| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a ground directional relay for low voltage circuit which can surely determine the low voltage side circuit of the grounded high/low voltage transformer when the low voltage side circuit is grounded in any one of a plurality of high/low voltage transformers which are connected to the earth in common in the low voltage side winding. SOLUTION: When the low voltage side circuit of a high/low voltage transformer Tr1 or a high/low voltage transformer Tr2 is grounded, a current flowing into the bus EBL0 connected to the earth, a current flowing into a branching lead EBL1 connected to the earth, and a current flowing into a branching lead EBL2 connected to the earth, increase. For example, when the low voltage side circuit of the high/low voltage transformer Tr1 is grounded, a ground directional relay 1 for low voltage circuit obtains, with the vector arithmetic operation, the increments of the current of the grounded bus EBL0 detected with a current detector ZCT0, and the current of the branching lead EBL1 connected to the earth detected with a current detector ZCT1. Also, the relay 1 determines that the low voltage side circuit of the high/low voltage transformer Tr1 is grounded when the phase of increased current of the branching lead EBL1 connected to the earth with reference to the phase of increased current of the bus EBL0 connected to the earth is in the in-phase condition or in the lead-phase condition.</p> |
