FIELD: electrical engineering.
SUBSTANCE: device for protection against single-phase earth faults in compensated medium voltage electrical networks contains the zero-sequence current sensor, which is connected to the first band frequency filter, zero sequence voltage transformer, which is connected to the second band-pass frequency filter, differentiator, first and second RMS calculation units, it additionally contains the starting unit according to the level of higher harmonics in the zero-sequence current, the unit for calculating the ratio of two quantities, the comparison circuit with a setpoint, the triggering unit for a zero-sequence voltage, logic element AND. At the same time, the output of the first band frequency filter is connected to the input of the first unit for calculating the RMS value, the output of which is connected to the input of the starting unit according to the level of higher harmonics in the zero-sequence current and to the first input of the unit for calculating the ratio of two quantities, the output of the second band frequency filter is connected via the differentiator to the input of the second RMS calculation unit, the output of which is connected to the second input of the ratio calculation unit of two quantities, the output is connected to the input of the comparison circuit with the setpoint, the output of the starting unit according to the level of higher harmonics in the zero sequence current is connected to the first input of the logic element AND, the output of the comparison circuit with the setpoint is connected to the second input of the logic element AND, the third input of which is connected to the output of the starting body via zero-sequence voltage, the input of which is connected to the output of the measuring voltage transformer of zero-sequence.
EFFECT: increased selectivity and sensitivity of protection against single-phase earth faults and expanded field of application in compensated medium voltage electrical networks.
1 cl, 6 dwg
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