About the Bus Scheme Comparator

Bus scheme comparison evaluates the trade-offs between single-busbar, double-busbar, and breaker-and-a-half switchyard configurations for solar plant interconnection — comparing capital cost, operational flexibility, maintenance outage requirements, and protection complexity.

How to calculate it

1. 1Single bus: all feeders and transformers connect to one busbar. Simplest and lowest cost. Any bus fault or bus maintenance takes the entire switchyard out of service. Acceptable for < 5 MW plants or 11 kV connections.
2. 2Double bus with bus coupler (double bus, single breaker): two busbars connected by a bus coupler circuit breaker; each bay has a bus selector switch. One bus can be maintained while the other stays energised. Standard for 33 kV plants > 5 MW. Adds bus coupler cost and bus-selector maintenance.
3. 3Breaker-and-a-half: two busbars, three circuit breakers per two feeder bays. Each feeder is connected to both busbars through its own breaker and shares a 'middle' breaker with an adjacent feeder. Highest reliability — no feeder outage during bus maintenance. Used for 220 kV and above, or critical large plants.
4. 4Score each scheme on cost (capex per bay), availability (% uptime for a bus fault), protection complexity, and land area.

Worked example

A 50 MW, 220 kV solar plant: single-bus fails the availability requirement (utility insists on N-1 feeder continuity). Double-bus adds one bus coupler CB but allows feeder maintenance without plant shutdown — preferred. Breaker-and-a-half is specified by the grid operator for 220 kV interconnections; plant EPC must comply regardless of cost premium.

What you can calculate

• Reliability score
• CAPEX ratio
• Flexibility
• Scheme comparison

Standards & references

Frequently asked questions