EHV Transmission Equipments

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EHV Transmission Equipments

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

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Over view

• Switching Schemes.
• Type of 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).
• 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.

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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
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220kV Equipments
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132kV Equipments
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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.

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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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