| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that a low resistance is required to be inserted into a transformer ground line to apply a signal voltage for measuring insulation state or insulating of a low voltage electric line, however, a resistor of very large power capacity is required for safe flowing of a current at low-voltage earth fault, and to solve the problem that the earth fault accident in a direct grounding power distribution method which is commonly used is possible to release a large earth fault energy, causing a short circuit fire or electric shock. SOLUTION: A low resistance for applying a voltage for detecting insulation is inserted in a ground line to which one end or a neutral point of a secondary winding of a power distribution transformer is grounded. A means is provided for monitoring a current that flows the resistance. A low-voltage earth fault is recognized when the current flowing it exceeds a single line perfect earth fault current value which is calculated from the constant of a transformer primary power distribution system, and a low-voltage earth fault current limiting resistor is automatically inserted. High-voltage earth fault of primary mixing/contact is recognized when a voltage between a low-voltage electric line and the ground rises to a high voltage which cannot be generated from a low-voltage power distribution, and a low resistance is inserted. COPYRIGHT: (C)2004,JPO&NCIPI
|
