switchyard

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EHV Transmission

Equipments

C. K. Thakur C. K. Thakur

Chief Design Engineer

(Project Engineering Electrical)

NTPC

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Over view



 Switching Schemes.Switching Schemes.



 Type of Towers.Type of Towers.



 Type of conductors.Type of conductors.



 Switchyard types.Switchyard types.



 Switchyard equipments.Switchyard equipments.



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Switching schemes

 Single bus.

 Main and Transfer (sectionalised).  Double bus.

 One and half breaker scheme.  Double main and Transfer

(Sectionalised).

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Factors Affecting Switching

Scheme

 System Security/Reliability. - Feeder Fault. - Bus Fault. - Equipment Failure. - Redundancy.

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Factors Affecting Switching

Scheme (Contd.)

 Operational Flexibility.  Ease of Maintenance.  Simplicity of Protection Arrangements.  Ease of Extension.  Area available.  Cost.

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Line Towers

 Single Circuit.  Double Circuit.  Dead end type.  Tension Towers.

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Tower Design

 Wind Force.

 Conductor Tension.  Span.

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Tower Hardwares

 Insulator Strings.  Vibration Dampers.  Spacers.

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Type of Conductor

 ACSR Moose (800A).  Zebra (700A).

 Rabbit (190A).  Dog (290A).

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Switchyard Type

 Conventional Air Insulated Type.  Gas Insulated type.

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Switchyard Equipments.

 Circuit Breaker.  Disconnectors.

 Current Transformers.

 Capacitor Voltage Transformers.  Lightning Arrestors.

 Post Insulators.  Wave Traps

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General Parameters

 Dielectric Parameters .(IEC 694)

- Power Frequency Voltage. - Lightning Impulse Voltage. - Switching Impulse Voltage. - Corona Extinction Voltage. - RIV Level.

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400kV Equipments

a. Rated voltage 420 kV b. Rated frequency 50 Hz c. Rated short time withstand

current capacity

40 kA rms for one (1) second d. Insulation levels for 420kV Circuit

breakers and Disconnecting Switches

e . i ) R at ed o ne m in ut e p ow er Frequency withstand voltage

a) 520 kV rms between live terminals and earth. b) 610 kV rms across isolating

distance. ii) Rated lightning impulse

withstand voltage

a) +/- 1425 kVp between live terminals and earth.

b) +/- 1425 kVp impulse on one terminal and 240 kVp power frequency of opposite polarity on other terminal (across isolating distance).

iii) Rated switching impulse withstand voltage

a) +/- 1050 kVp between live terminals and earth. b) +/- 900 kVp impulse on one

terminal and 345 kVp power frequency of opposite polarity on other terminal (across isolating distance).

f. Max. Radio interference voltage at 266kVrms

1000 micro volts for frequency between 0.5 Mhz and 2.0 Mhz for all equipment. However, for insulator strings the measurement would be at 305 kV

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220kV Equipments

current capacity

40 kA rms for one (1) second d. Insulation levels for 245kV Circuit

e. i) Rated one minute power Frequency withstand voltage

a) 460 kV rms between live terminals and earth.

b) 460 kV rms across isolating distance.

ii) Rated lightning impulse withstand voltage

b) +/- 1050 kVp impulse on one terminal and other terminal earthed (across isolating distance).

1000 micro volts for frequency between 0.5 Mhz and 2.0 Mhz for all equipment.

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132kV Equipments

current capacity

31.5 kA rms for one (1) second d. Insulation levels for 145kV Circuit

e. i) Rated one minute power Frequency withstand voltage

a) 275 kV rms between live terminals and earth.

b) 275 kV rms across isolating distance.

ii) Rated lightning impulse withstand voltage

b) +/- 460 kVp impulse on one terminal and other terminal earthed (across isolating distance).

1000 micro volts for frequency between 0.5 Mhz and 2.0 Mhz for all

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General Parameters (Contd.)

 Rated Current.

 Short Time Current.  Creepage Distance.

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Circuit Breakers Type

 MOCB.  ABCB.  SF6

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Circuit Breaker

 Fault clearing.

 Load Make Break.  Break Time.

 Single/Multi Break.

 Voltage Distribution across breaks.  Closing resistors.

 Operating mechanism

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Disconnectors

 HCB Type.

 Double Break Type.  Pantograph type.

 Vertical Break type.

 Provision of Earth Switches.  Motor / Pneumatic operated.

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Current Transformer

 Bar Primary type.

 Dead tank/Live tank type.  Ring Type.

 No. of Cores.  Ratio.

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Capacitor Voltage Transformer

 Capacitance.  Voltage Ratio.  No. Of Cores.  Accuracy.

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Lightning Arrestor

 Gap Type / Gapless Type.  Voltage Rating.

 Energy Capability.  Monitoring.

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Post Insulators

 Voltage Rating.

 Cantilever Strength.  Fixing Details.

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Wave Trap

 Rated Inductance(0.5/1.0 mH).  Rated current.

 Band Width.

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Switchyard Layout Guidelines

 Place All Equpt. At ground level for

ease of maintenance.

 Busbars placed at right angles to

feeders.

 Accessibility of feeders from either

side of switchyard.

 Conductor crossings at right angles

be separated to achieve adequate clearances.

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Switchyard Layout

Guidelines(Contd.)

 For 400kV - Phase to Phase 4000 mm - Phase to earth 3500mm  For 220kV - Phase to Phase 2100 mm - Phase to earth 2100mm

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Switchyard Layout

Guidelines(Contd.)

 Lower level connections can be of

Rigid pipe or flexible conductor.

 Upper level connections can be of

strung type only.

 For aesthetic looks and similarity all

same equipments be in one line as far as possible.

 Road near circuit breaker be kept for

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Switchyard Layout

Guidelines(Contd.)

 Provide Double insulator strings for

upper level for safety reasons and to avoid busfaults due to conductor

snapping.

 Cable trenches to be routed for ease in

maintenance and movement.

 Lightning protection to be provided

using Lightning masts and/or shield wires.

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