| 摘要 |
PURPOSE:To protect an equipment from high-harmonic overcurrent, and improve volume efficiency and cost efficiency of an entire system by providing a high- harmonic content calculation circuit for calculating the ratio of a high-harmonic current for a fundamental wave current. CONSTITUTION:Current is led from a main 10 of a system by a current transformer 11 and sampling measurement is made by a sample/hold circuit 12. A high-harmonic content calculation circuit 15 calculates the ratio of high- harmonic current value (high-harmonic content) for the fundamental wave current contained in a detection current. The operation time from the excess of a specific value of the high-harmonic content to signal output is specified. Namely, a reverse time-delay characteristic operation function circuit 16 retains operating characteristics of an output circuit 17 and a system manager sets the characteristics from an input circuit 18. The output circuit 17 outputs an open control signal CO and opens a specific equipment of the system when a high-harmonic content exceeds a specific value. A display 19 displays current instantaneous value in the main 10, the instantaneous value of high-harmonic constituents, high-harmonic content, and errors. |
