The earth-short detecting circuit is included in the neutral line of a three phase generator in its star windings, and and has a single-phase transformer (FV') connected by its primary between earth and the generator's neutral, and a three-phase transformer (FV") connected by its primary between earth and the generator's terminals and its secondaries are connected to form an open delta winding. A voltage divider (Z', Z") is connected to the terminals of the series-coupled secondaries of both transformers. - The divider's tapping is connected via a voltage detector (1, 2), which detects the system's third harmonic, to the secondary windings common point.
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