Motor speed regulating backup power supply automatic input circuit

When the unit fails and loses power, circuit breaker QF trips and contactor KM2 releases
. KM, pull-in (assuming there is power from the external grid), switches the power supply of the speed-regulating motor from the unit to the grid power supply. At the same time, the governor
performs an emergency automatic shutdown to prevent the unit from causing a speeding accident.
    When installing and debugging this control circuit, attention must be paid to the contactors KMi and KM: when the power is lost and released, the main
contact must act one time earlier than the auxiliary contact, which can be mechanically adjusted. Otherwise, when the circuit breaker QF
is closed during paralleling, the grid power supply and the unit power supply will cause a short circuit accident.