JPS54143848A - Transformer protective relaying system - Google Patents

Abstract

PURPOSE: To provide the subject system wherein the interruption of a transformer is determined by a three-winding passing current of the transformer and a two-winding passing current except the components connected to a higher harmonic generating source, and further when the outputs of these currents given to an overcurrent relay assume interrupting directions, the transformer is interrupted thereby to prevent the erroneous judgment.

CONSTITUTION: A comparator 37 generates an output in the interrupting direction of the transformer from the vector sum of three-winding current of the transformer through a differential circuit 32 and a scalar sum circuit 33. From two winding currents except the component connected to a higher harmonic generating source, a second higher harmonic component is introduced through a differential circuit 31 and the like, and a comparator 36 generates an output in the interruption preventing direction depending upon the component. A coincidence gate 38 determines theinterruption in accordance with the outputs of both comparators. On the other hand, the outputs of differential circuits 32 and 31 are introduced in overcurrent relays having level detectors 40 and 39, respectively, and when both overcurrent relays produce outputs because of more than the predetermined values of said outputs of the differential circuits, a coincidence gate 41 generates an interruption signal. According to this arrangement, an erroneous judgement due to the transient current of the higher harmonic generating source connected to the terminal of the transformer can be prevented.

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