An economical device for protecting equipment from mains voltage fluctuations. 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 device for protecting household equipment from voltage surges in the mains, the circuit of which is shown in the figure, consumes only 2,2 W, even less than the operation power of the RPU-2 relay used here. In addition, it, unlike thyristor-based protection devices, provides galvanic isolation of the load from the mains.

The protection device is turned on with the switch SA1, while the HL1 LED lights up, signaling the transition to standby mode and the readiness of the device to connect the load.

Then the SB1 "Start" button is pressed, and the voltage from the secondary winding of the transformer T1 is supplied to the VT4VD9R14 stabilizer, which supplies the control unit. Through the K1C8R18R19 circuit, a high-level pulse enters the base of the VT5 transistor, briefly opening it. The short circuit relay is activated, its contacts K3.1 open, and the contacts KZ.2 switch. Capacitors C5 and C6 begin to charge through resistor R15 to a voltage across capacitor C3 of approximately 14 V. The time the short circuit relay is on is greater than the time constant for charging capacitors C5 and C6. After that, relay K3 releases, its contacts return to their original state. As a result, the sum of the voltage on the capacitors C2, C5 and at the output of the stabilizer, equal to approximately 6 V, is applied to the winding of relay K20. Relay K2 is activated and held in this state by the current flowing through the VD11R17K1.1 circuit, its contacts K2.3-K2.6. 2.1 connect the load to the network, and contacts K1 block the button SBXNUMX "Start".

Diodes VD10 and VD11 are different: VD10 is silicon, and VD11 is germanium, so that a voltage of the correct polarity is applied to the oxide capacitors C5 and C6.

After the relay K2 is activated, its contacts K2.2 and K2.7 open, the HL1 LED goes out. A current flows through the diode VD10, limited by the resistance of resistors R15 and R16. The resistance of the resistor R16 is chosen in the range of 20-100 kOhm. Selecting the resistor R17, set the current, 15 ... 20 mA higher than the release current of relay K2.

If the voltage in the network exceeds the set limit (in our case, 255 V), the current passing through the VD3-VD5R2R3 circuit increases sharply, and accordingly, the current of the control electrode of the trinistor VS1 also increases. It opens, relay K1 is activated. Its contacts K1.1 switch, opening the power supply circuit of the winding of the relay K2, which, with its contacts K2.3-K2.6, disconnects the load, and contacts K2.2 connects the HL1 LED, which signals the operation of the protection device. The VD1R1 circuit limits the current through the HL1 LED.

To protect the equipment from low voltage in the network (in our case, 180 V or less), a Schmitt trigger is used, assembled on transistors VT2 and VT3. Resistive divider R12R13 reduces the voltage at its input, and capacitor C2 acts as a smoothing filter. If the voltage in the mains has become less than the set level, the Schmitt trigger switches (transistor VT3 closes, and VT2 opens), transistor VT1 opens and turns on relay K1.

Capacitor C8 is connected to the connection point of the anode of the trinistor VS1 and the collector of the transistor VT1 so that there is no temporary switching of the contacts of the relay K2 when the "Start" button SB1 is pressed if the mains voltage does not meet the established standards. In this case, either the trinistor or the transistor is open and shunts the C8R18R19 circuit, as a result of which the VT5 transistor does not open and, accordingly, the K2 relay does not work. If the mains voltage does not correspond to the norm, when the "Start" button is pressed, the contacts of relay K1 switch and the HL2 LED lights up, signaling that the mains voltage is out of range.

The protection device uses a homemade network transformer. It is made on an annular magnetic core wound from permalloy tape 32 mm wide and 0,2 mm thick. The outer diameter of the magnetic circuit is 40 mm, the inner diameter is 25 mm. Outside, the magnetic core is insulated with a layer of varnished cloth, over which the primary winding is wound evenly along the entire length, layer by layer, containing 3000 turns of wire PEV-2 0,15. It is also wrapped with a layer of varnished cloth, and then the secondary winding is wound, which contains 160 turns of PEL 0,51 wire. The finished transformer is also insulated with a layer of varnished cloth or other insulating material.

Diodes KD105V (VD1, VD2) can be replaced by KD105G, diodes D7A and D226G - by any of these series. We will replace the KT342V (VT3) transistor with KT3102G or KT3102E, and KT829A (VT5) with any of this series. The KT815B transistor (VT4) should be installed on an aluminum heat sink plate 6 mm thick and with an area of ​​at least 6 cm0,25. LEDs can be used any. Fixed resistors - MLT, which can be replaced with similar power of 0,5 and 5 W, tuning - SP1-5V. Oxide capacitors C6, C1000 can be replaced with one with a capacity of XNUMX microfarads for the corresponding voltage.

The device can use the relay K1 RES55A versions RS4.569.600-03, RS4.569.600-08, RS4.569.600-11, RS4.569.600-16, K2 RPU-2 version 620 (six make and two break contacts) for a rated voltage of 12 V or PE-6 versions 2PR.309.023.923, 2PR.309.013.923, KZ - RES9 versions RS4.529.029-03, RS4.529.029-10, RS4.529.029-12, RS4.529.029-16, RS4.529.029- 19 or RES60 versions RS4.569.435-03, RS4.569.435-08.

The protective device is adjusted using an autotransformer or a suitable transformer having several secondary windings for different voltages. For example, a TAN2-127 / 220-50 transformer is suitable. By connecting the secondary windings to the primary in accordance with or in opposite directions, the necessary voltage values ​​\u255b\u180bof 3 and 255 V are set at the output of the transformer. Then, with a resistor R11 at a voltage of 180 V, and with a resistor RXNUMX at a voltage of XNUMX V, the device is turned off.

During installation and adjustment, care should be taken, since the device does not have galvanic isolation from the network.

Author: V.Aksenov, Penza

See other articles Section Protection of equipment from emergency operation of the network, uninterruptible power supplies.

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