Skip to main content

High voltage bus bar types

Short answer

Different types include single bus, sectionalised single, main and transfer, double bus, double bus double breaker, breaker-and-a-half, and ring bus. Main and transfer bus allows feeder breaker maintenance without outage using a bus coupler; advantages: low cost, simple layout. Disadvantages: main bus fault causes full outage, only one bypass at a time, complex switching.

Write down the different types of high voltage bus bar with appropriate line diagram. Write the advantages and disadvantages of main and transfer bus bar.

A busbar is a conductor in a switchyard to which incoming and outgoing circuits are connected. Its arrangement decides reliability, flexibility of maintenance and cost.

Types of HV busbar arrangement

1. Single bus: all circuits on one bus. Cheap, but any bus fault or maintenance shuts down everything.

   L1    L2    L3
   |     |     |
  [CB]  [CB]  [CB]
 ==+=====+=====+==  bus
  [CB]  [CB]
   |     |
   G1    T1

2. Sectionalised single bus: bus split by a bus-section breaker; a fault affects only one section.

3. Main and transfer bus: each circuit normally on the main bus; a bus coupler (transfer) breaker can take over any one feeder whose breaker is under maintenance.

 Main bus     ===+========+========+===
                 |        |        |
               [CB]     [CB]    [BC] coupler
                 |        |        |
 Transfer bus ---+--/ ----+--/ ----+---
                 |  bypass isolator
                 L1       L2

4. Double bus (double bus single breaker): two main buses; each circuit can be connected to either bus through isolators, with a bus coupler.

 Bus-1 ===+=========+=====+===
          |         |    [BC]
 Bus-2 ===+=========+=====+===
          | (isolators)
         [CB]      [CB]
          L1        L2

5. Double bus double breaker: each circuit has two breakers, one to each bus. Very reliable, costly.

6. Breaker-and-a-half (one-and-half breaker): three breakers for two circuits between two buses. Common at 220 kV and 400 kV.

7. Ring (mesh) bus: breakers form a closed loop; each circuit between two breakers.

Main and transfer bus: advantages

  • Any feeder breaker can be taken out for maintenance without interrupting that feeder (it is fed through the transfer bus and bus coupler).
  • Low cost compared with double bus or breaker-and-a-half: only one extra breaker.
  • Simple layout and protection.
  • Suitable for 33–132 kV substations.

Main and transfer bus: disadvantages

  • A fault on the main bus or its maintenance shuts down the whole substation (no second main bus).
  • Only one breaker at a time can be bypassed.
  • Protection of the transferred feeder must be switched to the bus coupler, so switching is more complex and error-prone.
  • More isolators and switching operations; needs interlocking.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Power Plant Design chapter 4 questions →