switchyard

EHV Transmission Equipments

C. K. Thakur Chief Design Engineer (Project Engineering Electrical) NTPC

Over view

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Switching Schemes.

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Type of Towers.

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Type of conductors.

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Switchyard types.

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Switchyard equipments.

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Switchyard Layouts.

Switching schemes

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Single bus. Main and Transfer (sectionalised). Double bus. One and half breaker scheme. Double main and Transfer  (Sectionalised). Double Breaker 

Factors Affecting Switching Scheme 

System Security/Reliability.

- Feeder Fault. - Bus Fault. - Equipment Failure. - Redundancy.

Factors Affecting Switching Scheme (Contd.) 

Operational Flexibility.

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Ease of Maintenance.

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Simplicity of Protection  Arrangements. Ease of Extension.  Area available. Cost.

Line Towers

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Single Circuit.

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Double Circuit.

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Dead end type.

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Tension Towers.

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Suspension Towers.

Tower Design

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Wind Force.

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Conductor Tension.

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Span.

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Type of conductor.

Tower Hardwares

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Insulator Strings.

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Vibration Dampers.

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Spacers.

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Earthwire & OPGW.

Type of Conductor

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 ACSR Moose (800A).

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Zebra (700A).

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Rabbit (190A).

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Dog (290A).

Switchyard Type

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Conventional Air Insulated Type.

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Gas Insulated type.

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 Air Insulated (Enclosed type).

Switchyard Equipments.

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Circuit Breaker.

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Disconnectors.

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Current Transformers.

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Capacitor Voltage Transformers.

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Lightning Arrestors.

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Post Insulators.

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Wave Traps

General Parameters

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Dielectric Parameters .(IEC 694)

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

400kV Equipments a. b. c. d.

e.

Rated voltage 420 kV Rated frequency 50 Hz Rated short time withstand 40 kA rms for one (1) second current capacity Insulation levels for 420kV Circuit breakers and Disconnecting Switches i ) R at ed o ne m in ut e p ow er   a) 520 kV rms between live Frequency withstand voltage terminals and earth. b)

ii) Rated lightning impulse withstand voltage

iii) Rated switching impulse withstand voltage

f.

Max. Radio interference voltage at 266kVrms

g.

Corona extinction voltage

610 kV rms across isolating distance. 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). 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). 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 Not less t han 320 kV rms .

220kV Equipments a. b. c. d.

e.

Rated voltage 245 kV Rated frequency 50 Hz Rated short time withstand 40 kA rms for one (1) second current capacity Insulation levels for 245kV Circuit breakers and Disconnecting Switches i) Rated one minute power  a) 460 kV rms between live Frequency withstand voltage terminals and earth. b) ii) Rated lightning impulse withstand voltage

f.

Max. Radio interference voltage at 156kVrms

460 kV rms across isolating distance. a) +/- 1050 kVp between live terminals and earth. 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.

132kV Equipments a. b. c. d.

e.

Rated voltage 145 kV Rated frequency 50 Hz Rated short time withstand 31.5 kA rms for one (1) second current capacity Insulation levels for 145kV Circuit breakers and Disconnecting Switches i) Rated one minute power  a) 275 kV rms between live Frequency withstand voltage terminals and earth. b) ii) Rated lightning impulse withstand voltage

f.

Max. Radio interference voltage at 92kVrms

275 kV rms across isolating distance. a) +/- 460 kVp between live terminals and earth. 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 equipment.

General Parameters (Contd.)

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Rated Current.

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Short Time Current.

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Creepage Distance.

Circuit Breakers Type

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MOCB.  ABCB. SF6

Circuit Breaker

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Fault clearing.

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Load Make Break.

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Break Time.

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Single/Multi Break.

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Voltage Distribution across breaks.

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Closing resistors.

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Operating mechanism (Spring/Pneumatic/Hydraulic)

Disconnectors

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HCB Type.

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Double Break Type.

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Pantograph type.

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Vertical Break type.

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Provision of Earth Switches.

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Motor / Pneumatic operated.

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Gang operated/Single pole type.

Current Transformer

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Bar Primary type.

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Dead tank/Live tank type.

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Ring Type.

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No. of Cores.

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Ratio.

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 Accuracy.

Capacitor Voltage Transformer

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Capacitance.

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Voltage Ratio.

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No. Of Cores.

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 Accuracy.

Lightning Arrestor

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Gap Type / Gapless Type.

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Voltage Rating.

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Energy Capability.

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Monitoring.

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Location.

Post Insulators

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Voltage Rating.

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Cantilever Strength.

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Fixing Details.

Wave Trap

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Rated Inductance(0.5/1.0 mH).

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Rated current.

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Band Width.

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Coupling (Phase to Phase).

Switchyard Layout Guidelines

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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.

Switchyard Layout Guidelines(Contd.) 

For 400kV - Phase to Phase 4000 mm - Phase to earth 3500mm

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For 220kV - Phase to Phase 2100 mm - Phase to earth 2100mm

Switchyard Layout Guidelines(Contd.) 

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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 maintenance purpose.

Switchyard Layout Guidelines(Contd.) 

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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. Lighting to be provided by fixtures on