A: APPENDIX
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL A–3
Once again, if the polarity of one of the phases is out by 180°, the magnitude of the
resulting vector on a balanced system will be out by a factor of 1.73.
On a three wire supply, this configuration will always work and unbalance will be detected
properly. In the event of a single phase, there will always be a large unbalance present at
the interposing CTs of the relay. If for example Phase A was lost, Phase A would read zero
while Phase B and C would both read the magnitude of Phase C. If on the other hand,
phase B was lost, at the supply, Phase A would be 180° out-of-phase with Phase C and the
vector addition would equal zero at Phase B.
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