A device for protecting a three-phase consumer from changing the phase sequence. Scheme, description

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A device for protecting a three-phase consumer from changing the phase sequence. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies

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The proposed device will protect a three-phase consumer from changing the phase sequence and eliminate violations of technological parameters and equipment failure. At the same time, the device will protect the consumer from the breakage of any of the phases of the supply network.

The electrical circuit of the device is shown in Fig.1.

Device for protecting a three-phase consumer from changing the phase sequence

The device contains a thyristor VS1, in the circuit of which the relay K1 is connected, a control transformer T1, the secondary winding of which, through the diode VD1 and the zener diode VD2, is included in the control circuit of the thyristor VS1. The zener diode VD2 serves to delay the control signal by 60 ... 90 ° from the beginning of the half-cycle.

The device works as follows. When the SB1 "Start" button is pressed and the phase sequence is correct (according to the scheme A, B, C) during the half-cycle AB, the voltage Uk1 (Fig. 2) applied to the relay coil K1, and hence to the anode-cathode gap VS1, and the voltage applied to the control electrode of the thyristor VS1 (Uу) - half-cycle CA, coincide during the first 60 °. Therefore, the thyristor VS1 turns on and, accordingly, the relay K1 turns on, which, with its contacts K1.1, supplies voltage to the coil of the KM1 magnetic starter. The starter turns on, and the mains voltage is supplied to the consumer.

Device for protecting a three-phase consumer from changing the phase sequence

When the phase sequence of the mains is changed, as shown in Fig. 3, the half-cycle voltage (V) (A) is applied to the relay coil K1. The voltage at the thyristor cathode does not match the voltage at the control electrode Uy (half-cycle C (B)), relay K1 does not turn on, and therefore the magnetic starter does not turn on either. The mains voltage is not supplied to the consumer. To restore the power supply, phases B and C must be reversed.

Device for protecting a three-phase consumer from changing the phase sequence

The adjustment device is not required.

Details. Transformer T1 is assembled on a Sh16Ch24 core. Primary winding - 4650 turns PEL-1 0,1 mm; secondary - 145 turns PEL-1 0,42 mm. Relay K1 type RPU-0,5 220 V. Thyristor VS1 type T112-10-8.

Author: V.F. Yakovlev

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