A Manually-Operated Spring Mechanism for Medium Voltage Oilless Circuit Breakers

Magnetic oilless circuit breakers rated 2,300 to 15,000 volts require high contact closing speeds in order to prvent excessive arcing during closing. As these contact speeds cannot be obtained manually, it has never been possible to operate magnetic circuit breakers of this class by manual mechanisms of the type frequently used to operate oil circuit breakers. In every case where medium voltage magnetic circuit breakers were applied, it was necessary, therefore, to install a reliable source of closing power. This requirement constituted a serious application handicap in some locations where a reliable source of closing power (normally storage batteries) is difficult and expensive to install. This paper describes a new type of mechanism for operating magnetic oilless circuit breakers rated 2,300 to 15,000 volts, which has been developed especially for such applications. Energy is manually supplied to this mechanism where it is stored in heavy compression springs until it is released to close the circuit breaker. Unlike previous mechanisms, when this mechanism is released, the springs transfer their energy to a rotating mass which in turn drives the circuit breaker contacts. As this rotating mass accelerates until the circuit breaker contacts meet, its entire energy is available for closing and latching the circuit breaker against the magnetic retarding forces of high current short circuits if the circuit breaker should be closed accidentally on a faulted circuit.