PURPOSE: To prevent erroneous interruption due to counterflow of regenerated power by providing a regenerative power judging section for elevator, a reverse power judging section for judging reverse power based on added power flow from a generator and an elevator, and the like.
CONSTITUTION: Reverse power flow IG from a generator 4 and reverse power flow IE due to regenerative power of an elevator 6 are combined through a metering current transformer 9 to produce (IG+IE). Regenerative current-IE from a metering current transformer 12 is also fed to an adding section 15 thus cancelling reverse power flow due to regenerative power according to formula 1. A reverse power judging section 16 operates based on the current according to the formula I and voltage fed from a metering potential transformer 10. When an elevator 6 operates on a forward current I'E sum of the forward current and the reverse current IG from the generator, i.e., (IG-I'E), flows through the adding section 15, while current from the current transformer 12 for detecting forward current of elevator does not flow through the adding section 15 because contacts 14a, 14b are turned ON, OFF respectively. The reverse power judging section 16 is operated by the current (IG-I'E).
TANAKA MORIHISA
TOKU MITSURU
