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Air-Insulated
Substations —
Bus/Switching
Configurations
3.1
Single Bus (Figure 3.1) ......................................................
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3.2
Double Bus, Double Breaker (Figure 3.2)........................
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3.3 Main and Transfer Bus (Figure 3.3) .................................
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3.4
Double Bus, Single Breaker (Figure 3.4) ..........................
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3.5
Ring Bus (Figure 3.5).........................................................
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3.6
Breaker-and-a-Half (Figure 3.6) .......................................
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3.7
Comparison of Configurations .........................................
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Various factors affect the reliability of a substation or switchyard, one of which is the arrangement of the
buses and switching devices. In addition to reliability, arrangement of the buses/switching devices will
impact maintenance, protection, initial substation development, and cost.
There are six types of substation bus/switching arrangements commonly used in air insulated substa-
tions:
1. Single bus
2. Double bus, double breaker
3. Main and transfer (inspection) bus
4. Double bus, single breaker
5. Ring bus
6. Breaker and a half
3.1 Single Bus (Figure 3.1)
This arrangement involves one main bus with all circuits connected directly to the bus. The reliability
of this type of an arrangement is very low. When properly protected by relaying, a single failure to the
main bus or any circuit section between its circuit breaker and the main bus will cause an outage of the
entire system. In addition, maintenance of devices on this system requires the de-energizing of the line
connected to the device. Maintenance of the bus would require the outage of the total system, use of
standby generation, or switching to adjacent station, if available.
Since the single bus arrangement is low in reliability, it is not recommended for heavily loaded
substations or substations having a high availability requirement.