Powerful step AC voltage stabilizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Powerful step AC voltage stabilizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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In some areas, especially rural areas, it is not uncommon for the mains voltage to change from 220 to 160 ... 170 V during the day.

The idea of developing a powerful AC voltage stabilizer came to me when, due to such "stability" of the network, the refrigerator failed, and the microwave oven refused to work at a voltage of less than 200 V.

A powerful step AC voltage stabilizer is designed to maintain the network at a level of 220 V ± 10% when the mains voltage drops to 160...170 V.

The basic model is designed for loads up to 1,3 kW, but can be easily converted to loads up to 2 kW or more. The stabilizer is assembled from unified parts, cheap to manufacture, easy to set up.

(click to enlarge)

Consider the principle of operation of the stabilizer according to the schematic diagram (see figure). When the mains voltage drops, the control device, assembled on the LM 324 chip, connects the T1 transformer through the triac VS1, which is connected as a step-up autotransformer. The voltage of the secondary winding T1, which is approximately 20 V, is added to the mains voltage.

With a further decrease in the mains voltage, transformer T2 is connected, and then T3. The transformers add a total of approximately 60 V to the mains voltage.

Thus, when the mains voltage is reduced to 160 V, the load will be approximately 220 V.

When the mains voltage rises from 160 to 220 V, the control device switches off T1 ... T3 in series. A voltage of 205...242 V is maintained on the load throughout the entire regulation range.

The control device is based on a quad op-amp of the LM254 type. All four channels are assembled according to the same scheme, so let's consider the operation of channel 1.

Op-amp DA 1.1 is included in the comparator mode with positive feedback. The mains voltage through the diode bridge VD1, the divider R3, R4, the diode VD1 ', the resistor R3 ' is fed to the non-inventing input of the op-amp, where it is compared with the reference voltage taken from the zener diode VD3.

If the voltage Uin, taken from the divider R3, R4, is lower than the reference, relay K1 is turned off and its n.c. contacts K1.1 through the triac VS1 turns on the transformer T1, adding about 20 V to the mains voltage. If Uin is higher than the reference, K1 trips and turns off the voltage boost.

With the ratings of the elements indicated in the diagram, the operation / release of the relay K1 of the control channel occurs when the mains voltage changes by about 10 V. The hysteresis can be changed by selecting the resistance of the resistor R4'.

Channel 4 is used to delay the connection of the load at the time of the end of the transients in the stabilizer at the initial start-up, as well as to disconnect the load from the network if it is impossible to provide more than 200 V at the output of the stabilizer. The capacitance of the capacitor C1' in channel 4 is 22 microfarads.

Transformers T1 ... T3 serial type TN 60-220 / 12750 or any other, designed for a power of 160 ... 250 W with a voltage on the secondary winding of 20 ... 24 V at a current of 6 ... 10 A. T4 - any low power at 24 V.

Triacs VS1 ... VS3 type KU208 G, TS 10 and others for a current of 5 ... 10 A and a voltage of 400 V. Relays K1 ... K4 RES-9, RES-6, RES-22 for a winding voltage of 24 V. Relay K5 - RP21-UHL4A ~ 220 V, all four groups of contacts are paralleled. Resistors R4, R6, R8, R10 subscript SPZ-1, SPZ-22 or other small-sized resistors - MLT.

Connections of the power part of the stabilizer should be made with flexible copper conductors with a cross section of 2,5 mm2.

The stabilizer is mounted in a metal case with ventilation holes.

The top cover is covered with a decorative self-adhesive film. It has a socket and LED HL1. Triacs and relays are installed inside the housing on a fiberglass plate. To eliminate interference, it is better to place the printed circuit board of the control device away from transformers and power circuit wires.

During long-term operation of the stabilizer with rated power, it is necessary to provide for forced cooling, for example, with a mini-fan from a computer (the fan is not shown in the diagram).

To establish the device, LATR and a voltmeter are needed. The network is connected to the stabilizer through the adjustable LATR output. An incandescent lamp of 200 ... 300 W is used as a load. The voltmeter is connected in parallel with the load. The trimming resistor sliders must be set to the middle position. Turn on the stabilizer without load.

By rotating the potentiometer R10 of channel 4, relay K5 is activated, and by rotating the potentiometers R4, R6, R8, relays K1, K2, K3 are activated. Connect load and voltmeter. Lower the voltage at the load to 210 V with the LATR. Slowly rotating the resistor R4, turn on T1.

Reduce the voltage at the load with LATR to 210 V. Repeat the above operation for channels 2 and 3. Set the voltage for switching off the stabilizer from the load by channel 4 at 200 V.

Repeat the setting several times until the desired result.

Note. If desired, one of the channels can be configured to lower the mains voltage, for which the contacts of the control relay should be replaced with normally open ones, and the ends of the secondary winding of the transformer should be swapped, turning on the transformer as a step-down one.

Author: I.A. Malenkov

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