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Home / Download Center / Electrical Engineering Books and Technical Guides / Power substation guides / Substation single bus scheme with bus section circuit breakers and interlockings

The single bus scheme

This technical course explains in details power substations using the single bus scheme with bus section circuit breakers. You will be introduced to the use of protective grounding when performing maintenance work in an power substation.

Substation single bus scheme with bus section circuit breakers and interlockings
Substation single bus scheme with bus section circuit breakers and interlockings

You will know why interlocking is required between circuit breakers and disconnecting switches in electric power substations. You will also know why interlocking of incoming line circuit breakers is required in electric power substations.

Figure 1 shows a single-line diagram of an electric power substation using the single bus scheme.

The single bus scheme is the most simple and economical way of arranging buses and switchgear in an electric power substation.

With this scheme, all power lines reaching the substation are connected to the same bus, with each line being permanently connected to the bus through a circuit breaker and two disconnecting switches connected in series.

Opening the two disconnecting switches in a line isolates the corresponding circuit breaker from the rest of the substation. This allows maintenance of the circuit breaker without affecting the rest of the substation.

Single-line diagram of an electric power substation implemented using the single bus scheme
Figure 1 – Single-line diagram of an electric power substation implemented using the single bus scheme

The single bus scheme with bus section circuit breakers

The single bus scheme has an obvious weakness: any fault on the bus results in an outage of the entire electric power substation, i.e., power can no longer be routed to loads via the substation until the bus is repaired.

To alleviate this drawback, it is common to provide the bus in a substation implemented using the single bus scheme with one or several bus section circuit breaker(s).

Figure 2 shows the single-line diagram of an electric power substation in which the single bus can be separated into two sections using a bus section circuit breaker. The bus section circuit breaker is generally closed during normal operation.

When a fault occurs on the bus, the bus section circuit breaker is opened to separate the bus into two sections. This allows the faulty bus section to be isolated, thereby limiting the number of loads that lose power.

Ideally, the loads and AC power sources must be distributed evenly on the bus sections to ensure that the number of loads that lose power following a fault on a particular section of the bus is limited to minimum.

Single-line diagram of an electric power substation implemented using the single bus scheme with bus section circuit breakers
Figure 2 – Single-line diagram of an electric power substation implemented using the single bus scheme with bus section circuit breakers

Reliability of such substations

This section of the discussion deals with the reliability of an electric power substation using the single bus scheme with bus section circuit breakers. The section starts with a series of subsections, each one describing how a fault at a particular location in the electric power substation affects the supply of power to loads.

The section then concludes on the reliability of electric power substations using the single bus scheme with bus section circuit breakers.

Title:Substation single bus scheme with bus section circuit breakers and interlockings – Festo Didactic
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Substation single bus scheme with bus section circuit breakers and interlockings
Substation single bus scheme with bus section circuit breakers and interlockings

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2 Comments


  1. Raman
    Jan 31, 2019

    Why on the MV switchgear are disconnectors if we can rack out drawers with cirquit breaker? I saw this on the switcgear where the CB doesn’t possible rack out. For a coupler cb the meaning is clear.


    • Gary Leung
      Mar 04, 2020

      Let me try to answer the question.
      Not all MV switchgear can be rack-out type, such as, gas switches.

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