Priority switching on and off loads. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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When turning on and off the power transformers that feed the thyristor units, significant overvoltages occur due to the interruption of the magnetizing currents. To protect the thyristor blocks from overvoltage, it is proposed to use separating switches with priority switching on and off of the power transformer and the thyristor block. The electrical connection diagram of the separating switches is shown in Fig.1.
Whenever SA1 or SA2 is turned on, the power transformer T1 will be turned on first, and then the thyristor unit. When any of the switches SA1 or SA2 is turned off, the thyristor unit will be turned off first.
For priority switching on and off of three power sources, it is necessary to connect the power sources and switches according to the diagram in Fig.2.
Whichever switch is closed first (SA1, SA2 or SA3), voltage will be applied on line 1, then on line 2, and after all switches are closed, on line 3, the de-energization will be in the reverse order, regardless of which switch was open first and which one last.
Toggle switches of the TBI-4 type (250 W, 220 V, 5 A) were used as switches. For more powerful loads, it is necessary to use switches that allow switching high currents.
Author: V.F. Yakovlev
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