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A 1200 A 3-pole 115,000 V breaker at a generating
station in Manitoba, Canada.
Electrical power transmission networks are protected
and controlled by high-voltage breakers. The
definition of "high voltage" varies but in power
transmission work is usually thought to be 72,500 V
or higher, according to a recent definition by the
International Electrotechnical Commission (IEC).
High-voltage breakers are nearly always
solenoid-operated, with current sensing protective
relays operated through current transformers. In
substations the protection relay scheme can be
complex, protecting equipment and busses from
various types of overload or ground/earth fault.
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