SIEMENS

PRESENTATION ON SUBSTATION DESIGN

ByYuvaraj PatilI&S/WR

SUBSTATION DESIGNWHAT IS THERE IN SUBSTATION DESIGNING ??

SLDEQUIPMENT LAYOUTBUSBAR ARRANGEMENTFAULT LEVELTYPE OF CONSTRUCTIONCREEPAGE AND CLEARANCEGROUNDING & LIGHTNING PROTECTIONSAFETY INTERLOCKSOTHERS, e.g. LIGHTING AND CIVIL

SUBSTATION DESIGN CRITERIAFOLLOWING STUDIES ARE PERFORMED TO ESTABLISH THE DESIGN CRITERIA FOR A SUBSTATION

1. LOAD FLOW STUDIES :- To determine the current carrying requirements of new s/s.- To determine the continuous and Emergency rating of equipment

2. S.C.CALCULATION :- To permit the equipment to without damage, severe thermal and mechanical stresses of S.C. currents.- To provide adequate interrupting capability in CBs, strength in post insulators- Setting of protective relays

SUBSTATION DESIGN CRITERIA3. TRANSIENT STABILITY STUDY : Following factors affects the Stability of System.- Severity of Fault- Speed with which fault is cleared- Ties between the Machine and the System after the fault are cleared ( Which may weaken the system by operating more than one line due to not operation of primary relaying )

4. TRANSIENT OVER VOLTAGE STUDY :- It is required to protect the equipments from Lightning Stroke and Switching Transient.-*-

SUBSTATION ARRANGEMENT ASPECTS1. System Security :- The ideal s/s is one where each circuit is controlled by separate CB with facility for replacement of bus bar OR CB in the event of fault or during maintenance.- Double Bus Bar system with Double CB arrangement is ideal.

2. Operational Flexibility :- For efficient loading of Generators it is necessary to control MVA and MVAR loading under all condition

3. Simplicity of Protection Arrangement :- Where greater no of CB has to be tripped during fault condition, protection arrangement becomes more complex.

JERP is best example of complex Protection !!

SUBSTATION ARRANGEMENT ASPECTS4. Ability to Limit the S.C. Levels :- Any arrangement which incorporates means of providing a S/S into Two separate sections is suitable to Limit S.C levels.

5. Maintenance Facilities :- Arrangement shall be suitable for the Planned or Emergency Maintenance .

6. Ease of Extension ::- To add new bays there shall be space and expansion facilities.

7. Site Considerations :- Where the area is limited, simple arrangement with least no of CBs.

Considerations for Choice of Busbar Arrangement

A number of factors are to be considered while finalizing the Layout and Switching arrangements of S/S.

Importance of SubstationReliabilityRedundancyEconomics and availability of financeAvailability of Space and Right Of Way for approaching linesFuture Expansion

Line IsolatorBusBus- IsolatorCircuit-breaker Earthing-switch Protection-zone, busbarProtection-zone, line/trafoLine 2Line 1Single Bus System- Primary Components, Protection ZoneCurrent TransformerPotential TransformerBus- Earthing SwitchBus- Potential TransformerWave TrapLine IsolatorEarthing-switch Wave TrapSurge arresterTransformer

Main & Transfer Bus ArrangementMain BusTransfer Bus couplerA Transfer Bus Coupler & All feeders need one additional isolator. In Thermax Project we are using this arrangementTransfer BusxLine 2Line IsolatorEarthing-switch Wave TrapSurge arresterTransfer IsolatorCTCTCTCT

Ring or Mesh SystemLine 1Line 2Transformer 1Transformer 2

Bus- disconnectCircuit-breaker CTVTLine- disconnectEarthing switch Bus Section-isolatorBus B Bus A Surge arresterEarthing switch Single Bus with sectionaliser System- Primary Components, Over-lapping Protection ZoneBus PT 1Bus PT 2To improve Reliability bus section isolator/CB is introduced

Bus- IsolatorsCircuit-breaker CTBus IBus IIBus-couplerDouble Main Bus System or Main & Reserve Bus systemLine IsolatorEarthing-switch TransformerLine IsolatorEarthing-switch Wave TrapSurge arresterLine 1 Earthing-switch Wave TrapSurge arresterLine 2 Bus- PT -IBus- PT -IIBus- Earthing-I, II

Bus- IsolatorsCircuit-breaker CTBus IBus IIBus-couplerDouble Main & Transfer Bus Arrangement (DMT)Line IsolatorEarthing-switch Wave TrapSurge arresterLine 1 Bus- PT -IBus- PT -IIBus- Earthing-I, IIEarthing-switch Wave TrapSurge arresterLine 2Transfer Bus-couplerTransfer IsolatorAlmost all PGCIL 220kV substations use this arrangement

Bus ABus BQ0 41Q0 42Q0 11Q0 13Q0 12For future useBushingBushingOne and a Half Breaker Arrangement

Almost all PGCIL 765kv,400kV substations use this arrangement

2000/1/1/1ACore Like line 417Three Main & Transfer Bus ArrangementPracticed in Europe, Germany

245 kV Outdoor switchyard (AIS) Double busbars, classical layout1 Bus I3 Bus-disconnector 5 CT 7 Line-disconnector with built-on earthing switch 2 Bus II4 Circuit-breaker 6 VT 8 Surge arrester245kV Switchyard Layout

Almost all PGCIL 220kV substations use this arrangement

SUBSTATION DESIGN CONSIDERATIONS

1. FAULT LEVEL : Expressed as MVA or kA and duration of 1-3 Sec. Depends on source impedance All CBs are to be rated for fault level Earth Switches for making fault level- All Bus bars, bus supports to be designed to withstand forces due to S.C

2. SAFETY CLEARANCES :

3. STRUCTURE :Why is it required ?To support and install Buses, electrical equipment and terminate transmission line conductors.The structures may be of steel, RCC or wood They need foundation according to soil condition at site

SUBSTATION DESIGN CONSIDERATIONS

Design of Structures are affected by :- Phase clearance- Ground clearance- Length and weight of buses and other equipment.Design Load on Girders shall include :- Conductor tension- Earth wire tension- Weight of Insulators and Hardwares- Erection load ( approx. 350 kg)- Weigh of man & tools to work ( aprox. 200kg)- Wind load- Impact load, if any during operation of equipment.- Walkway if any. ( BSP Project we are providing the same)

SUBSTATION DESIGN CONSIDERATIONS

Recommended Standard Bay Widths :

400kV feeder Bays - 27m400kV Transformer Bays - 20m ( per phase)220kV Feeder Bays- 17m110kV Feeder Bays- 10m110kV Transformer Bays - 10m 66kV Bays- 8m22kV Bays- 3.8m11kV Bays- 3.5m

SUBSTATION DESIGN CONSIDERATIONS

Normally adopted phase spacings are :

Sr. No.Voltage Level (kV) Spacing (m)111/221.32331.53662.0 to 2.2 41102.4 to 3.052204.564007.0

BUS DESIGNPresent day trend is to use Rigid bus rather than strain bus due to can be constructed at lower profile. are aesthetically pleasing. corona level is lower.Construction of Rigid Bus : Aluminum bus materials used for rigid bus may be of different shapes. They may be round tubing's, channels, angles or integral web designs. Round tubing used in all voltage levels.Square/channel tubing is used only at lower voltages.Angle bus used only at distribution voltages.Integral web bus is structurally strong and is used for high current and long spans generally at lower voltage.

BUS DESIGNDesign considerations of Rigid Bus :Bus must carry the expected maximum load current without exceeding the temp. limit .The capacity of bus shall be checked for max. temp. under S.C. conditions.Shall be designed to take vibration induced by the action of 50Hz current.Shall be designed to take the vibration due to wind flowing across the tubing. It should withstand the S.C. force. for HV and EHV S/S the diameter of bus should be checked for corona discharge. The bus support system must be capable to to take weight of tubing, damping material, wind on tubing, S.C. force calculated.

BUS DESIGN2. Design considerations of Strain Bus :

Widely used in most of the station due to ease of construction.Even in station where Rigid bus is predominant, some spans will be invariably of strain bus construction.The design followed is based on simple sag-tension calculations.The down drops from strain bus appear as a concentrated load.Depending on length and weight of dropper, tension on bus will vary considerably.Where bundled conductors are used in strain bus, the type of spacer may have an influence on resulting tension. If rigid spacers are used, then during S.C., the two conductors will attempt to draw together and cause increases tension on strain bus

ACCESSORIES REQUIRED FOR BUS CONSTRUCTIONRIGID BUS :BPIAluminium Tubular pipes for busWelding Sleeves of equivalent dia for Al Bus.BPI clamp for fixing tubular pipe to the insulatorInter connector for Al tube to strain BusCorona bells for the free ends of right bus.

STRAIN BUS :Insulator stringsACSR conductor of right choiceHardware fittings for tension points.Arcing hornsCorona rings

ACCESSORIES REQUIRED FOR BUS CONSTRUCTION6. Sag compensating spring.7. Suspension clamps with accessories for jumper connection points.8. Rigid or flexible spacers ( For bundle conductor bus)9. Parallel Groove clamps (PG Clamps) suitable for the ACSR for jumper and dropper connections.10. Tee Clamps for droppers. (With suitable sizes).11. Clamp to connect droppers, jumpers and interconnections to the equipment and on BPI

SUBSTATION EARTHINGPurpose :

In ungrounded system, it will be inherently coupled capacitively to the earth th system capacitance. During ground fault, the charging current will rise to 3 times the Zero sequence current, develops high value of voltage.

so earthing is required to

Limit the transient overvoltages caused by restricting the ground current.Safety to the personnel working in the maintenance.Fast and selective clearing of ground fault to limit the damage to the equipment.

SUBSTATION EARTHINGFollowing steps are involved in Design of Earthing System.

Soil investigation.Determination of maximum ground currentPreliminary designing of grounding systemCalculation of resistance of grounding systemCalculation of maximum grid potential rise.Calculation of step and touch voltages.Correction of preliminary design.A continuous earth conductor is placed around the perimeter of yard to enclose as much ground as possible to avoid current concentration.Within the grid conductors are laid in parallel lines and at uniform spacing along the rows of structure and equipment.

SUBSTATION EARTHINGThe earthing material should have

High conductivity Low underground corrosion

GI material is used for earthing and size of conductor should be such thatIt has thermal stability to flow the ground fault currentIt should last at least for 50 years without causing break in the ground circuit due to corrosionIt should be mechanically strong.

INSTRUMENT TRANSFORMERInstrument Transformers are used to provide the exact proportion of the high voltage and current within the substation at a level suitable for metering, relaying and control.Voltage Transformers :VT may be of Electromagnetic or Capacitor type.When high level of accuracy is required then Electromagnetic type is used.All voltage transformers are required to comply with one of the classes in Table 8.1.

VOLTAGE TRANSFORMERFor protection purposes, accuracy of voltage measurement may be important during fault conditions, as the system voltage might be reduced by the fault to a low value. Voltage transformers for such types of service must comply with the extended range of requirements set out in table 8.2

VOLTAGE TRANSFORMERVoltage Factors :The value Vf in Table 8.2 is an upper limit of operating voltage, expressed in per unit of rated voltage. This is important for correct relay operation and operation under unbalanced fault conditions on unearthed or impedance earthed systems,. Voltage factors, with the permissible duration of the maximum voltage, are given in Table 8.3.

VOLTAGE TRANSFORMERProtection of Voltage TransformersVoltage Transformers can be protected by H.R.C. fuses on the primary side for voltages up to 66kV. Fuses do not usually have a sufficient interrupting capacity for use with higher voltages.

In some cases protection on the primary is omitted. The secondary of a Voltage Transformer should always be protected by fuses or a miniature circuit breaker (MCB).

CURRENT TRANSFORMERCURRENT TRANSFORMERThe current transformers may be either of bushing type or wound type.CT should be selected with a rating 25% greater than the max current that is likely to flow during normal operation.Protective CT should have high saturation factor.The secondary circuit must not be interrupted while the primary winding is energized. The induced secondary e.m.f. under these circumstances will be high enough to present a danger to life and insulation.Protection class current transformers must retain a reasonable accuracy up to the largest relevant current. This value is known as the accuracy limit currentThe ratio of the accuracy limit current to the rated current is known as the 'accuracy limit factor

CURRENT TRANSFORMERThe accuracy class of protection current transformers is shown in TableClass PS Current TransformersThe classification of Table 5 is only used for overcurrent protection PS commonly used with unit protection schemes Knee point is a key factor in the PS class CT

POWER TRANSFORMERRATINGS :Transformer ratings shall be such that the transformer can deliver its rated current under steady loading conditions without exceeding the limits of temperature-rise specified in IS : 2026 ( Part II ) - 1977* assuming that the applied voltage is equal to the rated voltage and that the supply is at rated frequency.

SERVICE CONDITIONS :Transformers complying with IS-2026 are suitable for operation continuously at their ratings, provided the temperature of the cooling air or water does not exceed any of the reference ambient temperatures specified

POWER TRANSFORMERkVA Ratings:kVA ratings for three-phase transformers are given in below table

For single-phase transformers intended for use in three-phase banks, the kVA ratings are one-third of the values in Table 2.

POWER TRANSFORMEROperation at Other than Rated Voltage : - A transformer built in accordance with IS-2026 may be operated at its rated kVA at any voltage within +/- 10 percent of the rated voltage of that particular tap.- The transformer shall be capable of delivering rated current at a voltage equal to 105 percent of the rated voltage.Operation at Rated Frequency : The frequency for A transformer built in accordance with IS-2026 standard shall be 50 Hz with tolerance of +/- 3 percent.

Temp Rise: The transformer shall confirm to the requirements of temperature rise specified in IS : 2026 (Part II)

POWER TRANSFORMERInsulation Levels :The insulation levels shall be in accordance with IS : 2026 (Part III)- 19777.Terminal markings, tappings and Connections :The terminal markings, tapings and connections shall be inaccordance with IS : 2026 ( Part IV )-1977Requirement with regards to Ability to withstand S.C. Transformers shall be designed and constructed to withstandwithout damage the thermal and dynamic effects of external short circuit under the conditions specified in IS:2026.

POWER TRANSFORMERCRITERIA FOR SELECTION OF POWER TRANSFORMERS ( ABOVE 1600 kVA)Ratings : The secondary no-load voltage should be specified 5 percent more than the nominal voltage to compensate the transformer regulation partly. For transformers requiring to be operated in parallel, the voltage ratio should be selected in accordance with guidelines given in IS : 10028 ( Part 2 )-1981*.Taps : On-load tap changers on HV side should be specified, wherever required. The total number of taps should be 16 in steps of 1.25 percent.. Off-circuit taps, when specified, should be in the range of 2.5 percent and +/- 5 percent provided on the HV side.

POWER TRANSFORMERConnection Symbol :The preferred connections for two winding transformers up to 66 kV high voltage ( HV ) side rating are delta/star ( Dyn ) and star/star ( YNyn ). For higher voltages, connections star/star (YNyn) or star/delta ( YNd ) may be preferred. The selection of connection group should be made taking into consideration the requirements of parallel operation with other transformers Impedance : The transformer impedance is decided taking into Consideration the secondary fault levels and the voltage dip. typical impedance values are given IS : 2026 ( Part 1 )-19777.

POWER TRANSFORMERTermination Arrangement :

Primary and secondary terminals may be bare bushings, cable boxes or bus trunking depending upon the method of installation. It is preferable to specify disconnecting chamber between transformer terminals and cable box to facilitate disconnection of transformer.

OTHER DEVICES AND EQUIPMENTSDue to the time constraint following devices/equipments are not covered in detail !!!Circuit BreakersIsolator and earth SwitchLABattery and battery ChargerACDBDCDBAHU for Control roomControl & Relay Panel

SIEMENS

THANK YOU

For your Patience !

Technically single us arrangement, however offers flexibility of one CB maintenance without feeder shut down.It is the most economical system. Requires one Breaker per circuit on an average , however offers flexibility of two breakers per circuit.Disadvantage is that it needs complex protection schemePoses problems for future expansionThis is one method of reducing shut down of number of circuits in case of bus fault.Double bus offers flexibility to share load and busbar maintenance.This is a combination of Double bus system with a transfer bus.Offers flexibility of bus outageOffers flexibility to take one breaker outage at a time

As there are 3 breakers catering to 2 feeders , its called one and a half breaker arrangement.This scheme is expensiveHas maximum flexibility for Busbar outage as well as breaker outageA fault on any bus , doesnt affect continuity to supply