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Page 249

| disconnecting power transformers from an electrical system. Where there are internal faults, it operates by opening the circuit breakers on both the input and output sides of the transformer. Since this method of protection is obtained by connecting the elements of induction-type-overcurrent relays differentially, the relay operation depends on the difference in magnitude or direction of the currents supplied by current transformers on both sides of the power transformer (Fig. 13-10). |

| Figure 13-10 Differential relay protection: (A) Difference in current on either side of protected equipment is detected by current transformers and will not pass through the relay-actuating coil, 11 - 12, if 11 = 12; (B) wiring diagram showing internal connections. |

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