PURPOSE: To surely detect a reverse-charging state from a nonutility power-generation installation up to an electric-power supply system side when the nonutility power- generation installation is a current source-type power supply by a method wherein an impedance-load part for detection is closed periodically only during an extremely short time after a definite time by making use of an AC-voltage zero-crossing point as a reference.
CONSTITUTION: A switching control circuit 43 periodically repeat an operation to close an impedance-load part 42 for detection by turning on a switch part 41 only for an extremely short time after a definite time while the generation point of time of a zero-crossing detection pulse from an AC-voltage zero-crossing detection circuit 44 detecting a point of time when the instantaneous value of an AC voltage in a branch line 31 becomes zero is used as a reference time. Then, an operation part 46 operates the ratio of a change amount of a time when the switch part 41 of a voltage detected by a voltage-detection part 45 is turned on to a time when it is turned off. A discrimination part 47 judges the power-supply loss state of an electric- power supply system side 1 when the operated result of the operation part 46 is larger than a prescribed reference value, and it detects a reverse-charging state to the electric- power supply system side 1 from a nonutility power-generation installation 21.
YAMAZAKI KIYOMI
HIRATA MASAKI
OKI TOSHIHIKO
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