DEVICE PROTECTING FROM SINGLE PHASE-TO-GROUND FAULT OF MEDIUM VOLTAGE DISTRIBUTION CIRCUIT Russian patent published in 2017 - IPC H02H3/16 H02H3/26 

FIELD: electricity.

SUBSTANCE: protection device contains matching current and zero- sequence voltage converters, band-pass frequency filters, a differentiator, a phase comparison circuit of two values, a zero-sequence voltage start-up unit, a short ground fault memory block that includes operative and long-term memory elements with two inputs - a recording one and an erasing one, the first time delay element, a short-time pulse generator on the front edge of the input signal, the first AND gate, an isolation breakdown meter, a control block of the dead-time pause duration, a zero-sequence current directional protection unit, the second and the third AND gates, the first and the second inhibition gates with one informational and two inhibiting inputs each, an OR gate, the second time delay element, four output relays. The output of the phase comparison circuit of two values is connected to the inputs of the time delay element, of the short-time pulse generator on the front edge of the input signal, of the control block of the dead-time pause duration, and to the informational input of the second inhibition gate. The recording input of the working storage element is connected to the output of the first time delay element. The erasing input is connected to the output of the short-time pulse generator on the front edge of the input signal. The output of the working storage element is connected to the first input of the first AND gate, which output is connected to the isolation breakdown meter and to the recording input of the long-term memory storage. The first output of the control block of the dead-time pause duration is connected to the first input of the second AND gate and to the first inhibiting inputs of the first and the second inhibition gates, and the second output is connected to the first input of the third AND gate and the second inhibiting inputs of the first and the second inhibition gates. The output of the zero-sequence voltage start-up unit is connected to the second inputs of the first, second and third AND gates. The inputs of the zero-sequence current directional protection unit are connected to the outputs of the matching current and zero-sequence voltage converters respectively, and the output is connected to the informational input of the inhibition gate. The output of the long-term memory storage is connected to the first output relay, the outputs of the second and the third AND gates are connected to the second and the third output relays respectively. The outputs of the first and the second inhibition gates are connected to the inputs of the OR gate which output is connected to the fourth output relay through the second time delay element.

EFFECT: increased selectability and stability of the operation of protection of medium voltage 6-35 kV of electric networks from single-phase-to-ground faults.

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