1. EHV Transmission Equipments
C. K. Thakur
Chief Design Engineer
(Project Engineering Electrical)
NTPC

2. Over view Switching Schemes. Type of Towers. Type of conductors.
Switchyard types.
Switchyard equipments.
Switchyard Layouts.
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3. 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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4. Factors Affecting Switching Scheme
System Security/Reliability.
- Feeder Fault.
- Bus Fault.
- Equipment Failure.
- Redundancy.
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5. Factors Affecting Switching Scheme (Contd.)
Operational Flexibility.
Ease of Maintenance.
Simplicity of Protection Arrangements.
Ease of Extension.
Area available.
Cost.
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6. Line Towers Single Circuit. Double Circuit. Dead end type.
Tension Towers.
Suspension Towers.
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7. Tower Design Wind Force. Conductor Tension. Span. Type of conductor.
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8. Tower Hardwares Insulator Strings. Vibration Dampers. Spacers.
Earthwire & OPGW.
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9. Type of Conductor ACSR Moose (800A). Zebra (700A). Rabbit (190A).
Dog (290A).
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10. Switchyard Type Conventional Air Insulated Type. Gas Insulated type.
Air Insulated (Enclosed type).
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11. Switchyard Equipments.
Circuit Breaker.
Disconnectors.
Current Transformers.
Capacitor Voltage Transformers.
Lightning Arrestors.
Post Insulators.
Wave Traps
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12. General Parameters Dielectric Parameters .(IEC 694)
- Power Frequency Voltage.
- Lightning Impulse Voltage.
- Switching Impulse Voltage.
- Corona Extinction Voltage.
- RIV Level.
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13. 400kV Equipments
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14. 220kV Equipments
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15. 132kV Equipments
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16. General Parameters (Contd.)
Rated Current.
Short Time Current.
Creepage Distance.
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17. Circuit Breakers Type
MOCB.
ABCB.
SF6
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18. 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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19. 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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20. Current Transformer Bar Primary type. Dead tank/Live tank type.
Ring Type.
No. of Cores.
Ratio.
Accuracy.
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21. Capacitor Voltage Transformer
Capacitance.
Voltage Ratio.
No. Of Cores.
Accuracy.
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22. Lightning Arrestor Gap Type / Gapless Type. Voltage Rating.
Energy Capability.
Monitoring.
Location.
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23. Post Insulators Voltage Rating. Cantilever Strength. Fixing Details.
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24. Wave Trap Rated Inductance(0.5/1.0 mH). Rated current. Band Width.*
07/16/96
Wave Trap
Rated Inductance(0.5/1.0 mH).
Rated current.
Band Width.
Coupling (Phase to Phase).
1 December 2018 *

25. 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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26. 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 mm
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27. 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.
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28. 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.
1 December 2018