01 - Overview of Protection Fundamentals

8/17/2019 01 - Overview of Protection Fundamentals

http://slidepdf.com/reader/full/01-overview-of-protection-fundamentals 1/28

INTRODUCTION TO

POWER SYSTEM PROTECTON



APPS- Combined course

Overview Of Protection Fundamentals

of 28

OVERVIEW OF PROTECTION FUNDAMENTALS

1.0 INTRODUCTION

Relays are compact devices that are connected throughout the power system todetect intolerable or unwanted conditions within an assigned area. They are ineffect, a form of active insurance designed to maintain a high degree of servicecontinuity and limit equipment damage. They are “Silent Sentinels”. Whileprotective relays will be the main emphasis of this chapter, other types of relays,applied on a more limited basis or used as part of a total protective relays system

will also be covered.

2.0

CLASSIFICATION OF RELAYS

Relays can be divided into five functional categories:

a. Protective Relays

, which detect defective lines, defective apparatus, or otherdangerous or intolerable conditions. These relays can either initiate or permitswitching or simply provide an alarm.

b.

Monitoring Relays, which verify conditions on the power system or in theprotection system. These relays include fault detectors, alarm units, channel-monitoring relays, synchronism verification, and network phasing. Powersystem conditions that do not involve opening circuit breakers during faults canbe monitored by these relays.

c. Programming Relays, which establish or detect electrical sequences.Programming relays are used for reclosing and synchronising.

d.

Regulating Relays, which are activated when an operating parameter deviatesfrom predetermined limits. Regulating relays function through supplementaryequipment to restore the quantity to the prescribed limits.

e.

uxiliary Relays, which operate in response to the opening or closing of theoperating circuit to supplement another relay or device. These include timers,

© AREVA T&D India Limited, Energy Automation & Information





of 28

contact-multiplier relays, sealing units, receiver relays, lock-out relays, closingrelays and trip relays.

In addition to these functional categories, relays may be classified by input,operating principle or structure and performance characteristic:

i) Input

Current

Voltage Power

Pressure Frequency Temperature

Flow

Vibration

ii)

Operating Principle of Structure

Percentage Multi-restraint Product Solid state Electromechanical

Thermal.

The above classification and definitions are based on the ANSI Standard 37.90(IEEE 313).

3.0 PROTECTIVE RELAYING SYSTEMS AND THEIR DESIGN

Technically, most relays are small systems within themselves. Throughout thischapter, however, the term systems will be used to indicate a combination ofrelays of the same or different types. Properly speaking, the protective relayingsystem includes circuit breakers as well as relays. Relays and circuit breakers mustfunction together; there is little or no value in applying one without the other.

Protective relays or systems are not required to function during normal powersystem operation, but must be immediately available to handle intolerable systemconditions and avoid serious outages and damage. Thus, the true operating life






of 28

of these relays can be on the order of a few seconds, even though they areconnected in a system for many years. In practice, the relays operate far moreduring testing and maintenance than in response to adverse service conditions.

In theory, a relay system should be able to respond to the infinity of abnormalitiesthat can possibly occur within the power system. In practice, the relay engineermust arrive at a compromise based on the four factors that influence any relayapplication:

a. Economics - Initial, operating and maintenance.b.

vailable measure of fault or t ouble

- Fault magnitudes and location of currenttransformers and voltage transformers.

r

c. Operating practices - Conformity to standard and accepted practices; ensuring

efficient system operation.d.

Previous experience

- History and anticipation perhaps better expressed oftrouble likely to be encountered within the system.

The third and fourth considerations are perhaps better expressed as the“personality of the system and the relay engineer”.

Since it is simply not feasible to design a protective relaying system capable ofhandling any potential problem, compromises must be made. In general, onlythose problems, which according to past experience are likely to occur, receive

primary consideration. Naturally, this makes relaying somewhat of an art. Differentrelay engineers will, using sound logic, design significantly different protectivesystems for essentially the same power system. As a result there is littlestandardisation in protective relaying. Not only may the type of relaying systemvary, but also will the extent of the protective coverage. Too much protection isalmost as bad as little.

Nonetheless, protective relaying is a highly specialised technology requiring an in-depth understanding of the power system as a whole. The relay engineer mustknow, not only the technology of the abnormal, but have a basic understanding ofall the system components and their operation in the system. Relaying, then, is a“Vertical” specialty requiring a “horizontal” viewpoint. This horizontal, or totalsystem, concept of relaying includes fault protection and the performance of theprotection system during abnormal system operation such as severe overloads,generation deficiency, out-of-step conditions, and so forth. Although these areas






of 28

are vitally important to the relay engineer, his concern has not always been fullyappreciated or shared by his colleagues. For this reason, close and continuedcommunication between the planning, relay design, and operation systems shouldbe mandatory, since power systems grow and operating conditions change.

A complex relaying system may result from poor system design or the economicneed to use fewer circuit breakers. Considerable savings can be realized by usingfewer circuit breakers and a more complex relay system. Such systems usuallyinvolve design compromises requiring careful evaluation, if acceptable protectionis to be maintained.

4.0

DESIGN CRITERIA

The application logic of protective relays divides the power system into severalzones, each requiring its own group of relays. In all cases, the five design criterialisted below are common to any well-designed and efficient protective system orsystem segment:

a. Reliability – the ability of the relay or relay system to perform correctly whenneeded (dependability) and to avoid unnecessary operation (security).

b. Speed – minimum fault time and equipment damage.c. Selectivity – maximum service continuity with minimum system disconnection.d.

Economics – maximum protection at minimum cost.

e.

Simplicity – minimum equipment and circuitry.

Since it is impractical to fully satisfy all these design criteria simultaneously thenecessary compromises must be evaluated on the basis of comparative risks.

4.1

Reliability

System reliability consists of two elements – dependability and security.Dependability is the certainty of correct operation in response to system trouble,while security is the ability of the system to avoid mis-operation between faults.Unfortunately, these aspects of reliability tend to counter one another: increasingsecurity tends to decrease dependability and vice versa. In general, however,modern relaying systems are highly reliable and provide practical compromisebetween security and dependability.






of 28

Protective relay system must perform correctly under adverse system andenvironmental conditions. Regardless of whether other systems are momentarilyblinded during this period, the relays must perform accurately and dependably.They must either operate in response to trouble in their assigned area or blockcorrectly if the trouble is outside their designated area.

Dependability can be checked relatively easily in the laboratory or duringinstallation by simulated tests or staged faults. Security on the other hand is muchmore difficult to check. A true test of system security would have to measureresponse to an almost infinite variety of potential transients and counterfeit troubleindications in the power system and its environment. A secure system is usually theresult of a good background in design combined with extensive miniature powersystem testing and can only be confirmed in the power system itself and its

environment.

4.2 Speed

Relays that could anticipate a fault would be utopian. But, even if available, theywould doubtlessly raise the question of whether or not the fault or trouble reallyrequired a trip-out. The development of faster relays must always be measuredagainst the increased probability of more unwanted or unexplained operations.Time, no matter how short, is still the best method of distinguishing between realand counterfeit trouble.

Applied to a relay, high speed indicates that the operating time usually does notexceed 50 ms (3 cycles on a 60-hertz base). The term instantaneous indicates thatno delay is purposely introduced in the operation. In practice, the terms highspeed and instantaneous are frequently used interchangeably.

4.3 Selectivity versus Economics

High speed relays provide greater service continuity by reducing fault damageand hazards to personnel. These relays generally have a higher initial cost,which, however, cannot always be justified. Consequently, both low and high-speed relays are used to protect power systems. Both types have high reliabilityrecords. Records on protective relay operations consistently show 99.5% andbetter relay performance.

4.4 Simplicity






of 28

As in any other engineering discipline, simplicity in a protective relay system isalways the hallmark of a good design. The simplest relay system, however, is notalways the most economical. As previously indicated, major economies arepossible with a complex relay system that uses a minimum number of circuitbreakers. Other factors being equal, simplicity of design improves systemreliability – if only because there are fewer elements that can malfunction.

5.0

FACTORS INFLUENCING RELAY PERFORMANCE

Relay performance is generally classed as:

(1) Correct(2) No conclusion

(3)

Incorrect

Incorrect operation may be either failure to trip or false tripping. The cause ofincorrect operation may be, a) Wrong application, b) Incorrect settings, c) Apersonnel error or 4) Equipment mal-function. Equipment that can cause anincorrect operation includes current transformers, voltage transformers, circuitbreakers, cable and wiring, relays, channels or station batteries.

Incorrect tripping of circuit breakers not associated with the trouble area is often asdisastrous as a failure to trip. Hence, special care must be taken in both

application and installation to ensure against the possibility of incorrect tripping.

“ No conclusion” is the last resort when no evidence is available for a correct orincorrect operation. Quite often this is a personnel involvement.6.0 Zones of Protection The general philosophy of relay application is to divide the power system intoprotective zones that can be protected adequately with the minimum amount of thesystem disconnected. The power system is divided into protective zones for:

i)

Generatorsii)

Transformersiii)

Busesiv)

Transmission and distribution circuitsv) Motors






of 28

A typical power system and its zones of protection are shown in Fig1. Thepurpose of the protective system is to provide the first line of protection, within theguide-lines outlined above. Since failures do occur, however some form of backupprotection is provided to trip out the adjacent breakers or zones surrounding thetrouble area. Protection in each zone is overlapped to avoid the possibility ofunprotected areas

7.0

PPLYING PROTECTIVE RELAYS

The first step in applying protective relays is to state the protection problemaccurately. Although developing a clear, accurate statement of the problem canoften be the most difficult part, the time spent will pay dividends – particularlywhen assistance from others is desired. Information on the following associated or

supporting areas in necessary.

a. System configurationb.

Existing systems protection and its difficultiesc.

Existing operating procedures and practices; possible future expansionsd. Degree of protection requirede. Fault studyf.

Maximum load and current transformer ratiosg. Voltage transformer locations, connections and ratiosh.

Impedance of the lines and transformers.

7.1 System Configuration

System configuration is represented by a single line diagram showing the area ofthe system involved in the protection problem. This diagram should show in somedetail the location of the breakers, the bus arrangements, the taps on lines & theircapacity, the location & size of the generation, the location, size & connections ofthe power transformers and the system frequency.

Transformer connections are particularly important. For ground relaying, thelocation of the ground sources must also be known.

7.2

Existing systems Protection and Procedures

The existing protective equipment and the reasons for the desired changes shouldbe outlined. Difficulties with the present relaying system are a valuable guide toimprovements. New installations should be so specified. As new relay system






of 28

will often be required to operate with or utilize parts of the existing relaying,details on these existing systems are important.

Wherever possible, changes in system protection should conform to existingoperating procedures and practices. Exceptions to standard procedures tend toincrease the risk of personnel error and may disrupt the efficient operation of thesystem. Anticipated system expansions can also greatly influence the choice ofprotection.

7.3

Degree of Protection Required

To determine the degree of protection required, the general type of protectionbeing considered should be outlined, together with the system conditions oroperating procedures and practices that will influence the final choice. These data

will provide answer to the following types of questions. Is pilot, high-speed,medium, or slow-speed relaying required? Is simultaneous tripping of all breakersof a transmission line desired? Is instantaneous reclosing needed?

7.4

Fault Study

An adequate fault study is necessary in almost all relay applications. Three-phasefaults, line-to-ground faults and line-end faults should all be included in the study.Line-end fault data are important in cases where one breaker may operate aheadof another. For ground relaying, the fault study should include zero sequencevoltage and negative sequence currents and voltages. These quantities are easily

obtained during the course of a fault study and are often extremely useful insolving a difficult relaying problem.

7.5

Maximum Loads, Transformer Data and Impedance

Maximum load current, potential transformer connections, its ratios and locationsare required for proper relay application. Maximum loads should be consistentwith the fault data and should be based on the same system conditions. Line andtransformer impedance should also be known. Phase sequence should bespecified if three-line connection drawings are involved.

Obviously, not all the above data are necessary in every application. It isdesirable, however, to at least review the system with respect to the above pointsand wherever applicable, to compile necessary data.






of 28

In any event, no amounts of data can ensure a successful relay application unlessthe protection problems are first defined. In fact, the application problem isessentially solved when the available measures (handles) for distinguishingbetween tolerable and intolerable conditions can be identified and specified.

8.0 ELECTRICAL POWER SYSTEM DEVICE NUMBERS AND FUNCTIONS

The device switching equipment are referred to by numbers, with appropriatesuffix letters when necessary, according to the functions they perform.

These numbers are based on a system adopted as standard for automaticswitchgear by IEEE and incorporated in American Standard C37.2 – 1970. This

system is used in connection diagrams, in instruction books and in specifications.

8.1

Device Numbering

Device Number Definition Function

1 Master Element It is an initiating device, such as acontrol switch, voltage relay, floatswitch, etc., which serves either directlyor through such permissive devices asprotective and time delay relays.to place an equipment in or out ofoperation.

2 Time DelayStarting orClosing Relay

It is a device which functions to give adesired amount of time delay before orafter any point of operation in a

switching sequence or protectiverelaying system, except as specificallyprovided by device function 48, 62 and79 described later.

3 Checking orInterlocking Relay

It is a device which operates in responseto the position of a number of other






of 28


devices (or to a number ofpredetermined conditions), in an

equipment, to allow an operatingsequence to proceed, to stop, or toprovide a check of the position of thesedevices or of these conditions for anypurpose.

4 Master Contactor It is a device, generally controlled by thedevice No.1 or equivalent, and therequired permissive and protectivedevices, that serve to make and breakthe necessary control circuits to place an

equipment into operation under thedesired conditions and to take it out ofoperation under other or abnormalconditions.

5 Stopping Device It is a control device used primarily toshut down an equipment and hold it outof operation. This device may bemanually or Electrically actuated, butexcludes the function of electrical lockout(see device function 86) on abnormal

conditions.6 Starting Circuit

BreakerIt is a device whose principal function isto connect a machine to its source ofstarting voltage.

7 Anode CircuitBreaker

It is one used in the anode circuits of apower rectifier for the primary purposeof interrupting the rectifier circuit if anarc back should occur.

8 Control Power

DisconnectingDevice

It is a disconnecting device – such as a

knife switch, circuit breaker or pulloutfuse block, used for the purpose ofconnecting and disconnecting the sourceof control power to and from the controlbus or equipment.Note: Control power is considered to






of 28


include auxiliary power, which suppliessuch apparatus as small motors and

heaters.9 Reversing Device It is used for the purpose of reversing amachine field or for performing anyother reversing functions.

10 Unit SequenceSwitch

It is used to change the sequence inwhich units may be placed in and out ofservice in multiple – unit equipment.

11 Reserved for futureapplication

12 Over–Speed

Device

It is usually a direct connected speed

switch which functions on machine over–speed.

13 SynchronisedSpeed Device

A centrifugal speed switch, a slipfrequency relay, a voltage relay, anundercurrent relay or any type of devicethat operates at approximatelysynchronous speed of a machine.

14 Under SpeedDevice

It is a device, which functions when thespeed of a machine falls below apredetermined value.

15 Speed orFrequencyMatching Device

It is a device that functions to match andhold the speed or the frequency of amachine or of a system equal to, orapproximately equal to, that of anothermachine, source or system.


17 Shunting orDischarge Switch

It serves to open or to close a shuntingcircuit around any piece of apparatus

(Except a resistor), such as a machinefield, a machine armature, a capacitoror a reactor.Note: This excludes devices whichperform such shunting operation as maybe necessary in the process of starting a






of 28


machine by devices 6 or 42 or they’reequivalent, and also exclude device 73

function which serves for the switching ofresistors.18 Accelerating or

DeceleratingDevice

It is used to close or to cause the closingof circuits, which are used to increase orto decrease the speed of a machine.

19 Starting-To-Running TransitionContactor

It is a device, which operates to initiateor cause the automatic transfer of amachine from the starting to the runningpower connection.

20 Electrically

operated Valve

It is an electrically operated, controlled

or monitored valve in a fluid line.Note: The function of the valve may beindicated by the use of the suffixes.

21 Distance Relay It is a device, which functions when thecircuit admittance impedance orreactance increases or decreasesbeyond predetermined limits.

22 Equaliser CircuitBreaker

It is a breaker, which serves to control orto make and break the equaliser or thecurrent–balancing connections for amachine field, or for regulatingequipment, in a multiple-unit of theinstallation.

23 TemperatureControl Device

It is a device to raise or lower thetemperature of a machine or otherapparatus or of any medium, when itstemperature falls below, or rises above,a predetermined value.Note: An example is a thermostat which

switches on a space heater in aswitchgear assembly when thetemperature falls to a desired value asdistinguished from a device which isused to provide automatic temperatureregulation between close limits and






of 28


would be designated as 90T.24 Reserved for future

application25 Synchronising orSynchronism–Check Device

It is a device that operates when two accircuits are within the desired limits offrequency, phase angle and voltage, topermit or to cause the paralleling ofthese two circuits.

26 ApparatusThermal Device

It is a device, which functions when thetemperature of the shunt field or thearmature winding of a machine, or thatof a load limiting or load shifting resistor

or of a liquid or other medium exceeds apredetermined value ; or if thetemperature of the protected apparatus,such as a power rectifier, or of anymedium decreases below apredetermined value.

27 Under VoltageRelay

It is a device, which functions on a givenvalue of undervoltage.

28 Flame detector It is a device that monitors the presenceof the pilot or main flame in suchapparatus as a gas turbine or a steamboiler.

29 IsolatingContactor

It is a device used for disconnecting onecircuit from another for the purposes ofemergency operation, maintenance, ortest.

30 Annunciator relay It is a non-automatically reset device thatgives a number of separate visualindications upon the functioning of

protective devices and which may alsobe arranged to perform a lockoutfunction.

31 SeparateExcitation Device

It connects a circuit such as the shuntfield of a synchronous converter, to asource of separate excitation during the






of 28


starting sequence ; or one whichenergises the excitation and ignition

circuits of a power rectifier.32 Directional PowerRelay

It is a device which functions on adesired value of power flow in a givendirection, or upon reverse power, likeresulting from arc back in the anode orcathode circuits of a power rectifier.

33 Position Switch It makes or breaks contact when themain device or piece of apparatus,which has no device function number,reaches a given position.

34 Master SequenceDevice

It is a device such as a motor-operatedmulti-contact switch, or the equivalent, ora programming device, such as acomputer, that establishes or determinesthe operating sequence of the majordevices in an equipment during startingand stopping or during other sequentialoperations.

35 Brush–Operating,or Slip-ring-short-circuiting Device

It is used for raising, lowering, orshifting, the brushes of a machine, or forshort circuiting its slip rings, or forengaging or disengaging the contacts ofa mechanical rectifier.

36 Polarity orPolarising VoltageDevice

It operates or permits the operation ofanother device on a predeterminedpolarity only or verifies the presence of apolarising voltage in an equipment.

37 Undercurrent orUnder power

Relay

It functions when the current or powerflow decreases below a predetermined

value.38 Bearing ProtectiveDevice

It functions on excessive bearingtemperature, or on other abnormalmechanical conditions, such as unduewear, which may eventually result inexcessive bearing temperature.






of 28


39 MechanicalCondition Monitor

It is a device that functions upon theoccurrence of abnormal mechanical

conditions, (except that associated withbearings as covered under devicefunction 38), such as excessive vibration,eccentricity, expansion, shock, tilting, orseal failure.

40 Field Relay It functions on a given or abnormally lowvalue or failure of machine field current,or on an excessive value of the reactivecomponent of armature current in an acmachine indicating abnormally low field

excitation.41 Field Circuit

BreakerIt is a device, which functions to apply,or to remove the field excitation of amachine.

42 Running CircuitBreaker

It is a device whose principal function isto connect a machine to its source ofrunning or operating voltage. Thisfunction may also be used for a device,such as a contactor, that is used in serieswith a circuit breaker or other fault

protecting means, primarily for frequentopening and closing of the circuit.

43 Manual Transferor Selector Devicetransfers

It transfers the control circuits so as tomodify the plan of operation of theswitching equipment or of some of thedevices.

44 Unit SequenceStarting Relay

It is a device, which functions to start thenext available unit in a multiple-unitequipment on the failure or on the non-

availability of the normally precedingunit.45 Atmospheric

Condition MonitorIt is a device that functions upon theoccurrence of an abnormal atmosphericcondition, such as damaging fumes,explosive mixture, smoke or fire.






of 28


46 Reverse–Phase,Phase–Balance,

Current Relay

It is a relay which functions when thepoly-phase currents are of reverse phase

sequence, or when the poly-phasecurrents are unbalanced or containnegative phase–sequence componentsabove a given amount.

47 Phase – Sequence Voltage Relay

It functions upon a predetermined valueof poly phase voltage in the desiredphase sequence.

48 IncompleteSequence Relay

It is a relay that generally returns theequipment to the normal, or off, positionand locks it out if the normal starting,

operating or stopping sequence is notproperly completed within apredetermined time. If the device is usedfor alarm purpose only, it shouldpreferably be designated as 48A(alarm).

49 Machine, orTransformer,Thermal Relay

It is a relay that functions when thetemperature of a machine armature, orother load carrying winding or elementof a machine, or the temperature of a

power rectifier or power transformer(including a power rectifier transformer)exceeds an predetermined value.

50 Instantaneousovercurrent, orRate of rise Relay

It is a relay that functions instantaneouslyon an excessive value of current, or onan excessive current rise, thus indicatinga fault in the apparatus or circuit beingprotected.

51 AC Time

Overcurrent Relay

It is a relay with either a definite or an

inverse time characteristic that functionswhen the current in an ac circuit exceedsa predetermined value.

52 AC CircuitBreaker

It is a device that is used to close andinterrupt an ac power circuit undernormal conditions or to interrupt this






of 28


circuit under fault or emergencyconditions.

53 Exciter orGenerator Relay It is a relay that forces the dc machinefield excitation to build up duringstarting or which functions when themachine voltage has build up to a givenvalue.

54 Reserved for futureapplication.

55 Power FactorRelay

It is a relay that operates when thepower factors in an ac circuit risesabove or below a predetermined value.

56 Field ApplicationRelay

It is a relay that automatically controlsthe application of the field excitation toan ac motor at some predeterminedpoint in the slip cycle.

57 Short – Circuitingor GroundingDevice

It is a primary circuit switching devicethat functions to short-circuit or to grounda circuit in response to automatic ormanual means.

58 RectificationFailure Relay

It is a device that functions if one ormore anodes of a power rectifier fail tofire, or to detect an arc-break or failureof a diode to conduct or block properly.

59 Overvoltage Relay It is a relay that functions on a givenvalue of overvoltage.

60 Voltage or CurrentBalance Relay

It is a relay that operates on a givendifference in voltage, or current input oroutput of two circuits.


62 Time – DelayStopping oropening Relay

It is a time delay relay that serves inconjunction with the device that initiatesthe shutdown, stopping, or openingoperation in an automatic sequence.

63 Pressure Switch It is a switch, which operates on givenvalues or on a given rate of change of






of 28


pressure.64 Ground Protective

Relay

It is a relay that functions on failure of

the insulation of a machine, transformeror of other apparatus to ground, or onflashover of a dc machine to ground. Note: This functions is assigned only to arelay which detects the flow of currentfrom the frame of a machine orenclosing case or structure of a piece ofapparatus to ground, or detects aground on a normally ungroundedwinding or circuit. It is not applied to

device connected in the secondarycircuit or secondary neutral of a currenttransformer, or in the secondary neutralof current transformer, connected in thepower circuit of a normally groundedsystem.

65 Governor It is the assembly of fluid, electrical, ormechanical control, equipment used forregulating the flow of water, steam, orother medium to the prime mover for

such purpose as starting, holding orstopping speed load.

66 Notching or Jogging Device

It functions to allow only a specifiednumber of operations of a given device,or equipment, or a specified number ofsuccessive operations within a given timeof each other. It also functions toenergise a circuit periodically or forfractions of specified time intervals, or

that is used to permit intermittentacceleration or jogging of a machine atlow speeds for mechanical positioning.

67 AC directionalOvercurrent Relay

It is a relay that functions on a desiredvalue of ac overcurrent flowing in apredetermined direction.






of 28


68 Blocking Relay It is a relay that initiates a pilot signal forblocking of tripping on external faults in

a transmission line or in other apparatusunder predetermined conditions, or co-ordinates with other devices to blocktripping or to block re-closing on an out-of-step condition or on power swings.

69 Permissive ControlDevice

It is generally a two position, manuallyoperated switch that in one positionpermits the closing of a circuit breaker,or the placing of an equipment intooperation, and in the other position

prevents the circuit breaker or theequipment from being operated.

70 Rheostat It is a variable resistance device used inan electric circuit, which is electricallyoperated or has other electricalaccessories, such as auxiliary position orlimit switches.

71 Level Switch It is a switch which operates on givenvalues, or on a given rate of change, oflevel.

72 DC circuit Breaker It is used to close and interrupt a dcpower circuit under normal conditions orto interrupt this circuit under fault oremergency conditions.

73 Load – ResistorContactor

It is used to shunt or insert a step of loadlimiting, shifting, or indicating resistancein a power circuit, or to switch a spaceheater in circuit, or to switch a light, orregenerative load resistor of a power

rectifier or other machine in and out ofcircuit.74 Alarm Relay It is a device other than the annunciator,

as covered under device No.30, whichis used to operate in connection with avisual or audible alarm.






of 28


75 Position ChangingMechanism

It is a mechanism that is used for movinga main device from one position to

another in an equipment ;as forexample, shifting a removable circuitbreaker unit to and from the connected,disconnected, and test positions.

76 DC OvercurrentRelay

It is a relay that functions when thecurrent in a dc circuit exceeds a givenvalue.

77 Pulse Transmitter It is used to generate and transmit pulsesover a telemetering or pilot-wire circuit tothe remote indicating or receiving

device.78 Phase Angle

Measuring, or out-of-step ProtectiveRelay

It is a relay that functions at apredetermined phase angle between twovoltages or between two currents orbetween voltage and current.

79 AC Re-closingRelay

It is a relay that controls the automaticreclosing and locking out of an ac circuitinterrupter.

80 Flow Switch It is a switch, which operates on givenvalues, or on a given rate of change, offlow.

81 Frequency Relay It is a relay that functions on apredetermined value of frequency, eitherunder/over on normal system frequencyor rate of change of frequency.

82 DC Re-closingRelay

It is a relay that controls the automaticclosing and reclosing of a dc circuitinterrupter, generally in response to loadcircuit conditions.

83 AutomaticSelective Controlor Transfer Relay

It is a relay that operates to selectautomatically between certain sources orconditions in an equipment, or performsa transfer operation automatically.

84 OperatingMechanism

It is the complete electrical mechanism orservo-mechanism, including the






of 28


operating motor, solenoids, positionswitches, etc., for a tap changer,

induction regulator or any similar pieceof apparatus which has no devicefunction number.

85 Carrier or Pilot-wire ReceiverRelay

It is a relay that is operated or restrainedby a signal used in connection withcarrier-current or dc pilot-wire faultdirectional relaying.

86 Locking–out Relay It is an electrically operated, hand orelectrically reset, relay that functions toshut down and hold an equipment out of

service on the occurrence of abnormalconditions.

87 DifferentialProtective relay

It is a protective relay that functions on apercentage or phase angle or otherquantitative difference of two currents orof some other electrical quantities.

88 Auxiliary Motor orMotor Generator

It is one used for operating auxiliaryequipment such as pumps, blowers,exciters, rotating magnetic amplifiers,etc.

89 Line Switch It is used as a disconnecting load interrupter, or isolating switch in an acor dc power circuit, when this device iselectrically operated or has electricalaccessories, such as an auxiliary switch,magnetic lock, etc.

90 Regulating Device It functions to regulate a quantity, orquantities, such as voltage, current,power, speed, frequency, temperature,

and load, at a certain value or betweencertain (generally close) limits formachines, toe lines or other apparatus.

91 VoltageDirectional Relay

It is a relay that operates when thevoltage across an open circuit breaker orcontactor exceeds a given value in a






of 28


given direction.92 Voltage and

power DirectionalRelay

It is a relay that permits or causes the

connection of two circuits when thevoltage difference between themexceeds a given value in apredetermined direction and causesthese two circuits to be disconnectedfrom each other when the power flowingbetween them exceeds a given value inthe opposite direction.

93 Field changingContactor

It functions to increase or decrease inone-step the value of field excitation on a

machine.94 Tripping or Trip-

free RelayIt functions to trip a circuit breaker,contactor, or equipment, or to permitimmediate tripping by other devices ; orto prevent immediate re-closure of acircuit interrupter, in case it should openautomatically even though its closingcircuit is maintained closed.

95 Used only forspecificapplications onindividualInstallations wherenone of theassignednumberedfunctions from 1 to94 is suitable.

8.2

Devices Performing More Than One Function

If one device performs two relatively important functions in an equipment so that itis desirable to identify both of these functions, this may be done by using a doublefunction number and name such as:






of 28

50/51 - Instantaneous and Time Overcurrent Relay.

8.3

Suffix Numbers

If two or more devices with the same function number and suffix letter (if used) arepresent in the same equipment, they may be distinguished by numbered suffixes asfor example, 52X-1, 52X-2 and 52X-3, when necessary.

8.4

Suffix Letters

Suffix letters are used with device function numbers for various purposes. In orderto prevent possible conflict each suffix letter should have only one meaning in anindividual equipment. All other words should use the abbreviations as contained in ANSI Y1.1 latest revision, or should use some other distinctive abbreviation, or bewritten out in full each time they are used. The meaning of each single suffix letter,

or combination of letters, should be clearly designated in the legend on thedrawings or publications applying to the equipment.

Lower case (small) suffix letters are used in practically all instances on electricaldiagrams for the auxiliary, position, and limit switches. Capital letters aregenerally used for all other suffix letters. The letters should generally form part ofthe device function designation, are usually written directly after the devicefunction number, as for example, 52CS, 71W, or 49D. When it is necessary touse two types of suffix letters in connection with one function number, it is oftendesirable for clarity to separate them by a slanted line or dash, as for example,

20D/CS or 20D-CS.

The suffix letters which denote parts of the main device, and those which cannot orneed not form part of the device function designation, are generally written directlybelow the device function number on drawings, as for example, 52/CC or 43/A.

8.9

Standard reference positions of some typical devices

Device Standard Reference Position

Power Circuit Breaker Main Contacts OpenDisconnecting Switch Main Contacts OpenLoad-break switch Main Contacts Open Valve Closed PositionGate Closed PositionClutch Disengaged Position






of 28

Turning Gear Disengaged PositionPower Electrodes Maximum Gap PositionRheostat Maximum resistance Position

Adjusting Means (1) Low or Down PositionRelay (2) De-energised PositionContactor (2) De-energised PositionContactor (latched-in-type) Main Contacts OpenTemperature Relay (3) Lowest TemperatureLevel Detector (3) Lowest LevelFlow Detector (3) Lowest FlowSpeed Switch (3) Lowest Speed Vibration Detector (3) Minimum VibrationPressure Switch (3) Lowest Pressure

Vacuum Switch (3) Lowest Pressure i.e., Highest VacuumNote : If several similar auxiliary switches are present on the same device, they should bedesignated numerically 1,2,3 etc, when necessary.

(1) These may be speed, voltage, current, load, or similar adjusting devices comprising rheostats,springs, levers, or other components for the purpose.

(2) These electrically operated devices are of the non-latched-in type, whose contact position isdependent only upon the degree of energisation of the operating or restraining or holding coilor coils which may or may not be suitable for continuous energisation. The de-energisedposition of the device is that with all coils de-energised.

(3) The energising influences for these devices are considered to be, respectively, risingtemperature, rising level, increasing flow, rising speed, increasing vibration, and increasingpressure.

The simple designation “a” or “b” is used in all cases where there is no need toadjust the contacts to change position at any particular point in the travel of themain device or where the part of the travel, where the contacts change position isof no significance in the control or operating scheme. Hence the ”a” or “b”designations usually are sufficient for circuit breaker auxiliary switches.9.0

CLASSIFICATION OF RELAYS ON TECHNOLOGY

Protective relays can be classified into two main categories on the technology oftheir design,

1.

Electromechanical






of 28

2.

Static.

In practice these terms are used loosely and ends up being wrongly interpretedand understood. Though the reason for these different types of relays is thecontinuous change in electronic technology, each of these types have their owndistinct advantage over the other.

9.1

Electromechanical Relays

Electromechanical relays are defined as “Protective relays using magneto motiveforce for their operation. Their measuring elements have moving parts”. Hingedarmature, Disc relays are very good examples of Electromechanical technology.

9.2 Static Relays

Static relays are defined as “Protective relays without any moving parts in themeasuring element”. Relays designed using electronics is a typical example forrelays under such category. It should be understood here that static relays can alsohave its output elements with moving parts (like miniature relays).

The static relays, as said above are mainly relays designed using electronics, thusdue to the evolution of electronics, the static relays also used different techniques intheir design as listed below,

Static Analogue Relays

Static Digital Relays Static Numerical Relays

9.21

Static Analogue Relays

Static relays designed using analogue electronic components fall under thiscategory. In such relays, the input signal after conditioning are directly fed toanalogue measuring elements, like comparators, for e.g., operational amplifiers.These devices compare the input analogue signal with the reference signal andgenerate an output signal depending on the value of the input signal.

9.22

Static Digital Relays

Static Relays designed using digital electronic components are classified under thiscategory. In these relays, the input analogue signals after conditioning areconverted into digital signals using Analogue to Digital (A/D) converters.. Thenthese digital signals are fed to digital comparators, which compare these signals






of 28

with their reference signals and produce an output. Depending on the number ofelements and phases required, these hardware comparators are provided.

9.23 Static Numerical Relays

Numerical relays are also digital relays. In these relays the input signal afterconditioning is digitised using A/D converters. These digitised signals are then fedinto the microprocessor directly. The entire protection element in numeric relays isrealised using software programs. These software called as application softwareare stored in non-volatile memory in the relay. The input signals are continuouslysampled and stored in the memory. Then these values are compared against theset threshold values (stored in the memory). The software statements perform theseoperations and generate the output. In numeric relays, the software statements dothe job done by hardware comparators or measuring elements in analogue and

digital relays.

Thus in numerical relays, multiple elements or phases of protection are realised byappropriately writing the software statements. This does not involve any physicaladdition in space. This is the reason why numerical relays are developed withmore than one protection integrated in them, as the cost involved in integration ofmore funcitons is very less.

Additionally, in numerical relays since the data is stored in the memory it can givelot of other information and features like, fault recording, event recording,

measurements, etc. The presence of microprocessors in the relay enables it tocommunicate with computers and provide self diagnostics function.

One more advantage of numerical relays is its capability to adapt itself to change.This at times is seen as a nuisance since a numerical relay undergoes lot ofaddition in functions and features in its life time.

The following Chart gives a birds-eye view of the relay classifications based ontechnology.


Electromechanical Static

Analogue Digital

Numerical

Relays





of 28

01 - Overview of Protection Fundamentals

Documents

Transcript of 01 - Overview of Protection Fundamentals