| 摘要 |
<P>PROBLEM TO BE SOLVED: To enable an accurate detection of, by a simple structure, an insulation resistance to the earth of a low-voltage electrical path, even with an insulation monitoring signal for small electric power. <P>SOLUTION: An insulation monitoring apparatus inputs a monitoring signal having a frequency different from a commercial frequency to a Class-B grounding conductor of a transformer 1 and detects a leak current circulating to the Class-B grounding conductor via the low-voltage electrical path of this transformer and the earth. Meanwhile, by using a band reject filter to eliminate (suppress) commercial components, a major noise source, from a reference input from the Class-B grounding conductor assuming a Class-D grounding point of the low-voltage electrical path to be a reference, the apparatus extracts a reference signal B from a remaining reference input at high accuracy, the reference signal B serving as a reference for DFT computation, and accurately obtains insulation resistance components to the earth contained in monitoring signal components of the detected leak current by the DFT computation phase-synchronized with this reference signal B. <P>COPYRIGHT: (C)2010,JPO&INPIT |
