Automatic supply of the correct phase sequence to the three-phase consumer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network, uninterruptible power supplies
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The disadvantage of the device for protecting a three-phase consumer from changing the phase sequence [1] is that if the phase sequence of the supply network is incorrect, the magnetic starter does not turn on and power is not supplied to the load. In this case, to turn on the load, it is necessary to change the phase sequence of the supply network. However, manual operation is difficult, especially when the power supply and remote controlled loads are in hard to reach places.
To automatically supply the consumer with the correct phase sequence, regardless of the phase sequence of the supply network, a device is proposed, the diagram of which is shown in Fig. 1.
The device contains thyristors VS1 and VS2, in the circuits of which the relays K1 and K2 are connected, the control transformer T1, the secondary winding of which is connected to the thyristor control circuit through the diode VD1 (the beginning of the winding) and the diode VD3 (the end of the winding), and the middle point of the winding is connected through the zener diode VD2 to the cathode circuit of thyristors. The beginning of the primary winding of the transformer T1 is connected to the lagging phase, and the end is connected to the leading phase, to which the cathodes of the thyristors VS1 and VS2 are connected.
The device works as follows. When the SB1 "Start" button is pressed and the phase sequence is correct (in diagram A, B, C), the duration of the half-cycle AB (voltage Uk1 Fig. 2) applied to the relay coil K1, and therefore to the anode-cathode terminals of the thyristor VS1, and the voltage applied to the control electrode of the thyristor VS1 (Uу) of the half-cycle CA during the first 60° of the half-cycle AB are the same.
As a result, the thyristor VS1 turns on, the relay K1 is activated and contacts K1.1 supplies voltage to the coil of the KM1 magnetic starter. The KM1 starter turns on, and the mains voltage is supplied to the consumer. At the same time, the duration of the half-cycle CB (Fig. 3) applied to the control electrode of the thyristor VS2 (half-cycle AC), due to the signal delay by the zener diode VD2 by 60 ... 90 °, starting from the half-cycle, does not match, so the thyristor VS2 does not turn on may, and therefore, turn on the relay K2, which turns on the starter KM2.
If the phase sequence is incorrect (in Fig. 1 (B), (A), (C)), the duration of the half-cycle (B) C (Fig. 4), the voltage Uk2 applied to the coil K2, and therefore to the anode terminals -the cathode of the thyristor VS2, and the voltage applied to the control electrode VS2 (Uy) (half-cycle C (A)) during the first 60 ° of the half-cycle (B) C, coincide, as a result, the thyristor VS2 turns on, the relay K2 is activated, the contacts of which are K2.1. 2 include the KM5 starter. The mains voltage is supplied to the consumer, and the phase sequence is automatically changed from incorrect to correct. At this time, the action of the half-cycle (B) (A) (Fig. 1), applied to the control electrode VS2 (half-cycle C (B)), due to the signal delay by the zener diode VD60 by 90 ... 1 °, starting from the half-cycle, does not matches, so the thyristor VS1 cannot turn on, which means that relay K1 and starter KMXNUMX will not turn on.
Thus, manual operations to change the phase sequence are eliminated.
A device assembled from serviceable elements and without errors does not require adjustment.
Details. Transformer T1 is assembled on a Sh16x24 core. The primary winding contains 4650 turns of PEL wire 0,1 mm, the secondary - 2x145 turns of PEL-1 wire 0,42 mm. Relay K1 and K2 type RPU-05 220 V. Thyristors VS1 and VS2 type T112-10-8.
References:
- Yakovlev V.F. Device for protecting a three-phase consumer from changing the phase sequence//Electrician. - 2003. No. 12. - P.15.
Author: V.F. Yakovlev
See other articles Section Protection of equipment from emergency operation of the network, uninterruptible power supplies.
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