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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Electricity consumer protection device. 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 Unacceptable changes in the mains voltage in a significant range from the nominal value lead to the failure of household appliances. So, reducing the voltage below the norm for the refrigerator is fraught with the fact that the engine may not have enough starting torque and its winding will burn out. An increase in voltage leads to an increase in the current flowing through the load, which will also lead to its failure. A neutral break at a substation can increase the mains voltage to a huge voltage of 380 V, which no household appliance can withstand. The proposed device allows you to protect household appliances from abnormal changes in mains voltage. The device is operable in the voltage range from 20 to 440 V. The permissible current is about 16 A, it depends mainly on the relay used. The microcontroller, which is part of the device, monitors the mains voltage and, if it changes by more than 15%, disconnects the load and signals with LEDs. The limit of 15% is chosen based not on GOST standards, but on the basis of real mains voltage fluctuations, and can easily be corrected by changing several program cells. Three designs have been developed. The first two are assembled according to the scheme shown in Fig.1. The device, the appearance of which is shown in Fig. 2, a, is designed to be built into a double socket; fig. 2, b - for hanging on an apartment machine. The third device (Fig. 3) was supplemented with a network filter and varistors that protect the structure, and at the same time consumers from impulse noise. The principle of operation of the device, the diagram of which is shown in Fig.1. The mains voltage is supplied to input X1, rectified and limited to 15 V by the C2R4VD1-VD3 circuit, then stabilized by the D2 chip. It powers the microcontroller. After some delay, the internal oscillator of the D1 chip is started and the program starts to run.
The voltage taken from the R1R2 divider is fed to the GP1 input, which is configured as an analog comparator input. The input voltage is monitored: if it is in the zone of 15% of the nominal value, then the relay K1 and the LED HL1 "Norm" turn on; if the voltage at any time exceeds 253 V, the controller will turn off the relay and turn on the HL2 LED in flashing mode. After 45 seconds, the controller will check the mains voltage again and, if it is normal, will turn on the relay again. The same thing will happen if the voltage drops and is less than 187 V, with the only difference that the HL3 LED will flash. In this case, the measurement of the minimum voltage is made 5 ms after the mains voltage passes through zero, that is, at the maximum of the sinusoid. Capacitor C1, together with resistors R1, R2, is a low-frequency filter that prevents the comparator from triggering as a result of impulse noise. If it is not installed, the device will operate from a short-term voltage drop, for example, as a result of turning on the refrigerator engine. It should be noted that the response time of the protection depends mainly on the speed of the applied relay and the value of the capacitor C1.
In the third design (Fig. 3), a line filter is added on the elements L1, L2, C1-C3, R1, R2, and at the same time a monitoring circuit is organized for the health of the varistors on the elements VD1, VD2, R3, R4, since large impulse surges they may fail. In case of failure of the varistors, the HL2 LED will blink.
Details shown in Fig.3. As D2, you can use the 78L05 chip. Capacitors C1-C3 type K78-2, C5 type K73-17 for a voltage of 500 ... 600 V, C7-C8 type K50-35, the rest - KM. Diode VD5 can be replaced by D815D. The VD5 diode is designed for a voltage of 500 ... 600 V, the remaining diodes - for a voltage of 25 ... 50 V and a current of 100 ... 300 mA. MLT type resistors. Arrester U1 with a breakdown voltage of 1 kV. Varistors 561KD14 can be replaced by any with an absorption energy of 50 ... 200 J. Choke L1 is wound on a core from a magnetic antenna with a diameter of 8 and a length of 20 mm with a wire with a diameter of 1,5 mm and contains 20 turns. Inductor L2 is located on an alsifer ring with a diameter of 50 ... 60 mm and contains 15-20 turns of wire 1,5 mm in diameter, folded in half. The design shown in Fig. 2b is made using the surface mount method - an imported zener diode for a voltage of 12 ... 15 V and a power of 1,3 W is installed there. A microcontroller in a SOIC package is used. Ceramic resistors and capacitors sizes 0603, 0805 and 1206. Both PIC12.675 and PIC12.629 microcontrollers can be used in all designs. In the first case, the microprogram shown in Table 1 is written, in the second - in Table 2. Table 1 :020000040000FA
Table 2 :020000040000FA
Establishing the device is reduced to the selection of the resistor R1 (Fig. 1) or R5 (Fig. 3). X1 is connected to the LATRA output, on which a voltage of 253 V is set and, by increasing the resistance R1 (R5), the HL2 (HL3) LED is turned on. Zone 187 B will be set automatically. If it is necessary to shift the upper trigger zone, for example, to 240 V, then the lower one will change to 174 V. Attention! During commissioning, care must be taken not to accidentally break the resistor R1 (R5), since the microcontroller can fail, despite the fact that it has protective diodes inside. All designs are made on printed circuit boards made of one-sided fiberglass with a thickness of 1,5 ... 2 mm. Figure 4 shows a 56x90mm printed circuit board for a double socket; in Fig. 5 - a printed circuit board with dimensions of 15,5x65 mm for connection to an apartment machine; in Fig. 6 - a diagram of a device with dimensions of 78x200 mm with a filter.
Author: S.M. Abramov
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