The document discusses various aspects of extra high voltage (EHV) transmission equipment, including switching schemes, line towers, conductors, switchyard types and layouts. It describes common switching schemes such as single bus, main and transfer, and double bus configurations. Key factors that influence switching scheme selection are also outlined. Additionally, the document provides details on transmission line components like towers, hardware, and conductor types. Specific equipment ratings and parameters are defined for 400kV, 220kV and 132kV systems. General guidelines for switchyard layout and design are also presented.

1. EHV Transmission Equipments

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Over view
 Switching Schemes.
 Line Towers.
 Type of conductors.
 Switchyard types.
 Switchyard equipments.
 Switchyard Layouts.

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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.
 Suspension Towers.

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Tower Design
 Wind Force.
 Conductor Tension.
 Span.
 Type of conductor.

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Tower Hardwares
 Insulator Strings.
 Vibration Dampers.
 Spacers.
 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 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) Rated one minute power
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 .
g. Corona extinction voltage Not less than 320 kV rms

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220kV Equipments
a. Rated voltage 245 kV
b. Rated frequency 50 Hz
c. Rated short time withstand
current capacity
40 kA rms for one (1) second
d. Insulation levels for 245kV Circuit
breakers and Disconnecting
Switches
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
a) +/- 1050 kVp between live
terminals and earth.
b) +/- 1050 kVp impulse on one
terminal and other terminal
earthed (across isolating
distance).
f. Max. Radio interference voltage
at 156kVrms
1000 micro volts for frequency
between 0.5 Mhz and 2.0 Mhz for all
equipment.

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132kV Equipments
a. Rated voltage 145 kV
b. Rated frequency 50 Hz
c. Rated short time withstand
current capacity
31.5 kA rms for one (1) second
d. Insulation levels for 145kV Circuit
breakers and Disconnecting
Switches
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
a) +/- 460 kVp between live
terminals and earth.
b) +/- 460 kVp impulse on one
terminal and other terminal
earthed (across isolating
distance).
f. Max. Radio interference voltage
at 92kVrms
1000 micro volts for frequency
between 0.5 Mhz and 2.0 Mhz for all
equipment.

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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
 Dead tank/Live tank type.
 Bar Primary type.
 Ring Type.
 No. of Cores.
 Ratio.
 Accuracy.

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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.
 Location.

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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.
 Coupling (Phase to Phase).

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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
maintenance purpose.

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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.
 Lighting to be provided by fixtures on LM platform.

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