| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To suppress a ground fault current of an electric circuit on a low voltage side so as to develop a suitable protection cooperation, and also to prevent a malfunction in a ground fault protection relay or a ground fault interrupter due to a harmonic current or a high frequency noise. <P>SOLUTION: A contact prevention plate 4 provided between a high voltage coil 5 and a low voltage coil 3 is B-type-grounded to a structure 11 composed of a metal body such as an iron frame of an office building or the like via a ground terminal 1e. A resistor 10 is connected to between the neutral point of the low voltage coil 3 and the ground terminal 1e, and its resistance value is set to a value in a range of 10<r<(V/3<SP>1/2</SP>)/Is[Ω] (V: a rated voltage on the low voltage side, Is: an operating current of the ground fault protection relay or ground fault interrupter). When a ground fault accident in the structure 11 occurs in the electric circuit on the low voltage side, the ground fault current is limited by the resistor 10, and is suppressed to a value decided by the protection cooperation. Further, an area where a current flows when the low voltage coil 3 is short-circuited to the contact prevention plate 4, can be restricted only to the side of the low voltage coil (the side of the short proof plate) rather than a common connection point of the resistor 10 and the contact prevention plate 4. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
