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Which busbar arrangement is more reliable and flexible?
Main and transfer bus scheme
One and half breaker scheme
Double busbar scheme
Single busbar scheme
One and half breaker scheme
The one-and-a-half breaker scheme is considered the most reliable and flexible busbar arrangement because it provides extreme continuity of service. It requires three circuit breakers for every two circuits, ensuring that any circuit can be serviced or any busbar faulted without interrupting supply to other connected circuits.
The one-and-a-half breaker scheme is considered the most reliable and flexible busbar arrangement because it provides extreme continuity of service. It requires three circuit breakers for every two circuits, ensuring that any circuit can be serviced or any busbar faulted without interrupting supply to other connected circuits.
NCBтАЛ=1.5├ЧNcircuitsтАЛ тАФ Calculation of total breakers required relative to circuits
In this arrangement, two circuits are connected in series through three circuit breakers located between two main buses. If one bus fails, the other remains energized, and the circuits continue to receive power. Furthermore, if a circuit breaker needs maintenance, it can be bypassed without requiring a supply outage for the associated feeder circuits.
Highest level of reliability among common substation schemes.
Eliminates the need for a separate transfer bus.
High initial investment due to the high number of circuit breakers.
Ideal for EHV (Extra High Voltage) and UHV transmission substations.
High supply security during busbar maintenance.
Breaker maintenance does not interrupt power.
Fault on one busbar does not disconnect any feeder.
Expensive due to the high number of circuit breakers required.
Complex relaying and protection schemes.
Requires more physical space for installation.
EHV (Extra High Voltage) transmission substations.
Generating station switchyards.
Large interconnected power grids.
| Feature | 1.5 Breaker | Single Bus |
|---|---|---|
Cost | Very High | Low |
Reliability | Excellent | Poor |
The 'One and half' refers to the ratio of circuit breakers per feeder (3 breakers / 2 circuits = 1.5).
Double busbar schemes offer flexibility but are less reliable than the 1.5 breaker scheme under bus fault conditions.
B is correct тАФ The one and half breaker scheme provides maximum redundancy and operating flexibility by utilizing three circuit breakers for every two circuits, allowing for seamless maintenance and fault isolation.
Always remember that in the 1.5 breaker scheme, a fault on either bus bar results in zero loss of supply to the feeders, which is why it is preferred for critical transmission nodes.