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.

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.

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.

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).

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.

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.