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“Design of 400/220kV

Sub-station”

Sanjay Chatterjee

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Includes



Overview of 400kV sub-station



Design Process



Design considerations

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Imp.

considerations

in substation design



Safety of personnel and equipment



Reliability and Security



Adherence to



Statutory obligations

– I.E. rules, Environmental aspects



Electrical design considerations



Structural design considerations



Ease of maintenance

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System parameters

1000 mV (156kV) 1000 mV

(320kV) Radio interference voltage at 1MHZ (for

phase to earth voltage) 10.

40kA 40kA

Rated short ckt. Current for 1 sec. 8.

25mm/kV 25mm/kV

Min. creepage distance 7.

156kV 320kV

Corona Extinction voltage 6.

Effectively earthed System neutral earthing

5. 3 3 Number of phases 4. 50Hz 50Hz Rated frequency 3. 245kV 420kV

Max. operating voltage 2.

220kV 400kV

Nominal system voltage 1.

220kV 400kV

Description Sr.

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System parameters Contd..

Remarks 220kV 400kV Description Sr. (Line-ground) (open terminals) 460kV 460kV 530kV 460kV 680kV 520kV 610kV 630kV iii) One min. power freq.

withstand voltage (dry/wet) -- for lines

-- for CB / Isolator

-- for other equipments

1050kVp ii) Switching impulse

withstand voltage (dry/wet)

1050kVp 950kVp 1050kVp 1550kVp 1300kVp 1425kVp Rated insulation levels

i) Full wave impulse withstand voltage

-- for lines

-- for reactor/ X’mer -- for other equipments 11.

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Functions of substation equipments

To discharge lightning over voltages and switching over voltages to earth

7. Lightning Arrester

To step-down voltages for measurement, control & protection

6. Voltage Transformer

To step-down currents for measurement, control & protection

5. Current Transformer

To discharge the voltage on dead lines to earth 4. Earthing switch

Disconnection under no-load condition for safety, isolation and maintenance.

3. Isolators

Automatic switching during normal or abnormal conditions

2. Circuit Breaker

Incoming & outgoing ckts. Connected to bus-bar 1. Bus-Bar

Function Equipment

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Functions of substation equipments Contd…

Compensation of long lines. 14. Series Capacitor

To step-up or step-down the voltage and transfer power from one a.c. voltage another a.c. voltage at the same frequency.

13. Power Transformer

To provide compensations to reactive loads of lagging power factors

12. Shunt capacitors

To prevent high frequency signals from entering other zones.

11. Line –Trap

To provide connection between high voltage line & PLCC equipment

10. Coupling capacitor

To limit earth fault current 9. Neutral-Grounding

resistor

To control over voltages by providing reactive power compensation

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Functions of Associated system in substation

3. Illumination system (lighting) -- for switchyard

-- buildings -- roads etc.

To protect the outdoor substation equipment from lightning strokes. 2. Overhead earth wire shielding

or Lightning masts.

To provide an earthmat for connecting neural points, equipment body, support structures to earth. For safety of personnel and for enabling earth fault protection. To provide the path for discharging the earth currents from neutrals, faults, Surge

Arresters, overheads shielding wires etc. with safe step-potential and touch

potential. 1. Substation Earthing system

-- Earthmat

-- Earthing spikes -- Earthing risers

Function System

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Contd..

To provide alarm or automatic tripping of faulty part from healthy part and also to minimize damage to faulty equipment and associated system.

4. Protection system

-- protection relay panels -- control cables

-- circuit breakers -- CTs, VTs etc.

For Protective circuits, control circuits, metering circuits, communication circuits 5. Control cable

For communication, telemetry, tele-control, power line carrier protection etc.

7. PLCC system power line carries communication system

-- line trap

-- coupling capacitor -- PLCC panels

To provide supply path to various auxiliary equipment and machines.

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Contd…

To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to affected region to pin-point location of fire by indication in control room.

8. Fire Fighting system

-- Sensors, detection system -- water spray system

-- fire prot. panels, alarm system -- watertank and spray system

For internal and external communication

10. Telephone, telex, microwave, OPF

For supplying starting power, standby power for auxiliaries

9. Auxiliary standby power system -- diesel generator sets

-- switchgear

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Basic drawings for design/construction



Single Line Diagram



General Arrangement Drawing



Electrical Plan and Section

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Supporting drawings



Structural layout



Earthmat layout



Civil layout



Erection Key Diagram

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Earthmat Layout

@ @ @ @ @ @ @ @ @

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Erection Key Diagram

E W 2 E W 2 4 S 1 4 S 1 4 D T T M -2 E W 1 4 I 4 S 1 4 LA 4 P4 S 14 V 4 W 4 W 4 S 1 4 S 1 4 I 4 S 1 4 L A 4 S 1 R 1 4 S S T M -D 4 T 1 4 T 1 4 T 1 4 S 1 4 S 1 4 S 1 E W 2 E W 2 4 S 1 4 S 1 4 S 1 4 D T T M -1 4 S 2 4 S 2 4 S 2 E W 1 4 S S T M -D 4 T B SM 4 T B SM 4 T B SM 4 P 1 4 I 4 P 3 4 S 1 4 S 1 4 P 1 4 I 4 I C1 4 S 1 4 S 1 4 S 1 4 B 4 I 2 4 I 1 4 I 4 I C2 4 S 1 4 C2 4 C1 4 I 1 4 B E W 2 E W 2 4 S S T M -T 4 S 2 4 T M 4 S 2 4 S 1 4 S 1 4 S 1 4 D T T M -1 4 D T T M -2 E W 1 4 S 2 4 S 2 4 S 2 4 I 2 4 S 1 4 I C2 4 D T T M -1 4 D T T M -1 4 D T T M -1 4 D T T M -1 4 D T T M -1 4 D T T M -1 4 S S T M -D 4 L A 4 P 4 P 4 P 4 L A 4 L A 4 W 4 V 4 V 4 V 4W 4 S S T M -D 4 D T T M -1 4 D T T M -1 4 D T T M -1 4 S S T M -D 4 I 4 I 4 I 4 I 4 I 4I 4 W 4 P 4V 4 L A 4 P 4 L A 4 V 4 P 4 L A 4 V 4W 4 S S T M -D 4 D T T M -1 4 D T T M -1 4 S S T M -D 4 I 4 I 4 I 4 I 4 D T T M -1 4 I 4 S S T M -D 4 I 4 P 3 R 1 R 1 R 1 4LA 4 L A 4 L A 4 D T T M -2 4 P 3 4 P 3 4 I 4 I 4 I 4 D T T M -2 4 I 4 I 4 D T T M -2 4 I R 1 R 1 R 1 4 L A 4 L A 4 L A 4 P 3 4 P 3 4 I 4 I 4 D T T M -2 4 D T T M -2 4 I 4 I 4 P 3 4 I 4 D T T M -2 4 I 4 B 4 B 4 B 4 D T Q B -2 4 D T Q B -2 4 D T Q B -2 4 I2 4I1 4 I 4 P 1 4 IC 2 4 P 1 4 IC 1 4I2 4I1 4 I1 4 B 4 B 4 B 4 C 2 4 C 1 4 I1 4I2 4 C 2 4 C 1 4 I1 4I2 4 C 2 4 C 1 4 I1 4I2 4 B 4 B 4 B 4 P 1 4 I2 4I1 4 IC 2 4 P 1 4 IC 1 4 I2 4I1 4 I 4 D T Q B -1 4 D T Q B -1 4 D T Q B -1 4 I1 4 C 2 4 C 1 4 I1 4 B 4I2 4 B 4C1 4C2 4I1 4I2 4 B 4C1 4C2 4I1 4I2 4 W 1 4 W 1 4 W 1 4 W 1 4 W 1 4 W 1 4 W 1 4 W 1 4 W 1 4 W 1 N 1 R2 R2 N 1

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Lighting Design

 Adequate lighting is necessary for safety of working personnel and O&M

activities

 Recommended value of Illumination level

 Control & Relay panel area - 350 Lux (at floor level)  Test laboratory - 300 Lux

 Battery room - 100 Lux  Other indoor area - 150 Lux

 Switchyard - 50 Lux (main equipment)

- 20 Lux (balance Area / road @ ground level)

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Single Bus System

4. Can be used only where loads can be interrupted or have other supply

arrangements.

3. Sectionalizing increases flexibility 3. Bus cannot be extended

without completely de-energizing substations 3. Simple Protection

2. Not used for large substations.

2. Difficult to do any maintenance

2. Simple to Operate

1. Used for distribution substations upto 33kV 1. Fault of bus or any circuit

breaker results in shut-down of entire substation

1. Low cost

Remarks Demerits

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Main & transfer busbar system

3. Fault of bus or any circuit breaker results in shutdown of entire

substation. 3. Potential devices may

be used on the main bus

. 2. Switching is somewhat complex when

maintaining a breaker 2. Any breaker can be

taken out of service for maintenance.

1. Used for 110kV

substations where cost of duplicate bus bar system is not justified

1. Requires one extra breaker coupler

1. Low initial & ultimate cost

Remarks Demerits

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Double Bus Bar Single Breaker system

5. Bus couplers failure takes entire substation out of service. 4. Line breaker failure takes all circuits connected to the bus out of service.

3. High exposure to bus fault. 2. Bus protection scheme may cause loss of substation when it operates.

2. Half of the feeders connected to each bus

1. Most widely used for 66kV, 132kv, 220kV and

important 11kv, 6.6kV, 3.3kV substations. 1. Extra bus-coupler circuit

breaker necessary. 1. High flexibility

Remarks Demerits

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Double Bus Bar Double Breaker system

4. High reliability

3. Any breaker can be taken out of service for maintenance.

2. Used only for very important, high power, EHV substations.

2. Would lose half of the circuits for breaker fault if circuits are not connected to both the buses.

2. Has flexibility in

permitting feeder circuits to be connected to any bus

1. Not used for usual EHV substations due to high cost.

1. Most expensive 1. Each has two

associated breakers

Remarks Demerits

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Double main bus & transfer bus system

7. Bus fault does not remove any feeder from the service

6. Either main bus can be taken out of service at any time for

maintenance.

5. Simple operation, no isolator switching required

4. All switching done with breakers 3. Breaker failure on bus side breaker removes only one ckt. From service 2. Highly reliable

1. Preferred by some utilities for 400kV and

220kV important substations.

1. High cost due to three buses

1. Most flexible in operation

Remarks Demerits

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One & half breaker scheme

6. Selective tripping

5. All switching by breaker. 4. Each circuit fed by two breakers.

3. Requires 1 1/2 breaker per feeder.

2. Preferred. 2. Protection and

auto-reclosing more complex since middle breaker must be

responsive to both associated circuits. 2. Any breaker can be removed

from maintenance without interruption of load.

1. Used for 400kV & 220kV

substations. 1. One and half

breakers per circuit, hence higher cost 1. Flexible operation for breaker

maintenance

Remarks Demerits

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Mesh (Ring) busbar system

4. Breaker failure during fault on one circuit causes loss of additional circuit because of breaker failure.

3. Requires VT’s on all circuits

because there is no definite voltage reference point.

These VT’s may be required in all cases for synchronizing live line or voltage indication

2.Auto-reclosing and protection complex.

1. Most widely used for very large power stations having large no. of incoming and outgoing lines and high power transfer.

1. If fault occurs during bus

maintenance, ring gets separated into two sections. 1. Busbars gave some operational flexibility Remarks Demerits Merits

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Minimum Clearances

4300 mm 6400 mm 3. Sectional clearance 2100 mm 4200 mm (Rod-conductor configuration) 4000 mm (Conductor-conductor configuration) 2. Phase to phase 2100 mm 3500 mm 1. Phase to Earth 220kV 400kV

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Bus Bar Design

 Continuous current rating. Ampacity caculation as per IEEE:738

 Short time current rating (40kA for 1 Sec.) IEC-865

 Stresses in Tubular Busbar

 Natural frequency of Tubular Busbar

 Deflection of Tube

 Cantilever strength of Post Insulator

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Gantry Structure Design

Clearances No wind Max. (ACSR 750C/ AAAC 850C) 5. T <= 70% of UTS 100% Every Day 4. T <= 22% of UTS No wind Every Day 3. 36% Min. 2. No wind Min. 1. Limits Wind Pressure Temp Sr.

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Contd..

 Short Circuit Forces calculation

As per IEC : 865

Short circuit forces during short circuit Short circuit forces after short circuit

Short circuit forces due to “Pinch” effect for Bundled conductor Spacer span calculation

 Factor of safety of 2.0 under normal condition and 1.5 under short circuit

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Spacer span Vs Short Ckt. forces

GRAPH OF SPACER SPAN Vs CONDUCTOR TENSION FOR 400 KV TWIN MOOSE ACSR CONDUCTOR

0.00 2000.00 4000.00 6000.00 8000.00 10000.00 12000.00 0 2 4 6 8 10 12 14 SPACER SPAN IN MTRS. C O N D U C T O R T E N S IO N P E R P H A S E I N K G .

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Earthing Design



Guiding standards – IEEE 80, IS:3043, CBIP-223.



400kV & 220kV system are designed for 40kA.



Basic Objectives:



Step potential within tolerable



Touch Potential limit



Ground Resistance



Adequacy of Ground conductor for fault current (considering

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Lightning Protection – Ground Wire

FIG-4b FIG-4a

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References

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