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Apparatus for earth short fault identification (earth leakage current detection) in three-point pulse- controlled rectifier systems by modified neutral point current measurement in the zero and full-voltage states
Apparatus for earth short fault identification (earth leakage current detection) in three-point pulse- controlled rectifier systems by modified neutral point current measurement in the zero and full-voltage states
The invention relates to the identification of an earth short fault in a three-phase three-point pulse-controlled rectifier system with a current transformer 20 in the switching connection 15 which leads to the capacitive centre point 7 of the output voltage. In this case, the measurement of the neutral point current also includes ampere turns of currents, for example of the mains phase currents, which add up to zero when no fault is present and thus have no influence on the measurement result. If an earth short occurs, a resultant primary flow is formed, which is the sole factor governing the transformer output signal in intervals in which the converter is in a free-running or full-voltage state, and this transformer output signal is converted to an earth short fault signal 27, by means of a comparator 23 and interlock logic 25, which switches on the output 24 of the comparator 23 only when the converter is free-running or is in the full-voltage switching state. IMAGE
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