| 摘要 |
PROBLEM TO BE SOLVED: To detect power supply voltage failure under both conditions where only one phase has interruption and phases are in a reverse order. SOLUTION: A power supply voltage information generating circuit 41 detects information corresponding to the magnitude of the voltage values of the respective phases R, S, T of a three-phase AC power source 1 to output power supply voltage information signals Rmax-Tmin. A failure detecting signal generating circuit 42 previously keeps information based on the magnitude of the voltage values of the respective phases R, S, T when the three-phase AC power source 1 is under a normal condition, and outputs the information as failure detecting signals Rmax*-Tmin*. A determining circuit 43 compares the power supply voltage information signals Rmax-Tmin with the failure detecting signals Rmax*-Tmain* at regular intervals, and outputs a power supply voltage failure signal 101 when these signals are different from each other.
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