| 摘要 |
In each case one power circuit breaker and one current transformer is allocated to the connections of the differential protection device. The secondary windings of the current transformers are connected to a differential relay. This differential relay triggers the associated power circuit breaker when the sum of the currents in the protection object is not equal to zero. An additional circuit is supplied with signals which are derived from at least one transformer secondary current (i1, i2) and the current sum (iDIFF) for both half-cycles. These signals are logically combined. A signal which inhibits the tripping of the associated power circuit breaker is present at the output (A) of the additional circuit when the signal which is derived from the sum current (iDIFF) exceeds an associated response threshold later in time than the signal which is derived from the transformer secondary current (i1, i2). The additional circuit stabilises the differential protection device such that incorrect tripping resulting from a greatly different transfer function of the current transformers is prevented. <IMAGE> |
