EHV Transmission Equipments
C. K. Thakur
Chief Design Engineer
(Project Engineering Electrical)
NTPC
April 8, 2023 22
Over view
Switching Schemes. Type of Towers. Type of conductors. Switchyard types. Switchyard equipments. Switchyard Layouts.
April 8, 2023 33
Switching schemes
Single bus. Main and Transfer (sectionalised). Double bus. One and half breaker scheme. Double main and Transfer (
Sectionalised). Double Breaker
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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.
April 8, 2023 66
Line Towers
Single Circuit. Double Circuit. Dead end type. Tension Towers. Suspension Towers.
April 8, 2023 77
Tower Design
Wind Force.Wind Force. Conductor Tension.Conductor Tension. Span.Span. Type of conductor.Type of conductor.
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Tower Hardwares
Insulator Strings.Insulator Strings. Vibration Dampers.Vibration Dampers. Spacers.Spacers. Earthwire & OPGW.Earthwire & OPGW.
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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. Air Insulated (Enclosed 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 kVb. Rated frequency 50 Hzc. Rated short time withstand
current capacity40 kA rms for one (1) second
d. Insulation levels for 420kV Circuitbreakers and DisconnectingSwitches
e. i) Rated one minute powerFrequency withstand voltage
a) 520 kV rms between liveterminals and earth.
b) 610 kV rms across isolatingdistance.
ii) Rated lightning impulsewithstand voltage
a) +/- 1425 kVp between live terminalsand earth.
b) +/- 1425 kVp impulse on oneterminal and 240 kVp powerfrequency of opposite polarity onother terminal (across isolatingdistance).
iii) Rated switching impulsewithstand voltage
a) +/- 1050 kVp between liveterminals and earth.
b) +/- 900 kVp impulse on oneterminal and 345 kVp powerfrequency of opposite polarity onother terminal (across isolatingdistance).
f. Max. Radio interference voltageat 266kVrms
1000 micro volts for frequencybetween 0.5 Mhz and 2.0 Mhz for allequipment. However, for insulatorstrings the measurement would beat 305 kV .
g. Corona extinction voltage Not less than 320 kV rms
April 8, 2023 1144
220kV Equipments
a. Rated voltage 245 kVb. Rated frequency 50 Hzc. Rated short time withstand
current capacity40 kA rms for one (1) second
d. Insulation levels for 245kV Circuitbreakers and DisconnectingSwitches
e. i) Rated one minute powerFrequency withstand voltage
a) 460 kV rms between liveterminals and earth.
b) 460 kV rms across isolatingdistance.
ii) Rated lightning impulsewithstand voltage
a) +/- 1050 kVp between liveterminals and earth.
b) +/- 1050 kVp impulse on oneterminal and other terminalearthed (across isolatingdistance).
f. Max. Radio interference voltageat 156kVrms
1000 micro volts for frequencybetween 0.5 Mhz and 2.0 Mhz for allequipment.
April 8, 2023 1155
132kV Equipments
a. Rated voltage 145 kVb. Rated frequency 50 Hzc. Rated short time withstand
current capacity31.5 kA rms for one (1) second
d. Insulation levels for 145kV Circuitbreakers and DisconnectingSwitches
e. i) Rated one minute powerFrequency withstand voltage
a) 275 kV rms between liveterminals and earth.
b) 275 kV rms across isolatingdistance.
ii) Rated lightning impulsewithstand voltage
a) +/- 460 kVp between liveterminals and earth.
b) +/- 460 kVp impulse on oneterminal and other terminalearthed (across isolatingdistance).
f. Max. Radio interference voltageat 92kVrms
1000 micro volts for frequencybetween 0.5 Mhz and 2.0 Mhz for allequipment.
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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
(Spring/Pneumatic/Hydraulic)
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Disconnectors
HCB Type. Double Break Type. Pantograph type. Vertical Break type. Provision of Earth Switches. Motor / Pneumatic operated. Gang operated/Single pole type.
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Current Transformer
Bar Primary type. Dead tank/Live tank type. Ring Type. No. of Cores. Ratio. Accuracy.
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Capacitor Voltage Transformer
Capacitance. Voltage Ratio. No. Of Cores. Accuracy.
April 8, 2023 2222
Lightning Arrestor
Gap Type / Gapless Type. Voltage Rating. Energy Capability. Monitoring. Location.
April 8, 2023 2233
Post Insulators
Voltage Rating. Cantilever Strength. Fixing Details.
April 8, 2023 2244
Wave Trap
Rated Inductance(0.5/1.0 mH). Rated current. Band Width. Coupling (Phase to Phase).
April 8, 2023 2255
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 maintenance purpose.
April 8, 2023 2288
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.
Lighting to be provided by fixtures on LM platform.