Protection of household appliances from overvoltage and undervoltage in the electrical network. 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 expediency of such schemes is beyond doubt due to the deterioration of the services of electrical networks, the poor condition of overhead and cable power lines.

The circuit diagram of the proposed device is shown in Fig.1, the printed circuit board and the location of parts - in Fig.2.

(click to enlarge)

The machine is installed immediately after the apartment electric meter and serves to turn off the apartment electrical network in cases where the voltage exceeds the permissible 240 V and drops below 160 V. The hysteresis in both modes is 20 V.

The operation algorithm of the device is as follows: when the voltage in the network increases to 240 V, the machine turns off the load and automatically turns it on when the rated voltage is 220 V; when the voltage drops to 160 V, the machine completely turns off the load and automatically turns it on when the minimum allowable voltage of 180 V is established in the network, at which household appliances can operate. The operation levels of both modes can be set individually using resistors R2 and R3.

The basic element of the device - supervisor type KR1171SP10 (undervoltage detector) - is an electronic device that generates a signal when the monitored voltage falls below the allowable level. The device includes a measuring bridge with a zener diode, a comparator and an open collector transistor. When the supervisor is triggered, the transistor goes into a conducting state. Chips are produced in plastic cases KT-26. More details about the types and electrical parameters of supervisors can be found in [1] or on the Internet.

The device circuit contains: a mains rectifier VD1-VD4, a capacitor C1 with a voltage divider R1 (common) and R2 and R3 (trim), to the conclusions of which supervisors are connected, a step-down rectifier for the operation of the electrical circuit VD5VD8, C3, C4, a zener diode VD9, transistor switches VT1, VT2, emitting LED HL1, mounted on the body of the device, which serves to monitor the state of operation of the electrical circuit and optocoupler type AOU103V, which controls the actuator - a magnetic starter of the 1st magnitude.

Operating principle. In standby mode, when the mains voltage does not exceed the allowable value, the supervisor D1 is open, respectively, the transistor VT1 is open. As a result of the passage of a constant voltage from the zener diode VD9 through the open junctions of the transistors VT1, VT2, the current limiting resistor R8, the control LED HL1 and the optocoupler LED VU1, the LEDs light up and the actuator is activated - the magnetic starter P1, through the contacts of which all apartment wiring is connected. When the mains voltage exceeds the maximum allowable level, the supervisor D1 closes, the transistor VT1 closes, the current flow through the optocoupler LED stops, as a result, the power supply circuit of the P1 starter winding is broken. The actuator is de-energized, and all apartment wiring with all consumers is disconnected from the mains.

When the mains voltage drops below 160 V, supervisor D2 is activated.

As a result, the transistor VT2 closes, the current does not flow through the control LED and the optocoupler, which ultimately leads to a de-energization of the P1 starter winding and disconnection of all consumers from the mains.

All parts of the machine, except for the magnetic starter and the control LED, are placed on a printed circuit board made of foil fiberglass. Capacitors C1, C3 imported type XE224, resistor R1 type MLT-1, all the rest - MLT-0,25, R2, R3 type SPZ-16 or SPZ-27, 28a for a power of 0,25 watts. Capacitors C2, C4 type K50-24. Diode bridges VD1-VD4, VD5-VD8, VD10VD13 type KTs407A. Zener diode VD9 type D814G in a metal case. LED HL1 any with a constant forward current of at least 30 mA. As an executive relay, a magnetic starter of the 1st magnitude was used, the contacts of which are of sufficient power to switch the connected load.

To set up the machine, an autotransformer of the LATR type is required. Having set a voltage of 220 V at the output of the autotransformer, the assembled device is connected.

Any multimeter measures the voltage at the zener diode VD9 (it must be at least 11 V), then measure the voltage at pins 1 of the supervisors D1 and D2 (it should be about 11 ... 12 V, otherwise, moving the trimmer resistors R2 and R3 , set the required voltage, while the machine turns on, the control LED lights up and the magnetic starter is activated). Then, a voltage of 240 V is set at the LATR output, the trimming resistor R2 is used to turn off the starter, and the control LED goes out.

By smoothly reducing the voltage at the LATR output, they control the moment of switching on, the LED lights up, the starter is activated.

This should happen at a voltage of 220 V. Next, set the voltage to 160 V at the output of the autotransformer and, by rotating the engine of the trimming resistor R3, set the moment for turning off the machine. When the voltage at the input of the device increases to 180 V, the machine should turn on. This completes the adjustment.

References:

1. Radioamator-Designer. - 2000. No. 2. - P.28.

Author: V. Lazovik

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