| 摘要 |
PROBLEM TO BE SOLVED: To perform high precision and high-density insulation monitoring using a small-power monitoring signal, and to obtain a stable monitoring output without being affected by instantaneous noise. SOLUTION: The monitoring signal of a frequency different from a commercial power frequency is injected into a class-B grounding line 4 of a transformer 1, a leak current returning to the class-B grounding line through the low-voltage side electric path thereof and the grounding is detected, unnecessary components are removed, and a measurement signal corresponding to the monitoring signal component of the leak current is detected. A reference signal corresponding to the injected monitoring signal is detected from a reference input from the class B grounding line with a class-D grounding point of the low-voltage side electric path as a reference. The ground insulation resistance component included in the measurement signal is obtained by DFT operation in synchronization with the reference signal using the measurement signal of n (>m) cycles of each reference signal shifted by m cycles of the reference signal. The output is monitored in a time sequential manner. When the insulation resistance value of this time is increased from a previous insulation resistance value by a prescribed rate or higher, the monitoring output is stabilized by applying the weighting of less than 1 to the value of this time. COPYRIGHT: (C)2010,JPO&INPIT |
