PURPOSE: To reduce displacement from an actual phase synchronization point due to slip fluctuation by permitting the transmission of a closing signal over a breaker when the absolute value of phase difference in electric wires at both ends of the breaker reaches or is less than a value obtained by multiplying a reference angle by the absolute value of frequency difference and a closing dead time. ;CONSTITUTION: A phase difference detector 11 detects the phase difference of AC power in electric wires at both ends of a breaker. First and second voltage/frequency conversion circuits 12, 13 convert voltages VG, VL into generator frequency and commercial frequency, and a frequency difference detector 14 detects the absolute value of the difference of these frequency. The phase-angle arithmetic means of a command- emitting time arithmetic circuit 16 obtains phase angles until the phase synchronization points of both power after the time of detection by multiplication by the absolute value of frequency difference and a closing dead time. A command-signal generating means compares the absolute value of phase difference detected and the arithmetically operated phase angles, and emits a command signal when the former value reaches the latter value or less. Accordingly, displacement from an actual phase synchronization point due to slip fluctuation can be reduced.;COPYRIGHT: (C)1993,JPO&Japio
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