufacturer for other than normal service conditions.

e. Inspection Materials/Devices. Basic items needed for an EPM include the following: ! A facility electrical truck ! Available documentation. ! EPM forms. ! Directions as to any input or approval needed from the appropriate using or

operating agency


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! Test equipment such as an (1) Automatic insulation test set (2) Dielectric test set (3) Digital ground resistance test set (4) Fault gas analyzer (5) Infrared imager (6) Circuit breaker test set (7) Corona tester

(8) Motion analyzer (9) Null balance (megohmmeter) earth

test set (Megger7) (10) Power factor test set (11) True root-mean-square (rms) digital

multi-electrical parameters meter (12) SF6 gas moisture analyzer

! Measurement instruments and miscellaneous devices such as a (1) Cycle counter or timer (2) Digital thermometer (3) Multirange ac and dc voltmeters and

ammeters

(4) Multirange noninductive load resister (5) Phase shifter (6) Phase angle meter (7) Three-phase sequence indicator

! Contamination washing devices such as a portable nozzle washer truck ! Miscellaneous tools such as

(1) Binoculars (2) Flashlights (insulated) (3) Insulated fuse puller (4) Magnifying glass

(5) Tape recorder, tape, and batteries (6) Video camera and accessories (7) Oil sample bottle and syringes and

gas sample bottles


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! Cleaning devices

(1) Vacuum cleaner (2) Compressed air cleaner (not for use in medium or high voltage enclosures

or other locations where dust could cause flashover) ! Miscellaneous materials as necessary to clean, wipe, paint, insulate, solder, or for

other small field-fix repairs.


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Chapter 2. General Substation Guidance AFH 32-1282V1

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CHAPTER 2. GENERAL SUBSTATION GUIDANCE 2-1. Use of Substation One-Line Diagrams. A substation is an area or an equipment group which contains switches, circuit breakers, buses, and transformers. It provides for the switching of power circuits and for the transforming of electrical power from one voltage to another or from one system to another. Stations without transformers are more properly called switching stations, but for simplicity the word substation will be used to include switching stations.

a. Determine System’s Circuit Arrangement. A system is designed to meet load requirements, reliability, and flexibility. The criticality of the load also means maintainability must be considered.

b. Basic Circuit Arrangements. Various common distribution systems are shown on Figures 2-1, 2-2, 2-3, 2-4, 2-5, and 2-6. Understanding how your facility’s distribution system is configured is the key to providing safe clearing or isolating procedures for any portion of the system needing maintenance and repair. Figure 2-1 is the simplest circuit arrangement. This simple system provides no backup reliability and loads cannot be backfed as is the case with Figure 2-2. Selective systems (Figures 2-3 and 2-4) provide alternate sources of input power. Network systems (Figures 2-5 and 2-6) provide the ultimate in service reliability.


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LOAD CIRCUITS

MAIN DISTRIBUTION BOARD

LOAD UNITS

SOURCE OFSUPPLY

TRANSFORMER

CIRCUIT BREAKERFEEDER

SOURCE OFSUPPLY

CIRCUIT BREAKERLOADCENTER

DISCONNECTSWITCH

LOOPPRIMARYFEEDERLOAD CIRCUITS

TRANSFORMER

Figure 2-1 Radial system

Figure 2-2 Primary loop system


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LOAD CIRCUITS

TRANSFORMER LOAD CENTER

CIRCUIT BREAKER

SOURCE OFSUPPLY

PRIMARYFEEDERS

TO OTHER LOADS

SELECTIVESWITCH

TO OTHER

LOADS

TRANSFORMER

LOAD CIRCUITS

DISCONNECTSWITCH

PRIMARYFEEDERS

CIRCUIT BREAKER

SOURCE OFSUPPLY

Figure 2-3

Primary selective system Figure 2-4

Secondary selective system


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TRANSFORMERCIRCUIT BREAKER

LOADCENTERS

NETWORKPROTECTOR

DISCONNECTSWITCH

LOAD CIRCUITS

PRIMARYFEEDERS

NETWORKPROTECTOR

SOURCE OFSUPPLY

SOURCE OFSUPPLY

CIRCUIT BREAKER

LOADCENTERS

NETWORKPROTECTOR

PRIMARYFEEDERS

LIMITERLUGS

SECONDARY TIES

LOADCIRCUITS

TRANSFORMERDISCONNECTSWITCHES

Figure 2-5 Spot network system

Figure 2-6 Distributed network system


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2-2. Operating Information. For maintenance to be done safely, operating information must define energy paths and switching control components. Each component should be provided with a unique identification and a specific location.

a. One-Line Diagram Preparation. As a part of the Apparatus Documentation (see Paragraph 1-4) each installation should prepare safety electrical one-line diagrams. Develop safety electrical one-line diagrams from the installation electrical one-line diagrams. Installation electrical one-line diagrams are design documents made for construction and contain unnecessary installation data. Safety electrical one-line diagrams should be prepared by facility personnel and should show only data relevant to safe operating procedures. Table 2-1 indicates installation electrical one-line diagram deficiencies that make this document a poor substitute for a safety electrical one-line diagram. Installation electrical one-line diagrams may still need to be consulted for design information for replacements. Table 2-2 summarizes the minimum recommended features of safety electrical one-line diagram

b. Equipment Location Plan Preparation. As a part of the Apparatus Documentation (see Paragraph 1-4) each installation should prepare a simplified electric equipment layout corresponding to the safety electrical one-line diagram. The plan should locate all the components shown on the safety electrical one-line diagram using the same identification. Also show power circuit routing which cannot be observed at the site.


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Table 2-1. Installation electrical one-line diagram deficiencies Inaccuracies

Generally not correct due to electrical system changes.

Illegibility Generally not designed for field service under poor lighting conditions. Drawings may be faded with small lettering and close linework obscuring safe switching (isolation) requirements.

Distinctive Identification A unique component identification is not provided. Drawings may indicate only one apparatus item or switchgear section while other items or sections are noted to be similar.

Unessential Safety Data Design data such as instrument transformer ratios, surge arrester ratings, and other design information only complicates understanding safety requirements.1 1This information should be covered by the EPM apparatus documentation.


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Table 2-2. Safety electrical one-line diagram features

Correctness Diagrams must be kept up to date, otherwise they are useless.

Clarity Diagrams should ensure that lines are heavy, at least a 1/4-inch (6.5-millimeters) apart, with printing at least a 1/4-inch (6.5-millimeters) high, preferably done by computer-aided design (CAD). The drawings will be used under less than desirable conditions so prepare them on the number of sheets necessary to provide legibility, manageability, and durability.

Component Identification Each component must have a unique identification shown on the diagram and placed on each component. Identification means on the actual component must be durable and large enough to be read at a distance. Place as often as necessary so that there is no question as to the component being identified. Short alphanumeric designations are better than operating names. Avoid geographic descriptions. Do not put special warnings on the identification means.

Components Shown The components to be shown on a diagram are all sources of electrical energy, the devices that can interrupt this energy, and other major components such as power conductors, power/distribution and instrument transformers, surge arresters, capacitors, automatic controls, interlocks, and loads.


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Chapter 3. Substation Support Elements AFH 32-1282V1

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CHAPTER 3. SUBSTATION SUPPORT ELEMENTS 3-1. Substation Tests. Tests of support elements are generally limited to infrared tests on connections and grounding resistance tests on permanent ground systems.

a. Infrared (Thermographic) Testing. An infrared (IR) temperature measurement locates high-resistance or hot spot thermal variations due to component failure, fatigue, and mechanical misalignment.

(1) Precautions. The object being examined will radiate both emitted and reflected IR energy. Only the emitted IR energy is a measure of the object’s temperature. Measurements will vary as the geometry of observation varies the angle of incidence. Changing the angle of incidence changes the reflected IR energy. The IR equipment used should be capable of detecting at least a 1 degree C temperature difference between the object and the 30 degree C reference area by detecting emitted radiation and converting it to a visual signal. The IR equipment should allow the user to mathematically compensate for reflected energy. Correction may be made by entering an estimated emmissivity value provided by the IR equipment manufacturer or based in the installation’s experience.

(2) Action. Scan all current-carrying equipment and conductor connections during periods of maximum possible loading. Generally a reading for an equipment/conductor load below 40 percent of its rating will not locate any hot spots. Always measure the IR temperature from several different positions to minimize the chance of error from reflected IR energy or from solar gain for outdoor installations.


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(3) Interpretation. Infrared hot-spot temperature gradients indicating possible deficiencies are given in AFMAN 32-1280(I) for equipment. Table 3-1 lists temperature rises above ambient which have been found practical in regard to equipment problems.

Table 3-1. Recommended maintenance based on IR temperature rises Temperature rise

above ambient (degrees C)

Recommendation

<10 Repair in regular maintenance schedule; little probability of physical damage. 10-39 Repair in near future. Inspect for physical damage. 40-75 Repair in the immediate future. Disassemble and check for probable damage. >75 Critical problem; repair immediately

b. Permanent Ground System Resistance Tests. A ground resistance test set can be used to determine the effectiveness and integrity of the grounding system. See AFMAN 32-1280(I) and AFMAN 32-1185 for the importance of adequate grounding in operating and maintaining electrical systems safely.

(1) Precautions. Testings of grounds can create hazardous conditions as all electrical conductive paths for overvoltage and fault currents are connected to the substation ground system. Rubber gloves, blankets, and other protective devices are recommended.


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(2) Action. Measure the ground path resistance of all branches of the grounding system from ground connections at support structure, equipment enclosures, and neutral conductors to the ground system. Measure other resistances covered in Table 3-2 which indicates maximum acceptable ground resistances.

Table 3-2. Maximum acceptable ground resistances Resistances Measured 1 to 25 ohms1 Substation

0.5 ohm Gates and gateposts2 0.5 ohm Operating rods and handles of group operated

switches and their supporting structures 1In accordance with departmental standards. 2Measurement of flexible gate ground connection adequacy.

(3) Recommendations. Where no departmental standards are available it is recommended that substations of 1,000 kVA or less have a maximum ground resistance of 5 ohms and substations over 1,000 kVA have a maximum ground resistance of 3 ohms.

c. Corona. Check for corona as covered in Paragraph 8-3.


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3-2. Substation Support Elements EPM Reports. Each installation should prepare local blank EPM report forms to be filled out by the inspecting technicians. (See Paragraph 1-4). The following tables indicate the data to be recorded.

a. Basic Substation Support Elements Information to Be Determined Before the Inspection. Provide a suitable record header with blank spaces for insertion of the following data given in Table 3-3. Pictures 3-1, 3-2, 3-3, and 3-4 show actual substation support elements.

Table 3-3. Substation support elements general data1 General Type

Designation Date of inspection

Location Single line diagram drawing no(s)

Equipment location plan drawing no(s) System voltages and design kVA

Approximate area Year installed

Last inspection date

Switching only High- to medium-voltage Medium- to low-voltage

Aerial service Underground service

1For guidance on EPM reports covering bushings, instrument transformers, and surge arresters see AFH 32-1282V2.


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Picture 3-1 Low-profile substation

Picture 3-2 Bus structure


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Picture 3-3 Circuit

breaker bay

Picture 3-4

Transformer bays and secondary underground line structures


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b. Basic Inspection Items to be Checked. Provide an EPM inspection report with column headings covering items to be checked off for each listed item number given in Table 3-4.

Table 3-4. EPM column headings Item no. (for easy referral)

Inspection item (name) Operating mode (in-service or de-energized

and grounded)

Passing criteria (list) Inspection method (visual, test, or other)

Corrective action (if necessary)

c. Inspection Items to be Covered. List inspection items to be covered. Table 3-5 indicates substation support element readings or test values and appropriate evaluation paragraphs for passing criteria. Table 3-6 indicates substation support element components and appropriate inspection actions.

Table 3-5. Substation support element readings or test values Readings or test values Evaluation reference paragraph

1. Ambient temperature -- 2. Infrared temperature rise 3-1a1 3. Ground resistance 3-1b1 1Readings should identify location or be provided with such identification in a separate report.


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Table 3-6. Substation support element checks 1. Fences and support structures a. Structural (security)

integrity b. Grounding c. Surface condition 2. Yards a. Adequate warning signs b. Acceptable surface

treatment c. General housekeeping d. Workable lighting system e. Environment compliance 3. Insulators and air disconnect

switches a. Fractures b. Contamination

4. Buildings a. General housekeeping b. Lighting c. Ventilation d. Heaters e. Structure condition f. Fire protection 6. Capacitors a. Operable fuses b. Operable internal resistors c. Verify automatic operation d. Test and reading per

AFMAN 32-1180(I) 7. Electrical connections and buses a. Tightness b. Hot spots c. Contamination

d. Corrective Action. Describe corrective actions taken. Deficiencies requiring action beyond the technicians at the site should be indicated as “see note X.” “Note X” should explain reasons. Such a note might indicate that an aerial bus, insulators, and air disconnect switches need suitable washing to eliminate excessive contamination.


AFH 32-1282V1

Chapter 4. Circuit Breaker Performance AFH 32-1282V1

32

CHAPTER 4. CIRCUIT BREAKER PERFORMANCE 4-1. Circuit Breaker Basics. Circuit breaker switching is simple to understand. The complexity arises from the diverse variety of available operating mechanisms and their associated controls which direct the circuit breaker switching. Circuit breaker maintenance requires close checking of the circuit breaker manufacturer’s instructions along with understanding the operating and protective controls for the overall electrical system.

a. Actions. Circuit breakers are switching devices that can make (close), carry, and break (open) an electrical circuit under both normal and abnormal conditions. Circuit breakers consist essentially of make-and-break conducting contacts, an arc extinguishing system, an operating mechanism, and an abnormal-conditions current-detection system.

(1) Normal conditions. Normal conditions are manual and automatic actions occurring within the circuit breaker’s ratings and when operational conditions require circuit switching.

(2) Abnormal Conditions. Abnormal conditions are those where excessive or fault current conditions require automatic opening and possibly automatic reclosing after an overcurrent opening.

b. Ratings. Circuit breaker normal ratings are based on ANSI C37.06 (AC High Voltage Circuit Breakers Rated on a Symmetrical Current Basis - Preferred Ratings and Related Required Capability). Maximum ratings are given in Table 4-1. Other continuous current ratings not shown are 1200 and 2000 amperes. Check circuit breaker nameplates for rated short-circuit current.


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33

Table 4-1. Circuit breaker normal ratings Maximum voltage kV rms Maximum continuous current,

amperes Interrupting time cycles2

4.76 3,000 5 8.25 2,000 5

15/15.51 3,000 5 25.8 2,000 5 38 3,000 5

48.3 3,000 5 72.5 3,000 5 121 3,000 3

1First number is for indoor oiless circuit breakers. Second number is for outdoor circuit breakers. 2Oil circuit breakers manufactured before 1975 may have an 8 cycle rating. This rating affects coordination and short

circuit studies; it does not affect maintenance requirements.

4-2. Circuit Breaker Conducting Contacts and Arc Extinguishing Processes. Circuit opening of the conducting contacts causes an arc to form which is extinguished by various methods. Examples of the various types of arc extinguishing media are shown on Pictures 4-1, 4-2, 4-3, and 4-4.


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34

Picture 4-1 Air-magnetic circuit breaker

Picture 4-2 Oil-insulated circuit breaker


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35

Picture 4-3 Vacuum circuit breaker

Picture 4-4 SF6-insulated puffer-type circuit breaker


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36

a. Conducting Contact Opening. An energized circuit breaker draws an arc when its conducting contacts are separated. The temperature of the arc ionizes the insulating medium and sustains the arc. On current zero, arcing ceases and the voltage across the contacts increases. The voltage buildup results in an arcing restrike from the electric field and from thermal effects of the initial arc’s charged particles Only when the arc is cooled well below its ionization temperature at current zero will the arc be fully extinguished and current interruption accomplished.

b. Extinguishing Methods. Various methods provide arc extinguishing. All methods involve either cooling the arc or providing an insulating atmosphere unfavorable to ionization or to reionization. Arc chutes in air magnetic circuit breakers with their barriers use side-by-side fins through which the arc is drawn by the establishment of a magnetic field. This longer arc is then cooled by convection. Air magnetic circuit breakers have both main and arcing contacts. (See Paragraph 7-2.a.) Oil in oil-insulated circuit breakers vaporizes and forms air bubbles whose hydrogen is unfavorable to ion production. Sulfur hexafluoride (SF6) in SF6-insulated circuit breakers is about 100 times more effective than air in extinguishing the arc. Vacuum in vacuum circuit breakers is an even better arc extinguisher since its high dielectric does not allow ionization to maintain itself and restrike after a current zero.

4-3. Circuit Breaker Operating Mechanisms. An operating mechanism needs some form of energy to open and close the circuit breaker contacts at the required speed. The circuit breaker mechanism must cause acceleration, movement, and deceleration at each opening and closing stroke. Equally important the circuit breaker must stay open or closed until directed either manually or automatically to perform otherwise.


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37

a. Operating Energy. All operating mechanisms use some form of stored energy for opening and closing the circuit breaker. Pictures 4-5, 4-6, 4-7, and 4-8 show examples of various operating mechanisms.

(1) Stored Energy Methods. Table 4-2 indicates some of the various methods of stored energy used to open and close circuit breakers. The method used to close the circuit breaker may not be the same method used to open the circuit breaker. It takes more energy to close a circuit breaker than to open the unit. In both cases the contact motion is slowed by dampers at the end of the stroke.

Table 4-2. Circuit breaker stored energy methods Electrical energy inputs to electrical operators System Voltage to operate

1. Batteries dc 2. Control power transformer (CPT) ac 3. CPT charging a capacitor supplying a

half-wave rectifier dc

Electrical operators 1. Motor wound charged springs 2. Solenoids

Compressed gas methods 1. Hydraulic systems 2. Pneumatic systems


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38

Picture 4-5 Motor/spring operating mechanism

Picture 4-6 Blocking a closing spring before

maintenance work


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39

Picture 4-7 Pneumatic operating mechanism

Picture 4-8 Hydraulic operating mechanism


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40

b. Spring-Operating Mechanisms. The stored energy is usually provided by spring-operating mechanisms. Motor-wound springs store closing/opening energy. Springs are latched either in the closed or the open position until a manual or automatic direction releases them.

(1) Closing. A latch must hold against a large force to prevent the spring from unwinding. By providing a main latch, an in-between latch, and a trip latch in series the necessary releasing electromechanical devices becomes a low-energy system. The three latches act as a mechanical amplifier. A small amount of corrosion, lack of lubrication, proper alignment on the low-energy end of the amplifier can prevent the trip latch from operating. A much greater amount of these defects are needed to prevent the main latch from operating.

(2) Opening. On energizing the trip coil a latch is released or a pilot valve is actuated and the opening operation goes to completion without necessarily requiring the tripping coil to be energized through the entire operation.

c. Pneumatic/Hydraulic Operating Mechanisms. Pneumatic/hydraulic amplifiers have a main valve operated by a pilot valve (directed by the closing or tripping coil). Their design lowers the electromechanical energy requirement.

d. Auxiliary Devices. Auxiliary contacts indicate the circuit breaker position by energizing indicating lights. Auxiliary contacts signal the need for early replacement of stored energy spring winding motors, hydraulic pump/air compressors, and other auxiliary devices when contacts are provided that monitor the adequacy of that stored energy device.


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41

e. Interlocks. Interlocks prevent releasing the closing spring when the circuit breaker is already closed or operating the unit as it is moved from the connected position to the test or to the disconnected position.

f. Safety. Isolate control and current, and voltage instrument transformer secondary circuits to protect against unintentional operation.

(1) Control Circuits. Understand the control method including interconnecting circuits and remove control fuses, open test switches, and disable any other control inputs. Lockout/tagout precautions should cover all isolating requirements.

(2) Closing/Opening. Circuit breakers are both opened and closed with stored energy mechanisms which may remain charged even when a circuit breaker has been withdrawn from its enclosure. The mechanisms may be still capable of operating the circuit breaker in the withdrawn position. If the circuit breaker is closed, make sure the opening device circuit is discharged before you approach it with your tools or fingers. If the circuit breaker is open, block it and wire the trip latch to prevent the circuit breaker from closing. Above all, read the manufacturer’s instructions so that you can predict the condition of the circuit breaker.

4-4. Circuit Breaker Elementary Diagrams. Review the circuit breaker elementary diagram provided in the manufacturer’s instructions. Check any modifications given in the operations manual for the specific system. The effect of open-close-trip actuators, control operating power input, open and close activating and monitoring devices, and safety interlocks all impact on the circuit breaker operating mode. That impact can affect the safety of the maintenance technician and the continued operation of the device. An elementary diagram of a spring-operated circuit breaker mechanism is shown on Figure 4-1 and the mode of operation discussed in Figure 4-2.


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42

V

N

OPERATIONLS1 OPEN UNTIL SPRINGSaa ARE FULLY CHARGEDLS1 CLOSED UNTIL SPRINGSbb ARE FULLY CHARGEDLS2 OPEN UNTIL SPRINGSaa ARE FULLY CHARGEDLS2 CLOSED UNTIL SPRINGSbb ARE FULLY CHARGEDLC OPEN UNTIL MECHANISM IS

RESETPS1 OPEN IN ALL EXCEPT

BETWEEN “TEST” AND“CONNECTED” POSITIONS

PS2 CLOSED IN ALL EXCEPTBETWEEN “TEST” AND“CONNECTED” POSITIONS

ABBREVIATIONSCS - BKR. CONTROL SWITCH - CLOSECCS - BKR. CONTROL SWITCH - TRIPTY - ANTI PUMP RELAYSR - SPRING RELEASE COIL (CLOSE COIL)M - SPRING CHARGING MOTORST - SHUNT TRIP COILPR - PROTECTIVE RELAYV - SECONDARY DISCONNECT52 - CIRCUIT BREAKERa - OPEN WHEN 52 IS OPENb - CLOSED WHEN 52 IS OPEN

9

6

52

73A3

4LS1aa

13

52 b

5

a52

14

52 a

10

192021

6

b

LC

LS2aa

LS2bb

PS1

PS2

LS1bb

24

DC

SOURCE

PRCST

RLGL

ST1

SR

432

M Y

1

CSCWL

P

SPRINGCHARGEDINDICATINGLIGHT

Yb

Ya

Figure 4-1 A typical circuit breaker elementary diagram


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As soon as the secondary disconnects engage, the spring charging motor automatically startscharging the closing springs provided the control power is available. When the springs arecharged, the motor cut off (LS1/bb and LS2/bb) switch turns the motor off. The breaker maybe closed by making the control switch close (CS/C) contact. Automatically upon closing of thebreaker, the motor starts charging the closing springs. The breaker may be tripped any time bymaking the control switch trip (CS/T) contacts.

Note the position switch (PS) contact in spring release (SR) circuit in the scheme. This contactremains made while the breaker is being levered between Test and Connected position.Consequently it prevents the breaker from closing automatically even though control switchclose contact may have been made while the breaker is levered to the Connected position.

When the CS/C contact is made, the SR closes the breaker. If the CS/C contact is maintainedafter the breaker closes, the Y relay is picked-up. The Y/a contact seals in Y until CS/C isopened. The Y/b contact opens the SR circuit so that even though the breaker wouldsubsequently open, it could not be re-closed before the CS/C were released and remade. Thisis the anti-pump function.

Figure 4-2 Operating control modes for Figure 4-1


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4-5. Circuit Breaker Nameplates. Circuit breaker nameplate data can provide useful information when Apparatus Documentation data is not available or has been lost. Tables 4-3 and 4-4 show minimum circuit breaker information required on circuit breaker nameplates for low-voltage circuit breakers and for medium and high voltage circuit breakers respectively.

Table 4-3. Low-voltage circuit breaker minimum nameplate information

Power circuit breakers Manufacturer’s name Type of circuit breaker Rated continuous current of trip devices

(where applicable) and type designation Frame size Rated maximum voltage(s) Rated short-circuit current at each rated maximum

voltage

Rated short-time current (where applicable) Suitable fuse type and sizes (where applicable) Rated frequency Rated control voltage (where applicable) Year of manufacture, by date or code Identification number Manufacturer’s data sheets or instruction book

reference


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Table 4-3. Low-voltage circuit breaker minimum nameplate information (cont.)

Molded-case circuit breakers Manufacturer’s name or trademark Type designation or identification number Rated current Rated operational voltages with

corresponding rated short-circuit breaking current1

Indication of a required barrier2

LINE and LOAD (if it is an interchangeable trip circuit breaker or is not suitable for reverse connection)

Rated short-time withstand current (if applicable) ON and OFF for indicating the closed and open

positions at the place of operation.3

1For circuit breakers rated 250 V maximum with short circuit breaking current of 5000 amperes, the short circuit breaking current shall be permitted to be omitted.

2If the proper operations or installation is a dependent upon an insulation barrier 3If symbols are used, “O” will be used to indicate the open and “I” will indicate the closed position.


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Table 4-4. Medium and high voltage circuit breaker minimum nameplate information

Circuit breaker Manufacturer’s name Manufacturer’s type designation Manufacturers serial number Year of manufacture Rated frequency Rated continuous current Rated maximum voltage (kV) Rated voltage range factor K Rated full wave impulse withstand voltage (kV) Rated switching-impulse withstand voltage

! Terminal to ground - circuit breaker closed ! Terminal to terminal - circuit breaker open

Rated line closing switching surge factor Rated short-circuit current Rated interrupting time Normal operating pressure Minimum operating pressure Gallons of oil per tank or weight of gas per breaker Weight of circuit breaker complete (with oil or gas) Instruction book number Parts list number Assigned out-of-phase switching current rating


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Table 4-4. Medium and high voltage circuit breaker minimum nameplate information (cont.)

Ratings for capacitance current switching Transient overvoltage factor Open-wire line charging current Isolated shunt capacitor bank current

Back-to-back shunt capacitor bank current Transient inrush current peak Transient inrush current frequency

Operating mechanism Manufacturer’s name Manufacturer’s type designation Manufacturer’s serial number Year of manufacture Closing control voltage range Tripping control voltage range Closing current Tripping current

Compressor control switch closing and opening pressures

Low pressure alarm switch closing and opening pressures

Low pressure lockout switch closing and opening pressures

Wiring diagram number Instruction book number Parts list number


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Table 4-4. Medium and high voltage circuit breaker minimum nameplate information (cont.)

Current transformers1 Manufacturer’s name Manufacturer’s type designation Rated frequency, if other than 60 cycles American National Standard accuracy class Instruction book number Curve sheet

Connection chart showing: ! Full winding developing ! Taps ! Ratio in terms of primary and secondary

currents ! Polarity ! Pole and pocket location

Accessories Identification Pertinent operating characteristics

1Nameplates located at respective terminal blocks. Includes mutual reactance and self-impedance (resistance, reactance, and impedance) for linear couplers.


AFH 32-1282V1

Chapter 5. Circuit Breaker Testing AFH 32-1282V1

49

CHAPTER 5. CIRCUIT BREAKER TESTING 5-1. De-Energized Circuit Breaker General Tests. Always test circuit breakers in the test position. If there is no test position (stationary circuit breakers) test only after the circuit breaker has been de-energized and grounded. Tests must be done in accordance with the safety requirements for de-energized electrical line work given in Paragraph 1-4. Convert measured insulation resistances and power factors from the test temperature to the reference temperature of 20 degrees C (AFMAN 32-1280(I)).

a. Contact Resistance Tests. Repeated arcing or excessive corrosion of circuit breaker contacts increases contact resistance which is detrimental to the contact’s ability to carry current. Increased contact resistance may also indicate loose joints or misaligned contacts.

(1) Application. Apply a direct-current source (of at least 100 amperes of current for medium and high voltage circuit breakers) from the circuit breaker’s input terminal/bushing to its output terminal/bushing. Close the circuit breaker and with a low-resistance instrument measure the resistance of each pole. The average resistance values for 15-kV-class circuit breakers should normally be between 200 and 250 micro-ohms.

(2) Test Values. The resistance should not exceed the values specified by the circuit breaker manufacturer for the type, voltage, and current rating of the circuit breaker. Contact resistance varies with low-voltage circuit breakers and usually is measured by millivolt drop rather than micro-ohm resistance. In the absence of manufacturer’s data compare the measured pole’s contact resistance to adjacent poles and/or to similar circuit breakers ratings. Investigate any deviations exceeding the


AFH 32-1282V1


50

manufacturer’s tolerance or any deviation of more than 50 percent if compared to similar circuit breakers or adjacent poles.

b. Insulation Resistance Pole-to-Pole Tests. This test is meaningful only on a comparative basis. A gradual decline in resistance with age is normal; however, a sudden decline means insulation failure is imminent. A continued downward trend indicates insulation deterioration, even through measured resistance values are above the minimum acceptable limits.

(1) Application. Use a megohmeter to measure insulation resistance with the circuit breaker in both the open and closed positions.

(a) Circuit Breaker Open. Connect the megohmeter lead to one input or output pole terminal of the circuit breaker with all other five pole terminals grounded. Repeat for the other five terminals.

(b) Circuit Breaker Closed. Connect the megohmeter lead to one closed pole (either input or output) terminal of the circuit breaker with either the input or output of the other two closed pole terminals grounded. Repeat for the other two phases.

(c) Test Values. Take the ambient temperature during measurements. Correct the measured insulation resistance and record. Compare with acceptance and previous test values. See Table 5-1 for test voltages and minimum insulation resistances.

Table 5-1. Circuit breaker insulation-resistance test values Voltage rating Minimum dc test voltage Recommended minimum insulation

resistance in megohms 0-250 volts 500 volts 50

251-600 volts 1000 volts 100 601-5000 volts 2500 volts 1000


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5001-15000 volts 2500 volts 5000 15001-25000 volts 5000 volts 20000

35,000 - 69,000 volts 15,000 volts 100000 c. Control Wiring Insulation-Resistance Tests. Perform insulation-resistance tests at

1000 volts direct current. Do not perform the test on wiring connected to solid-state components. Insulation resistance should be a minimum of 2 megohms.

d. Insulation Power Factor Tests. Use an insulation power factor test set in accordance with the test set’s instructions. The use of the set requires previous training and the set manufacturer should supply test-data forms. Limit test voltages to below the line-to-line voltage rating of the circuit breaker. Take measurements which allow computation of the power factor based on the measured insulation watts loss divided by the volt-amperes applied. Check power factor for both open and closed positions of the circuit breaker. Power factor test results should be evaluated on the basis of previous results but any value above 1 percent warrants investigation.

(1) Precautions. Power factor measurement instrumentation must be well shielded if it is used in a substation area where there may be a significant level of electrostatic interference. Using a higher frequency power supply may help solve the interference problem.

(2) Advantages: The insulation power factor test can detect defective insulation in series with good insulation, a condition that may be masked when using the insulation resistance test. The insulation resistance test may indicate a false low value of resistance because of the many parallel paths and the variation due to the volume of the insulation system. A negative power factor is an indication of tracking across the insulation system.


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e. Dynamic Travel Tests. Use a motion analyzer to check mechanical operation of the circuit breaker at full speed. Compare circuit breaker travel and velocity values to the manufacturer’s acceptable limits and with the historical record for the circuit breaker. Small variations in speed or travel can indicate deteriorating conditions of the circuit breaker’s closing mechanism, stored energy system, shock absorbers, and other mechanical parts.

f. Trip and Close Coil Minimum Operating Voltage Tests. For circuit breakers without integral diagnostic capabilities, connect a switch and rheostat in series with the coil circuit (trip or close) being checked and across the terminals to the applicable remote control switch. Connect a voltmeter across the coil. Starting at below 50 percent of rated coil voltage, gradually increase the voltage until the coil plunger picks up and successfully operates the circuit breaker. Make several trial operations of the circuit breaker, and record the minimum operating voltage.

(1) Tripping. Most circuit breakers should trip at about 55 percent of rated trip-coil voltage. Measure the trip-coil resistance and compare it with the factory test value to disclose shorted turns. Many modern circuit breakers have trip coils which will overheat or burn out if left energized for more than a short period. An auxiliary switch is used, in series with the coil, to open the circuit as soon as the circuit breaker has opened. The auxiliary switch must be properly adjusted to successfully break the arc without damage to the contacts.

(2) Closing. Follow the same procedure for determining the minimum closing coil voltage. Record the minimum voltage that will close the breaker and the closing coil resistance.


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5-2. De-Energized Tests Specific to the Circuit Breaker Type. The voltage rating and the type of insulation requires tests specific to the circuit breaker design.

a. Low-Voltage Circuit Breakers. The protective tripping device is an integral part of the circuit breaker. The unit may be equipped with an electromechanical trip unit or a static trip unit. Electromechanical units may have a thermal (inverse time overload) protection, magnetic (instantaneous short-circuit) protection, or a thermal-magnetic combination. Static units are solid-state electronic devices which provide many additional protective features. All tripping times should be checked to assure they meet the manufacturer’s time-current characteristic tolerance band. Use a circuit breaker test set and make field adjustments in accordance with the test set’s instruction. Do not compromise the protection by exceeding the trip unit’s adjustable range. Field repair is not recommended. If the trip unit is not functioning properly it should be replaced. It may also be advisable to replace the entire circuit breaker.

b. Oil-Insulated Circuit Breakers. Check oil dielectric strength, power factor, interfacial tension, and color in accordance with requirements given for insulating liquid tests in AFH 32-1282V2.

c. SF6-Insulated Circuit Breakers. Check for moisture content. Service-aged moisture content should be less than 300 parts per million (ppm) by volume (10 ppm new). Do not energize any gas-insulated equipment where the gas density is less than 50 percent of nominal or if the moisture content exceeds 1,000 ppm. Moisture content should be checked with a moisture analyzer approved for SF6 gas. Follow the procedures in and as often as recommended by the manufacturer’s instructions. Some SF6 bottles have a sample valve. Some SF6 bottles are sampled through a filling valve using a valved sampling tube arrangement which prevents contaminants from entering the SF6 bottle. It is recommended that trained contract personnel do the checking.


AFH 32-1282V1

Chapter 6. Circuit Breaker Evaluations AFH 32-1282V1

53

CHAPTER 6. CIRCUIT BREAKER EVALUATIONS 6-1. Circuit Breaker EPM Reports. Each installation should prepare local blank EPM report forms to be filled out by the inspecting technicians. (See Paragraph 1-4.) The following tables indicate data which may need to be recorded. Evaluate the extent of data required based on your installation needs and maintenance ability.

a. Basic Circuit Breaker Information To Be Determined Before The Inspection. Provide a suitable record header with blank spaces for insertion of the following data given in Table 6-1.

Table 6-1. Circuit breaker general data Designation

Date of inspection Location Serial no.

Year installed Last inspection date

Manufacturer Instruction manual

Insulation (air, vacuum, SF6, oil)

Voltage rating Rated continuous amperes Rated interrupting amperes

Operation (manual, electrical, remote control) Volts close: ac_____ dc______ Volts trip: ac_____ dc______

Assembly (switchboard, switchgear, none) Type (stationary, drawout)

Protective device type and settings b. Basic Inspection Items To Be Checked. Provide an inspection listing with column

headings covering items to be checked off for each listed number as given in Table 3-4.


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c. Inspection Items To Be Covered. Inspection items to be covered will vary dependant upon the voltage level and insulation type of the circuit breaker as covered in the following paragraphs of this chapter. Table 6-2 indicates circuit breaker readings and appropriate evaluation paragraphs for passing criteria applying to the various circuit breaker types. See AFH 32-1282V2 for bushing, instrument transformer, and surge arrester requirements.

Table 6-2. Circuit breaker readings or test values Readings or test value Evaluation reference paragraph 1. Ambient temperature .......................................................................... -- 2. Number of operations ......................................................................... -- 3. Peak indicating amperes .................................................................... -- 4. Contact resistance pole-to-pole (microhms)....................................... 5.1a 5. Insulation resistance (megohms) open, closed1................................. 5.1b 6. Control wiring insulation resistance (megohms) ................................ 5.1c 7. Power factor ....................................................................................... 5.1d 8. Closing speed..................................................................................... 5.1e 9. Opening speed ................................................................................... 5.1e 10. Trip and close minimum operating voltage......................................... 5.1f 11. Low-voltage circuit breaker tripping times.......................................... 5.2a 12. SF6 moisture content ......................................................................... 5.2c 1For six open terminals, and for three closed phases.

6-2. High-Voltage SF6 or Oil Insulated Circuit Breakers. Inspection includes both external and internal inspections. External inspections are covered in Table 6-3. Follow procedures of Table 6-4 for internal tank inspections.


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Table 6-3. External high-voltage circuit breaker checks Component Inspection Component Inspection

1. Tanks a. Paint condition b. Bulging, cracking, leaks c. Gasketing or other sealing adequacy d. Valves open or closed e. Pressure, air or gas f. Support adequacy

2. Operating mechanisms1 a. General condition b. Control cabinet condition c. Mechanical clearances d. Pneumatic operating systems e. Hydraulic operating systems

3. Electrical connections a. Tightness b. Hot spots2

4. Protective device operation/calibration a. Control circuits b. Relays c. Alarms d. Gauges e. Relief devices f. Calibrations

5. Oil insulation a. Filling b. Filtering c. Sampling

6. SF6 insulation3 7. Operation under load

a. Malfunctions b. Friction

8. Heater operation 1May require lubrication, cleaning, adjusting, and aligning. 2For infrared checking see Paragraph 3.1.a. 3See Table 6-2.


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Table 6-4. Internal high-voltage circuit breaker tank procedures and checks 1. Accessing the tank

a. Remove covers, lower tank, extract oil or gas and transfer to approved storage or processing equipment

b. Ventilate and wipe down oil-insulated units. Pull a vacuum on gas insulated units.

c. Check, measure, adjust, lubricate, align, and repair:

(1) Contacts (2) Interrupters (3) Internal current transformers (4) Resistors, capacitors, and lift rods

d. Replace any desiccant material, if applicable

2. Seal the tank and: a. Refill oil-insulated units to the proper

level and inspect for leaks b. Pull a vacuum per manufacturer’s

specified time for gas-insulated units and if no leaks are present refill tank to the proper pressure

6-3. Medium-Voltage Vacuum or Air Insulated Metal-Clad Switchgear Circuit Breakers. Pictures 6-1 and 6-2 indicate protective features on all metal-clad switchgear. Pictures 6-3 and 6-4 indicate details of air-magnetic arc chutes. Table 6-5 indicates circuit breaker components and appropriate inspection actions for circuit breakers withdrawn from the switchgear and de-energized unless indicated to be in the test position. BE CAUTIONED THAT HIGH POTENTIAL TESTING OF VACUUM BOTTLES CAN CAUSE X-RAY EMISSION. USE MANUFACTURER’S SAFETY PRECAUTIONS.


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Picture 6-1 Closed protective shutters

Picture 6-2 Open protective shutters


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Picture 6-3 Exposing arc chutes

Picture 6-4 Cleaning an arc chute


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Table 6-5. Medium-voltage metal-clad switchgear circuit breaker checks Component inspection 1. Anchorage and grounding 2. Operating mechanism check

a. Electrical operations functions1, tripping, closing, trip-free, antipump, and protective relaying

b. Mechanical operations, tripping, closing, charging, and contact alignment in all positions

c. Tightness of hardware d. Cleanliness e. Lubrication requirements f. Racking mechanism, cell fit, and element

alignment g. Inspect wiring for security, damage, and

terminal connections

Component inspection 3. Air magnetic unit inspections2

a. Main contacts wipe and gap3 b. Arcing contacts wipe3 c. Finger clusters d. Secondary disconnect contacts e. Latches wipe and clearance3 f. Contact travel4 g. Clearances3 h. Speed, opening and closing3 i. Moving parts, linkages, closing/tripping

mechanisms, freedom of movement position for quick actions

j. Interlocks properly operating k. Arc chutes

4. Vacuum unit inspections a. Contact erosion and wipe5 b. Adequate vacuum

1With circuit breaker in the test position and using a test coupler. 2Remove arc chutes for inspection 3Record manufacturer’s recommendation, as found condition, and as left condition. 4Measure overtravel and determine from manufacturer’s instructions if any measured overtravel is acceptable. 5Provide a one-minute alternating-current high potential in accordance with the manufacturer’s instructions. See previous

caution.


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6-4. Low-Voltage Circuit Breakers. Table 6-6 indicates circuit breaker components and appropriate inspection actions. Drawout circuit breakers should be removed from their enclosures. Stationary circuit breakers should be de-energized and grounded. Pictures 6-5 and 6-6 show the two usual type of low-voltage circuit breakers. Pictures 6-6 and 6-7 show drawout contacts for power and control respectively.

Table 6-6. Low-voltage circuit breaker checks Component inspection 1. General

a. Mounted properly and grounded b. Undamaged and clean c. Operates correctly d. Tight connections e. Arc chutes and contacts1

Component inspection 2. Drawout units

a. Racking mechanism, cell fit and element alignment. Verify contact wipes and other adjustments are correct.

b. Operating mechanism functions both electrically and mechanically

c. Lubrication requirements d. Control devices

1On nonsealed units.


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Picture 6-5 Molded case circuit breaker

Picture 6-6 Power circuit breaker


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Picture 6-7 Power contact fingers

Picture 6-8 Control contact fingers


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Chapter 7. Interrupter Switch Installations AFH 32-1282V1

63

CHAPTER 7. INTERRUPTER SWITCH INSTALLATIONS 7-1. Interrupter Switch Basics. Interrupter switches provide an economical alternative to the use of medium-voltage circuit breakers.

a. Actions. Interrupter switches can make (close), carry, and break (open) electrical circuits. They operate as well as circuit breakers under normal conditions. Under abnormal conditions their fault-interrupting capabilities (fused interrupter switches) do not approach that of a similarly rated circuit breaker. Closing in on faults can be dangerous if the switch does not have a duty-cycle fault-closing rating (fault-initiating switch). Motor operators for remote opening/closing of switches are available. Their use has diminished in recent years because of their many operating problems.

b. Ratings and Nameplates. Standard switch and fuse ratings from manufacturers are given in Tables 7-1 and 7-2 respectively. Verify ratings with the applicable switch nameplate. Tables 7-3 and 7-4 show minimum switch and fuse nameplate information required by industry standards.


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Table 7-1. Interrupter switch ratings. Rated

maximum kV Impulse

withstand kV Continuous and

load-break amperes

Fault-close and momentary

amperes kA rms asym.

Rated short-time current (2 seconds) kA rms sym.

5 60 600 40 25 5 60 600 61 38 5 60 1200 61 38

15 95 600 40 25 15 95 1200 40 25 15 95 600 61 38 15 95 1200 61 38 27 125 600 40 25 27 125 600 60 38 38 150 600 30 25


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Table 7-2. Fuse ratings Continuous Interrupting rating at kV Current Range 4.8 kV 15 kV 25.8 kV 27 kV 38 kV Amperes kA symmetrical

Boric acid type 10-200 19 14.4 10.5 6.9 6.9 .5-400 37.5 29.4 --- --- --- .5-400 --- 34.8 --- --- --- .5-720 37.5 29.4 --- --- --- .5-300 --- --- 21 16.8 16.8 .5-540 --- --- 21 16.8 16.8

Current-limiting type 20-450 50 --- --- --- --- 20-250 --- 50 --- --- --- 7-100 --- --- --- 35 --- 10-80 --- --- --- --- 12.5


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Table 7-3. Interrupter switch minimum nameplate information Interrupter switches

Manufacturer’s name and address Manufacturer’s type and designation numberRated maximum voltage Rated continuous current1 Short-time current ratings1 ! Rated momentary current ! Rated three-second current Rated impulse withstand voltage [basic

impulse insulation level (BIL)] Rated frequency Allowable continuous-current class1

Rated interrupting current and the following, where applicable:

! Operating life expectancy ! Rated switching current - single

capacitance ! Rated switching current - parallel-

connected capacitance ! Rated differential capacitance voltage

(maximum) ! Rated differential capacitance voltage

(minimum) ! Rated capacitance switching transient

overvoltage ratio Fault-initiating switches

All the above information except as noted Rated making current

Rated closing time Operating life expectancy

1Not required for fault-initiating switches.


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Table 7-4. Fuse minimum nameplate information Manufacturer’s name or trademark or monogram

Manufacturer’s type or identification number Rated continuous current1 Rated maximum voltage

Rated maximum interrupting current 1Type identification C, E, or R where applicable for fuse interchangeability

identification.

7-2. Interrupter Switch Operating Features. Operation may be electrically or mechanically initiated. Safety interlocks may prevent operation. Optional monitoring devices are available. Interrupter switches, like circuit breakers, have a contact and arc extinguishing system, an operating mechanism, and an abnormal-conditions current-detection system. Air is the usual insulating medium and switches are designed only for use on medium-voltage systems.

a. Contact and Arc Extinguishing Process. Generally switches are constructed with both main and arcing contacts. The main contacts carry the continuous current and the arcing contacts break the arcing current. Arc chutes are coated to generate a de-ionizing gas under the heat of the arc. The design lengthens and thus cools the arc promoting rapid extinguishing.


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b. Operating Mechanism. Stored energy from a heavy-duty spring provides the force necessary to open or close the switch. The switch handle charges the spring when operated either up for closing or down for opening. The stored energy of the spring operates independently of the operator. Switches cannot be teased into any intermediate position. All mechanisms can be manually operated. Many interrupter switches are provided with motor operators controlled by the current-detection system. Motor operators have a well documented history of operating problems.

c. Current Detection Systems. The drawback to interrupter switches as compared to circuit breakers is their current-detection system under abnormal operating conditions.

(1) Overloads. On overloads fuses will operate to open the circuit. (2) Fault Conditions. Fuses will operate properly on line-to-line faults. They may not

operate on line-to-ground faults. Therefore safety precautions must be observed when manually opening switches.

d. Precaution in Opening or Closing Switches. These operations can be extremely dangerous if they are performed when there is an uncleared fault condition at the switch. Safety orders should be very clear that the operator must stand to the side of the switch and wear a blast suit and fire-resistant clothing.

e. Safety Interlocks. Interlocks are required by industry standards to prevent contact with energized switch components. Pictures 7-1, 7-2, 7-3, and 7-4 show features that ensure energized parts are isolated from operating personnel.


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Picture 7-1 Interrupter

switch door open

Picture 7-2Operating

mechanism


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Picture 7-3 Interrupter switch fuses exposed

Picture 7-4 Interrupter operating

mechanism exposed


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(1) Standard Switch Interlock Safeguards. Fuses are not accessible unless the switch is open. The switch cannot close when the fuses are accessible. Access to the switch compartment is prevented unless the stored energy mechanism is discharged or blocked.

(2) Drawout Switch Interlock Additional Safeguards. Movement of the removable element is prevented when the switch is in the closed position. The switch cannot be closed (mechanically or electrically) when the removable element is at any intermediate point between the disconnected and connected positions. Movement of the removable element to and from the connected position is prevented if the operating spring is in the charged position.

f. Optional Monitoring Devices. Fuses are often provided with blown fuse indicators. Surge arresters, instrument transformers, meters, relays, and additional interlocks may be installed to protect and monitor the interrupter switch.

7-3. Interrupter Switch De-Energized Device Tests. Perform contact-resistance tests across each switch blade and fuse holder and insulation resistance tests on each pole phase-to-phase and phase-to-ground for one minute with a test voltage in accordance with Table 5-1. See Table 7-5 for test requirements. Always test interrupter switches in the test position. If there is no test position (stationary interrupter switches) test after the interrupter switches have been de-energized and grounded. Tests must be done in accordance with the safety requirements for de-energized electrical line work given in Paragraph 1-4. Convert measured insulation resistances from the test temperature to the reference temperature of 20 degrees C (see AFMAN 32-1280(I)).


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Table 7-5. Interrupter switch test requirements Type Test reference Acceptable test value

1. Ambient temperature -- -- 2. Contact resistance pole-to-pole (microhms) 5.1a 1001 3. Insulation resistance (megohms) 5.1b Table 5-1 1Investigate any values which deviate from adjacent poles or similar switches by more than 50 percent.

7-4. Interrupter Switch EPM Reports. Each installation should prepare local blank EPM report forms to be filled out by the inspecting technicians. (See Paragraph 1-4.) The following tables indicate data which may need to be recorded. Evaluate the extent of data required based on your installation needs and maintenance ability.

a. Basic Interrupter Switch Information To Be Determined Before the Inspection. Provide a suitable record header with blank spaces for insertion of the following data given in Table 7-6.

Table 7-6. Interrupter switch general data Designation Date of inspection Location Serial no. Year installed

Last inspection date Manufacturer Instruction manual Voltage rating Continuous current

Short time currents ! Momentary ! Three-second Operation (manual, electrical) Type (stationary, drawout)


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b. Basic Inspection Items To Be Checked. Provide an inspection listing with column headings covering items to be checked off for each listed number given in Table 3-4.

c. Inspection Items To Be Covered. List inspection items to be covered. Table 7-5 indicates interrupter switch readings and appropriate evaluation paragraph for passing criteria. Table 7-7 indicates interrupter switch components and appropriate inspection actions.

Table 7-7. Interrupter switch checks Component inspection 1. Operating mechanism check

a. Mechanical operations b. Motor operations c. Tightness of hardware d. Cleanliness e. Lubrication requirements f. Racking mechanism, cell fit, and

element alignment g. Inspect wiring for security, damage, and

terminal connections 2. Fuses and holders

a. Failure b. Cleanliness c. Contact surfaces d. Dropout or expulsion feature e. Fuse security

Component inspection 3. Interrupter

a. Main and arcing contacts b. Finger clusters c. Contact travel d. Switch clearances e. Moving parts, linkages, closing/tripping

mechanisms, freedom of movement position for quick actions

f. Interlocks properly operating g. Arc chutes

4. Anchorage and grounding


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Chapter 8. Switchgear and Switchboard Assemblies AFH 32-1282V1

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CHAPTER 8. SWITCHGEAR AND SWITCHBOARD ASSEMBLIES 8-1. Assembly Performance. These assemblies (indoor or outdoor) provide metal enclosures; supporting structures; electrical interconnections and switching; and interrupting, control, metering, and protective devices. Industry standards provide technical and physical distinctions between the various classes of medium and low voltage switchgear and those units defined as low-voltage switchboard. For your safety be aware of these differences when providing maintenance. Pictures 8-1, 8-2, 8-3, and 8-4 show examples of metal-clad medium-voltage switchgear. Pictures 8-5, 8-6, 8-7, and 8-8 show examples of metal-enclosed low-voltage switchgear.

a. Function. In all cases the purpose of the assembly is to provide a degree of protection to the enclosed conductors and equipment and also a degree of protection to personnel against incidentally contacting live parts. Switchboards may not provide individual metal compartments. Switchboard drawout units are not required to provide the automatic shutters and mechanical interlocks required for drawout switchgear. Switchgear is designed to meet IEEE standards. Switchboards are designed to meet NEMA and UL standards.

b. Treatment. Assemblies are enclosed on all sides and the top with sheet metal. They are normally constructed in modules or cubicles which contain one or more (some switchboards) interrupting devices or auxiliary equipment. Access is provided by doors or removable covers. Remember that even for insulated bus THE INSULATION IS NOT DESIGNED TO PROTECT AGAINST ELECTRICAL SHOCK. Check the general features of assembly construction to assure that enclosures, supporting structures, protective barriers, and buses provide the overall equipment and personnel protection which is their principle function.


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Picture 8-1 Medium-voltage switchgear

Picture 8-2 Rolling out a circuit breaker


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Picture 8-3 Circuit breaker operating mechanism

Picture 8-4 Open contacts


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Picture 8-5 Low-voltage switchgear

Picture 8-6 Rear of switchgear


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Picture 8-7 Racking out a circuit breaker

Picture 8-8 Removing control fuses


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c. Construction Requirements. Assemblies are built to specific minimum industry standards as covered by Table 8-1. Major medium-voltage switchgear differences are given in Table 8-2.

Table 8-1. Industry classification for assemblies Classification Voltage level Device requirement Bus

requirement Standard Title

IEEE C37.20.2

Metal-clad switchgear1 Medium, Type MC

Drawout circuit breakers

Insulated

IEEE C37.20.3

Metal-enclosed interrupter switchgear

Medium, Type MEI

Stationary or drawout switches

Bare2

IEEE C37.20.1

Metal-enclosed low-voltage power circuit breaker switchgear

Low Stationary or drawout circuit breakers

Bare2

NEMA PB-2 and UL 891

Deadfront distribution switchboards

Low Stationary or drawout switching devices

Bare2

1Metal-clad switchgear is also classified as metal-enclosed. 2Insulated bus in some cases may be available as an optional manufacturer’s provision, but bare bus is the minimum

requirement.


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Table 8-2. MC/MEI switchgear major differences

Item MC MEI Switching device Drawout circuit breaker Fixed or drawout interrupter switch Compartments Barriered Open Operation Electrical Manual or optional electrical Protection Resettable relays Replaceable fuses Load current switching permitted 1,000 30 Mechanical operations permitted 10,000 500


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8-2. De-Energized Assembly Tests. Tests are generally limited to ground resistance tests on permanent ground systems, and insulation resistance tests on buses and control wiring. See Table 8-3 for test requirements.

Table 8-3. Assembly test requirements Readings or test value Evaluation reference paragraph 1. Ambient temperature...........................................................................-- 2. Infrared ................................................................................................3-1a1 3. Corona.................................................................................................8-3 4. Ground resistance...............................................................................3-1b1 5. Bus insulation resistance ....................................................................5-1b2 6. Control wiring insulation resistance.....................................................5-1c 1Readings should identify location or be provided in a separate report. 2See Table 5-1 for insulation resistance test values.

8-3. Energized Assembly Tests. Always test assemblies in accordance with the safety requirements for energized electrical line work given in Paragraph 1-4. Convert measured insulation resistances from the test temperature to the reference temperature of 20 degrees C (see AFMAN 32-1280(I)). Use a hand-held corona tester to determine if corona is being produced. If corona is present investigate insulation and insulators for corrosion, tracking, or dirt buildup and replace if necessary. Infrared tests should be done as covered in Paragraph 3-1.


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a. Corona Discharges. Electrically charged bodies exert forces (electrostatic) on one another. If the potential gradient between bodies is high enough, the breakdown level of air (as affected by pressure, temperature, and humidity) can be exceeded. This breakdown can cause an electric discharge which results in the formation of corona. Any formation of corona indicates an insulating deficiency. In switchgear, corona (if it occurs) is usually localized in the tiny air gaps between bus bars and its insulation or, between two contiguous insulating members.

b. Corona Actions. Corona ionizes the surrounding air converting oxygen to ozone (O3) and nitrogen and humidity to nitric acid (HNO3). These two by-products along with ion and electron bombardments of organic materials will damage assemblies. Corona should be checked for using a detector at each assembly EPM review. Do not wait until the distinct smell, the popping, spitting, crackling or frying noise, or communication reception interference indicates corona formation.

8-4. Assembly EPM Reports. Each installation should prepare local blank EPM report forms to be filled out by the inspecting technicians. (See Paragraph 1-4.) The following tables indicate data which may need to be recorded. Evaluate the extent of data required based on your installation needs and maintenance ability.

a. Basic Assembly Information To Be Determined Before the Inspection. Provide a suitable record header with blank spaces for insertion of the following data given in Table 8-4.


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Table 8-4. Assembly general data Designation Date of inspection Location Serial no. Year installed Last inspection date Manufacturer Instruction manual

Voltage rating Bus rating Operation (manual, electrical, both) Switching devices Type (circuit breaker, interrupter switch) Elements (stationary, drawout) Assembly (metal-clad or metal-enclosed

switchgear or switchboard)


c. Inspection Items To Be Covered. List inspection items to be covered. Table 8-3 indicates assembly readings and appropriate evaluation paragraph for passing criteria. Table 8-5 indicates switchgear/switchboard assembly components and appropriate inspection items.


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Table 8-5. Assembly checks Component inspection 1. General

a. Heaters b. Ventilation c. Electrical distress d. Corona e. Tracking f. Thermal damage

2. Enclosure a. Structural Integrity b. Grounding c. Surface condition d. Leaks e. Internal moisture f. Dust

Component inspection 3. Hardware

a. Security b. Lubrication

4. Electrical connection and buses

a. Tightness b. Hot spots c. Contamination d. Insulations

5. Miscellaneous a. Spare equipment b. Handling devices c. Interior lighting


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Chapter 9. Battery Installations AFH 32-1282V1

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CHAPTER 9. BATTERY INSTALLATIONS 9-1. Battery Installation Basics. Storage batteries along with their supporting devices are necessary for the protection of electrical distribution systems. Equipment damage is prevented by electrically actuated protective devices. These devices must still sense problems during an electrical power outage. A battery installation provides the necessary back-up electrical source.

a. Operation. A battery installation contains rechargeable electrochemical type cells. A full-float operating battery charger continuously connected to the battery acts to maintain the cells in a charged condition. Battery systems provide low currents for long periods and high currents for short periods. The battery system’s reserve capacity requirements are based on a duty cycle (usually an 8-hour operating time period) for which all continuous and momentary loads must be supplied by the battery with no recharging available from the battery charger. Cells are mounted on racks to eliminate vibration and connected to minimize voltage drops. Installations must be housed for protection from the elements and to maintain the optimum operating temperature of 77 degrees F (25 degrees C) for which they are designed.

b. Battery Electrochemical and Construction Types. A battery cell is composed of the container, the positive plate (electrode), the separator or retainer, the negative plate (electrode), and the electrolyte. The two electrochemical types use either a lead-acid or nickel-cadmium electrolyte. The cell is constructed as either a vented (flooded) or valve-regulated (sealed) unit. For specific information on a particular type, refer to the manufacturer’s instructions. This chapter is applicable to both electrolyte types, except as noted. Tests for valve-regulated construction types are not covered in this handbook. See AFMAN 32-1186, Valve-Regulated Lead-Acid Batteries for Stationary Applications.


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(1) Electrolytes. Lead acid batteries have an acidic electrolyte solution of sulfuric acid (H2SO4) and their nominal voltage is 2.0 volts per cell. Nickel cadmium batteries use an alkaline electrolyte (potassium hydroxide) and their nominal voltage is 1.2 volts per cell.

(2) Construction. The physical size of a vented battery will generally be larger than a valve regulated battery providing the same energy because of the difference in construction.

(3) Details. Pictures 9-1, 9-2, 9-3, and 9-4 show equipment and maintenance details. (a) Vented Batteries. Vented (flooded) cells are constructed with the liquid

electrolyte completely covering (flooding) the closely spaced plates, so that there is a large volume of free electrolyte. Vented units are characterized by a removable vent cap which allows the electrolyte to be checked and adjusted as needed. Overcharge will produce gases which vent through the cell, requiring regular water replacement. Vent caps must be accessible and are provided with flame arresters. Gassing requires ventilation to avoid explosive possibilities and possible corrosive damage to battery terminals.

(b) Valve-Regulated Batteries. Valve-regulated cells are sealed, with the exception of a valve that opens periodically to relieve excessive internal pressure. Once the pressure is relieved the valve closes and reseals. No cell check of an electrolyte level nor the specific gravity of each cell can be made. These batteries are not maintenance-free as some 10 or more maintenance checks are still necessary. Outgassing of these batteries is low at normal charge rates, but it can occur when there is a battery or battery charger failure. Cells can pose a hazard if enclosed so as to inhibit cooling air, or installed so as to place them in the heat flow of electronics which may occupy the same enclosure.


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Picture 9-1 Battery and charger

Picture 9-2 High and low level electrolyte marks


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Picture 9-3 Cleaning a battery terminal

Picture 9-4 Cleaning a battery cell


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c. Precautions. Safety precautions cannot be ignored, since every station battery installation presents hazards. The importance of using safety equipment, such as rubber gloves, goggles, aprons, and of having an eyewash water bottle present, cannot be overemphasized. The three major hazards are from the electrolyte in the battery, the gases emitted by the battery, and the potential electrical short circuit capability available from the battery’s stored energy.

9-2. Battery Installation Readings and Tests. Readings and tests must be done in accordance with the safety requirements for energized electrical line work given in Paragraph 1-4. Convert indicated readings from the test temperature to the reference temperature of 77 degrees F (25 degrees C) (see AFMAN 32-1280(I)). Also see suggested test accessory list for battery maintenance in AFMAN 32-1280(I).

a. In-Service Energized Readings. The following readings should be taken at not less than the indicated interval as given in Table 9-1. Methods for checking resistances include using low- resistance ohmmeters or measuring the millivolt drop during capacity testing. Resistance values may vary greatly, from less than 10 micro-ohms to 100 micro-ohms. If significant changes in resistances (20 percent above installation value) occur, or manufacturer’s recommended limits are exceeded, workers should take corrective action. Maintenance personnel should refer to manufacturer’s recommendations regarding cleaning and re-torquing connections.


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Table 9-1. Battery installation readings Interval Reading

Monthly

1. Ambient temperature. 2. Float voltage measured at the battery terminals. 3. Charger output current and voltage. 4. Pilot cell data: a. Cell voltage. b. Cell specific gravity and electrolyte temperature, corrected for temperature1. c. Electrolyte level.

Quarterly

1. Ambient temperature. 2. Float voltage measured at the battery terminals. 3. Charger output current and voltage. 4. Measure 10 percent of intercell connection resistances chosen at random. 5. Voltage of each cell. 6. Specific gravity of each cell, corrected for temperature1. 7. Electrolyte temperature and level of one out of each six cells chosen at random.

Annually

1. All of the quarterly readings. 2. All cell-to-cell and cell-to-terminal connection resistances. 3. Infrared readings.

1Does not apply to flooded nickel-cadmium cells.


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(1) Importance of Correct Conductive Path Resistances. The majority of catastrophic battery failures can be traced to problems within the conduction path of the battery system. The conduction path includes all internal buses, terminal posts, and connecting straps between cells.

(2) Connections. All connections must remain tightened to manufacturer’s recommended torque specifications to avoid sparking or excessive heat buildup, possibly resulting in a battery fire. All connections should be checked for proper torque requirements annually and after a heavy discharge. Cell-to-cell and cell-to-terminal resistances should be checked and recorded after torquing.

b. Out-of-Service Energized Tests. The objective of battery testing is to ensure that the battery system can store the required energy and deliver it efficiently when the need arises. A capacity test can evaluate the battery’s ability to store the required energy and deliver constant current over extended periods. An integrity test can determine whether internal battery deterioration or connection path problems (such as corrosion) would prevent efficient delivery of energy. Each of these tests requires that the battery be disconnected from the battery charger and tested using an artificial load. The test disconnection period must have been approved and scheduled so that equipment operation affected by these tests is not jeopardized. This means an approved and specific date and period for the test.

(1) Capacity Load Test. Capacity test duration should be equal to the duty period for which the battery was sized (usually 8-hours). The procedure is given in Table 9-2. Provide at least every 5 years until the battery shows signs of degradation or has reached 85 percent of its life expectancy. Then provide the test every year. Sufficient degradation capacity to warrant annual capacity testing varies among battery types. (See Table 9-3.)


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Table 9-2. Capacity test procedures 1. Pre-test conditions, test criteria, parameters, and “stringency” are decided in advance. 2. Battery is isolated from charger and normal load. 3. Constant artificial load is applied through final test voltage or the test duration. 4. Constant current or power loading depends on the application and published data. 5. The objective is to derive the percent actual capacity by comparing actual time to reach a final

test voltage to specified nominal time.

Table 9-3. Battery capacity degradation1 Battery type Degradation Flooded lead-

calcium A drop of 2 percent per year in capacity from the previous capacity test, or the

capacity is below 90 percent of the manufacturer’s rating. Flooded nickel-

cadmium A drop in capacity in excess of 1.5 percent per year of rated capacity from the

previous capacity test. Valve-regulated The intervals between battery capacity tests are left to the discretion of the

maintenance personnel. Although no drop in battery capacity should occur during the lifetime of the battery, a battery capacity test should be performed at specific intervals as a part of the routine maintenance of the battery system or as abnormal conditions warrant.

1Indicating a need for yearly capacity tests.


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(2) Integrity Load Test. Provide anywhere from quarterly to annually depending on the relative importance of the equipment that the battery supports. The procedure is given in Table 9-4.

Table 9-4. Integrity test procedures 1) The charger/rectifier is disabled, that is removed or the output disconnected. 2) The battery remains connected to normal load and is forced to supply power to the normal load.

Where the normal load is slight, a momentary artificial load should be added. 3) The depth of discharge is very shallow - typically 0.33 to 0.75 amperehour will be consumed. The

critical test parameter is the magnitude of the BATTERY’S momentary load current. It must be great enough to detect abnormal path resistances. Duration of the discharge is just long enough to measure each cell’s voltage under load.

4) Conduction path problems are detected by comparing test data of repeated tests over time, or analyzing cell to average cell data of a specific test.

9-3. Battery Installation EPM Reports. Each installation should prepare local blank EPM report forms to be filled out by the inspecting technicians. (See Paragraph 1-4.) The following tables indicate data which may need to be recorded. Evaluate the extent of data required based on your installation needs and maintenance ability.


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a. Basic Battery Installation Information To Be Determined Before the Inspection. Provide a suitable record header with blank spaces for insertion of the following data given in Table 9-5.

Table 9-5. Battery installation general data Battery

Designation Location

Last inspection date Date of inspection

Year installed Manufacturer

Serial no. Instruction manual

Cell type Cell size

No. of cells Ampere-hours at ______ hour rate

Nominal specific gravity at 77 degrees F1

Nominal system float voltage

Battery charger Designation

Location Last inspection date

Year installed Date of inspection

Manufacturer Serial no.

Instruction manual Nominal system

Float voltage 1Does not apply to flooded nickel-cadmium cells.


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c. Inspection Items To Be Covered. List inspection items to be covered. Tables 9-1, 9-2, 9-3, and 9-4 indicate battery installation readings and tests and appropriate evaluation paragraph for passing criteria. Tables 9-6, 9-7, and 9-8 indicate battery installation components and appropriate inspection actions.

Table 9-6. Lead-acid battery installation corrective actions Electrolyte level Add water to the high water line Cell temperatures Deviation of more than 3 degrees C requires determination of cause1, Resistance Increase of more than 20 percent above installation value, clean, retorque, and

retest connections Float voltage Adjust to be in recommended operating range Specific gravity Provide equalizing charges if individual cell or average for all cells specific gravity

drops more than 10 points2 Cell voltage Provide an equalizing charge immediately if any cell voltage is below 2.13 volts at

the time of inspection 1Replace for short-circuited units. Adjust environment if caused by outside conditions. 2Adjusted for temperature and electrolyte level. Drop is for difference of individual cells from average of cells at time of

inspection or for all cells from the average installation value.


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Table 9-7. Nickel-cadmium battery installation corrective actions Electrolyte level Add water to the high water line Resistance Increase of more than 20 percent above installation value, clean, retorque, and retest

connections Float voltage Adjust to be in recommended operating range Cell voltage Provide a high-rate charge if possible if any cell voltage is found to be 1.35 volts or less.

Table 9-8. Battery installation checks Component inspection 1. Batteries a. Physical damage b. Cleanliness c. Corrosion or leakage d. Tightness of connections e. Cell cracks f. Unintentional ground

g. Verify vent cap and flame arresters in place1 h. Electrolyte appearance 2. Racks a. Cleanliness/corrosion b. Structural integrity

Component inspection 3. Battery Chargers a. Accuracy of meters b. Operation of timers c. Temperature (by touch) d. Fuse failure e. Alarms f. Proper relay settings g. Cleanliness/corrosion h. Connections


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Chapter 10. Protective Sensing, Processing, and Action Devices AFH 32-1282V1

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CHAPTER 10. PROTECTIVE SENSING, PROCESSING, AND ACTION DEVICES

10-1. Device Performance. Electrical systems operate because control devices or systems function:

! to sense and indicate operating parameters within design requirements for user information (instruments and meters)

! to process the data when operating parameters have increased to values in excess of design requirements (protective relays and alarms)

! to actuate protective devices when such action is needed to prevent equipment damage (overcurrent and fault interrupting protective and switching devices).

a. Indicating Devices. Indicating devices include instruments and meters. (1) Electrical Instruments. Industry standards define electrical instruments as devices

used to measure the present value of electrical quantities under observation. An instrument may be an indicating instrument or a recording instrument. By this definition ammeters, voltmeters, and frequency meters are instruments, not meters.


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(2) Electrical Meters. Industry standards define electrical meters as devices used to measure and register the cumulative value of electrical quantities with respect to time. For example, a watthour meter is used to measure and register the amount of average electrical power over a period of time.

(3) Electrical Measurements. Many units measuring ac values will do so using average, peak, or effective values, based on the assumption that the system provides a pure sine wave. With the growing use of solid-state equipment, the waveforms being measured are increasingly less like a pure sine wave. Resulting measurements made from equivalent rms instruments or meters can be misleading, but such results are not necessarily the fault of the measuring device. Whenever possible use true rms instruments or meters.

b. Protective Relays. A relay is an electrical device designed to interpret input data in a prescribed manner. When specific input conditions occur, the relay responds to cause contact operation or a similar sudden change in associated electric control circuits. Protective relays are designed to operate circuit breakers and contactors, usually medium-voltage units. Relays can be set more precisely than fuses. Relays are adjustable with respect to both time and current, a feature that also applies to solid-state, direct-tripping, low-voltage circuit breakers. Input data analyzed is usually electrical, but may be mechanical or thermal, or evaluate other conditions or a combination of conditions. Electrical conditions can be overcurrent, overvoltage or undervoltage, a combination of current and voltage, current balance, direction of current flow, frequency, impedance, or other electrical data.


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c. Alarms. A predefined change in the condition of equipment or the failure of equipment to respond correctly can operate audible or visual indications to announce that the condition needs personnel attention. Alarms can vary from target indications or relays or contact closures operating audible gongs with silencing switches or annunciators with nonautomatically reset devices.

d. Safety Items. Isolate control circuits, that is remove control fuses, open test switches, and operate selector controls as required.

(1) Other Circuits. Keep other overlapping and interconnecting control circuits associated with operating equipment de-energized if necessary for safety.

(2) Secondary Control Circuits. Isolate control, current, and voltage transformer secondary circuits to protect against unintentional operation from tests on the device being checked.

10-2. Device Testing. Always test devices in the test position. If there is no test position operate after the device has been de-energized and grounded. Tests must be done in accordance with the safety requirements for de-energized electrical line work given in Paragraph 1-4. Electrically confirm that current transformer and voltage transformer secondary circuits are intact.

a. Instruments and Motors. Calibration and adjustment are required to meet the requirements of AFMAN 32-1280(I) and to meet the manufacturer’s published data on accuracy.

b. Protective relays. Verify satisfactory performance of each control, protective functions and alarm in accordance with the protection scheme and manufacturer’s instructions. Perform the tests given in Table 10-1.


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Table 10-1. Relay tests Test Criteria

Insulation resistance test on each circuit to frame1 Manufacturer’s instruction manual Pickup parameters on each operating element System protective requirements Timing test on at least two points on the time current curve System protective requirements Pickup target and seal-in unit operation System protective requirements 1Do not perform this test on solid-state relays.

c. Pickup Parameters. Relays are selected to perform certain functions. To standardize on reference use, they are given device function numbers by IEEE C37.2 (Standard Electrical Power system Device Function Numbers). (Device function numbers also describe other electrical power apparatus equipment in addition to relays.) Device function numbers readily identify devices in drawings, diagrams, instruction books, publications and specifications. The use of “52” for circuit breakers, “51” for an ac time overcurrent relay, “65” for a governor, and “86” for a lockout relay provides a simple brief method of designating the device’s operational performance. Table 10-2 indicates the usual pickup parameters for relays found in substation switchgear.


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Table 10-2. Relay pickup parameters Device no. Function Parameter settings

21 Distance Ohmic reach/angle of maximum torque 25 Synchronism Maximum closing (phase) angle/closing time 27 Undervoltage Undervoltage pickup 32 Directional power Power pickup and direction 49 Thermal Temperature pickup 50 Instantaneous overcurrent Instantaneous overcurrent pickup 51 Time overcurrent Time overcurrent pickup 59 Overvoltage Overvoltage pickup 63 Pressure Pressure pickup 67 Directional current Per 50 and 51 and direction 81 Frequency Frequency pickup 86 Lockout Lockout/reset features 87 Differential Differential settings


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d. Pictures 10-1 and 10-2 show an electromechanical relay and a solid-state relay respectively.

10-3. Installation-Wide Operating Systems. Systems include supervisory control and data acquisition (SCADA) systems and digitally-controlled Air Force switchgear systems. Perform maintenance in accordance with Operations and Maintenance Manuals furnished with the systems. Pictures 10-3 and 10-4 show installation-wide operating systems.

10-4. Protective Sensing, Processing, and Action Device EPM Reports. Each installation should prepare local blank EPM report forms to be filled out by the inspecting technicians. (See Paragraph 1-4.) The following tables indicate data which may need to be recorded. Evaluate the extent of data required based on your installation needs and maintenance ability.

a. Basic Assembly Information To Be Determined Before the Inspection. Provide a suitable record header with blank spaces for insertion of the following data given in Table 10-3.

Table 10-3. Device general data Designation Date of inspection Location Serial no. Year installed

Last inspection date Manufacturer Instruction manual Device type


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Picture 10-1 Plunger-type electromechanical relay

Picture 10-2 Solid-state relay


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Picture 10-3 SCADA controls

Picture 10-4 Digitally controlled Air Force switchgear


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b. Basic Inspection Items to Be Checked. Provide an inspection listing with column headings covering items to be checked off for each listed number given in Table 3-4.

c. Inspection Items To Be Covered. Table 10-1 indicates relay tests and appropriate criteria. Table 10-4 indicates instrument, metering, and protective relay general checks. For specific repairs and replacements see the manufacturer’s maintenance instructions.

Table 10-4. Instrument, metering, and protective relay general checks

Cleanliness Connections Calibration Multipliers Alignment Damage

Freedom of movement Contacts

Gasketing Targets Bearing

Operation JOHN W. HANDY, Lt General, USAF DCS/Installations & Logistics


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