Bays and their equipment

A bay is the set of equipment that connects one circuit to the buses of a high-voltage (HV) switchyard: a line, a transformer, the bus coupler or the bus section. Each kind of bay carries its own devices in a fixed order on the single-line diagram (SLD), and the yard lays the bays out side by side.

Read first: Single-line diagram (SLD) · Bus schemes

1Line bayCopy link to Line bay

A line bay connects an overhead line to the buses. Figure 1 shows the default project's line bay as the design service builds it, with its devices in their order from the line gantry to the bus isolators.

The devices of Figure 1, from the line to the buses:

1. Surge arrester −F1, at the line's entry
2. Capacitor voltage transformer (CVT) −T5
3. Line isolator −Q9 with its earth switch −Q8
4. Current transformer (CT) −T1
5. Circuit breaker −Q0
6. Bus isolators −Q1 and −Q2, one to each bus of the scheme
7. Bus 1 and Bus 2 of the double main bus

The line bay carries the main and check meters of the grid connection: availability-based tariff (ABT) meters in the IEC + CEA / CBIP set, revenue meters in the ANSI / IEEE set. In a one-and-a-half breaker diameter, the line takes off between the Bus 1 main breaker and the tie breaker.

2Transformer bayCopy link to Transformer bay

A transformer bay connects an interconnecting transformer (ICT) to the buses. Figure 2 shows the default project's transformer bay as the design service builds it, with its devices in their order from the bus isolators to the transformer.

The devices of Figure 2, from the buses to the transformer:

1. Bus isolators −Q1 and −Q2
2. Circuit breaker −Q0
3. Current transformer (CT) −T1
4. Isolator −Q9 with its earth switch −Q8
5. Surge arrester −F1
6. Interconnecting transformer −T01, YNyn0 + d

The ICT's HV side carries the standby meter. In a diameter, the transformer takes off between the tie breaker and the Bus 2 main breaker.

The design's ICT at a 132 kV or 220 kV pooling substation is YNyn0 with a delta tertiary. Its HV neutral is solidly earthed, and its medium-voltage (MV) neutral is earthed through a neutral grounding resistor (NGR). A surge arrester protects its low-voltage terminal. The 400 kV unit with a split low-voltage winding is YNyn0yn0 with a delta tertiary, a switching substation's ICT at 220 kV and 400 kV is an autotransformer, YNa0d11, and a 33/11 kV transformer is Dyn11, with no HV neutral.

3Coupler, bus section and bus voltage transformersCopy link to Coupler, bus section and bus voltage transformers

A double main bus has a bus coupler bay, a breaker that joins the two buses. A single sectionalised bus has a bus-section bay, which joins the two sections: a breaker with an isolator on each side and a CT. Each bus, or each bus section, has its own voltage transformer: a CVT, or a potential transformer (PT) at a 33 kV HV level. A ring bus has no main buses and no bus voltage transformer, and each circuit has its own potential source (RUS Bulletin 1724E-300 §4.6.4).

4Future baysCopy link to Future bays

A future bay keeps space in the yard for a circuit to come. It is drawn on the SLD and kept in the yard's layout, and the design does not count it in the equipment the substation is built with. A one-and-a-half breaker diameter with a future circuit is built with two breakers, and space and foundations are kept for the third (Bus schemes, Bus schemes of the IEC + CEA / CBIP set).