What Are Generator Circuit Breakers?
Generator circuit breakers represent
another class rated for very high continuous currents and short
circuit currents, typically at generator voltages. Generator breakers
are incorporated into generator bus ducts and can include other
switchgear components for measuring current, detecting faults, and
grounding.
Generator breakers are available up to
50 kA nominal current and up to 220 kA interrupting current. Two
technologies are employed—air blast at the higher ratings and SF6
self blast at the lower and medium power levels (up to 120 kA). For
nominal currents above 20 kA, the generator breaker is usually
equipped with a forced cooling system, using water, for example.
Generator breakers have been available since the 1960s.
Advantages of using generator
breakers include the following:
Reduced station cost by eliminating
station transformers and increasing station layout flexibility.
Simplification of operation, especially
during commissioning and recommissioning; this is because the
generator can be handled as a separate unit, isolated from the main
and unit transformers.
Fault protection between the generator
and transformer. Two zones of protection are created and generator
faults are cleared by the opening of the generator breaker alone.
Unbalanced load protection of the
generator.
Protection of the generator from
transformer faults.
Reliability/availability increase.
Historically, generator circuit
breakers have been of air-blast design with pneumatic operators. This
is the technology still used today for large nuclear and fossil fuel
power plants (up to 1500 MW), and large pumped storage installations.
The design has a tubular housing and is
horizontal. Newer designs utilize SF6 self-blast technology and
hydraulic operators. These are rated for application to smaller power
plants (gas turbine/cogen, for example) from 60 to 400 MW and smaller
pumped storage installations.
PARTS OF GENERATOR CIRCUIT BREAKERS
Outline and interrupter details of a
generator air-blast circuit breaker-type DR, 36 Kv, up to 50 kA with
forced cooling, 200 kA.
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