Power System Configurations.


Switchyards Design Considerations

Fault level 

  • Expressed as MVA or kA and duration of 1-3 sec. 
  • Depends upon source impedance ie distances from the power sources 
  • All CBs to be rated for Fault level 
  • Earthing switches for making the fault level 
  • All busbars, bus supports to be designed to withstand mechanical forces due to short circuits. 

Safety Clearance & Creepage Distance

  • As per voltage level among live parts & earth 
  • Shortest path taken on surface by leakage current. 

Grounding & Lightning Protection

  • Grid/Mesh is formed and burried in ground 
  • Earthing Electrodes (pipe/rod/plates) are connected to mesh 
  • Shield wires to protect against direct lightning strokes 

Safety Interlocks in Control schemes

  • Isolator Open/Close possible only if CB is open. 
  • E/S closing possible only when isolator is closed.etc.

Double Main & Transfer Bus Arrangement (DMT)

Almost all PGCIL 220kV substations use this arrangement

  • 245kV Switchyard Layout

Almost all PGCIL 220kV substations use this arrangement

  • One and a Half Breaker Arrangement
Almost all PGCIL 765kv,400kV substations use this arrangemen
  • Three Main & Transfer Bus Arrangement
Practiced in Europe, Germany
  • Ring or Mesh System
  • Power Line Carrier Coupling

Switchyards Design features

Design Aspects 

  • Single line diagram 
  • Busbar Arrangement 
  • Fault level 
  • Type of construction 
  • Creepage & Clearance 
  • Grounding & Lightning Protection 
  • Safety Interlocks 
  • Other Miscellaneous items e.g lighting , civil

Considerations for Choice of Busbar Arrangement

  • Importance of Substation 
  • Reliability 
  • Redundancy 
  • Economics and availability of finance 
  • Availability of Space and Right Of Way for approaching lines 
  • Future Expansion

Switching Devices 

 Circuit Breaker
Current Carrying
  Current Making
Current Breaking 
  • Isolator is rated only for carrying current, 
  • Make/Break small line charging current.
  • OPEN/CLOSE operation done under ZERO current condition.

Power System Configurations

Power System Structure

  • Transmission circuits handle/route largest power , interconnect various power stations & feed to load centres 
  • Subtransmission circuits feed to distribution substations & bulk consumers within a geographical area. 
  • Distribution circuits fed from distribution substations feed domestic , medium size industries and commercial consumers.

Requirement for planning of the T&D Network configuration.

  • Voltage levels , Amount of Power Transfer, Length of transmission lines, Fault level 
  • Importance of the consumers / customers 
  • Clearance times, Stability