Protection of REA against voltage surges. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Protection of equipment from emergency operation of the network
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I propose a device for protecting equipment from power surges. Unlike those described earlier, the proposed device does not turn on again when the normal mains voltage is restored. Switching on occurs only after pressing the "ON" button. This is necessary when the equipment is turned on unattended, and the mains at this time begins to “jump” or turn off repeatedly.
We will consider the operation of the device according to the principle diagram. The chain C1-R1 creates, when the button SB1 is closed, the starting current of the relay K1. The current through the C2-R3 chain keeps the relay on. Capacitance C2 is selected so that when the mains voltage drops to 160 V, the relay turns off.
(click to enlarge)
Emergency shutdown when the voltage rises to 250 V occurs due to the shunting of the relay winding with a thyristor VS1. VS1 opens under the control of optocoupler VU1. Zener diodes VD10, VD11 and resistor R4 are selected so that VS1 opens at a mains voltage above 250 V. Optocoupler VU1 must be with a control current of about 20 mA. It can be replaced by a small isolating transformer. It is switched on by the secondary winding instead of R2. Relay K1 can be of any type with contacts that can withstand the maximum load current (RES9, RES22, REN33).
For each type of relay, it is necessary to select the capacitances: C1 - for reliable switching on of the device and C2 - for switching off when the voltage drops to 160 ... 170 V. The total stabilization voltage VD10, VD11 should be about 330 ... types, for example D340.
Instead of the VD6...VD9 bridge, you can use one diode (KD209) connected in series with VD10, VD11. In this case, only one polarity of the alternating voltage will be controlled, which is sufficient in most cases.
Diode VD5, connected in series with the winding of the relay K1, reduces the time it turns off when the thyristor VS1 is opened.
The speed of the device was not measured, but approximately it is several tens of milliseconds (depends mainly on the type of relay K1) and reliably protects the load from burnout. C4 eliminates false alarms of the device from RF interference.
Six such devices I have assembled show high reliability in operation.
Author: A. Zelenin, Chelyabinsk region, Kartaly, Lenin street; Publication: N. Bolshakov, rf.atnn.ru
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