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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Relay voltage control device in the mains. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies Today, in amateur radio literature and on the Internet, you can find many descriptions of home-made devices that monitor the voltage in the electrical network and turn off electrical appliances powered by it if the voltage goes beyond the permissible limits for them. As a rule, microcontrollers, operational amplifiers and other modern high-tech electronic components are used in these devices. But until quite recently, this problem was successfully solved by simpler means. For example, using electromagnetic relays. One of these "retro" constructions is described by the author in the proposed article. Despite the fact that the standards (for example, [1]) establish rather strict standards for voltage stability in household electrical networks, for various reasons it quite often goes beyond the permissible limits. This poses a danger to household electrical appliances, of which there are a lot in any apartment or residential building today. Especially for those that are connected to the network almost constantly. It helps here only the presence of an automatic device that continuously monitors the voltage and disconnects all consumers from the network in the event of a dangerous increase or decrease. When I had a need for such an automaton, those of them, the descriptions of which I managed to find for self-production (for example, [2]), seemed to me too complicated. I decided to design and make my own. Its scheme is shown in Fig. 1. At a voltage below 198 V (220 V-10%), it turns off the electrical network of the apartment, and when it returns to normal, it turns it on again. If the value of 242 V (220 V + 10%) is exceeded, the network also turns off, but its work is not restored until the owner of the apartment, having made sure that the voltage is normal from the PV1 voltmeter, presses the button SB1 "Start" . This move away from full automation is better for safety and is quite acceptable, since overvoltages are rare. For three years of continuous operation of the machine, there were many shutdowns for undervoltage, but only eight times for overvoltage. They occurred mainly at night, sometimes during thunderstorms.
As can be seen from the diagram, two step-down transformers T1 and T2 are connected in series along the primary and secondary windings, so they can easily withstand the increase in mains voltage to 380 V or more, which happens when the neutral of the three-phase network breaks. The rectifier for powering relay K3, whose contacts K3.1, withstanding current up to 20 A, connect consumers to the network and disconnect them from it, is made according to a bridge circuit on VD4-VD8 diodes and is powered by series-connected windings of III transformers with a total rated voltage of 20 B. The presence of voltage at the output of this rectifier, and therefore in the supply network, is signaled by the HL1 LED. The rectifier for controlling the voltage value is assembled on diodes VD1 - VD4 also in a bridge circuit. It is powered by series-connected windings of II transformers (their total nominal voltage is 12,6 V). The peculiarity of this rectifier is that its smoothing capacitor C1 has a relatively small capacitance so that voltage changes can be tracked without delay. When the voltage in the network is greater than the lower threshold, a voltage is applied to the circuit of the HL3 LED - Zener diode VD11 - the winding of the polarized relay K1, which exceeds the sum of the direct voltage drop across the LED, the stabilization voltage of the Zener diode and the relay operation voltage. Contacts I and L of relay K1 are closed. If at this time contacts I and R of relay K2 are also closed, then relay K3 is activated, connecting consumers to the network. By adjusting the tuning resistor R9, it is ensured that when the voltage in the network drops below the permissible 198 V, the voltage at the zener diode VD11 becomes less than its stabilization voltage and it closes, stopping the current through the relay winding K1. As a result, the contacts I and L of this relay open the circuit of the relay winding K3. It disconnects consumers from the network until the voltage in it returns to normal. The overvoltage control channel is built in a similar way, but the VD12 zener diode serves as the threshold element in it, the operation threshold (242 V) is set by the trimming resistor R11, and when it is exceeded, the K2 relay contacts open the K3 relay winding circuit and turn on the HL2 LED. As relay K2, a bi-stable polarized relay RP4 was used, which differs in that its contacts do not independently return to their original position when the voltage is removed from the windings. In order to transfer the relay armature in one direction or another, it is necessary to apply a voltage pulse of the corresponding polarity to one of the windings. Therefore, to return the relay K2 to its original state after operation, the device has a button SB1, which is pressed to reconnect to the network consumers of electricity, disconnected due to excess voltage. Sometimes you have to press this button to bring the device into working condition after connecting to the network, since the initial position of the K2 relay contacts is unknown and can be anything. Zener diodes VD9 and VD10 limit the voltage supplied to the relay windings K1 and K2 after they are triggered, which prevents the current in these windings from exceeding the allowable values. The author used in the design two unified power transformers TPP261-127/220-50 with armored magnetic cores [3]. The primary windings of these transformers are used as windings I (pins 2 and 9 with a jumper between pins 3 and 7). To form the windings II, jumpers are installed between the terminals 12 and 19 of the transformers, and the voltage is removed from the terminals 11 and 20. The terminals of the winding III are 15 and 16. Instead of two transformers T1 and T2, it is possible to use one that can withstand a primary voltage of up to 380 V. It can be wound independently on the SHL20x40 magnetic circuit. Winding I should have 2700 turns of PEV-2 wire with a diameter of 0,21 mm, winding II - 155 turns of PEV-2 wire with a diameter of 0,35 mm, and winding III - 254 turns of the same wire. With a primary voltage of 220 V, the voltages on the windings II and III should be 12,6 and 20 V, respectively. Relay K1 is a two-position single-stable polarized relay RP7 with a predominance of the right contact (version RS4.521.005). To obtain a winding with a resistance of about 600 ohms, its windings II (470 ohms) and III (140 ohms) are connected in series, for which a jumper is installed between terminals 4 and 6 of the relay block. You can use a relay of the same type, versions RS4.521.019 with a winding resistance of 480 Ohm or RS4.521.012 with a winding resistance of 700 Ohm. Relay K2 is a two-position bi-stable polarized relay RP4 (version RS4.520.004). Its windings 1-IV with a resistance of 130 ohms are connected in series, for which jumpers are installed between contacts 2-3, 4-8 and 6-7 of the relay block. Winding VII with a resistance of 2250 ohms is also used. It is possible to use relays of versions RS4.520.011 with windings with a resistance of 460 and 2700 Ohm or RS4.520.012 with windings with a resistance of 500 and 830 Ohm. Reference data for polarized relays RP4 and RP7 can be found in [4]. When selecting replacements, it should be borne in mind that the windings of polarized relays of different designs can be brought to different contacts of their pads. Winding resistance spread of identical relays can reach ±15...20%. In the absence of the required relay RP7, instead of it, you can use a relay RP4 that is suitable for the resistance of the windings. These relays are structurally the same, but differ in the adjustment of the contacts. It is necessary to remove the protective aluminum casing from the RP4 relay, unscrew the fixing screw of the left contact by one or two turns, manually transfer the armature to this contact, then slowly turn the adjusting screw of the left contact until the armature independently transfers to the right. In this position, the left contact should be fixed, and then put on the casing on the relay. Relay K3 - RKS3 (version RS4.501.200) with a winding with a resistance of 175 Ohm and a rated operating voltage of 24 V [5]. It can be replaced by another relay with the same operating voltage of the winding, the contacts of which are capable of switching a current of at least 20 A. Voltmeter PA1 - Ts4209 detector system with a measurement limit of 500 V AC voltage. The machine is assembled in a metal case measuring 230x160x80 mm, which must be grounded. Relay K3 is placed in a separate compartment of the housing due to the fact that its contacts connected to the mains are not protected from accidental contact. Zener diodes VD9 and VD10 are equipped with heat sinks with an area of 50 cm2. The power consumed by the machine from the network is about 7 watts. When setting up the machine, the mains voltage is supplied to it through a laboratory adjustable autotransformer and the lower and upper thresholds are set with trimmers R9 and R11, respectively. If desired, an audible signaling device can be connected to sockets XS1 and XS2, which will sound an alarm when the permissible voltage in the network is exceeded. A possible signaling device circuit is shown in fig. 2. At its input there is a diode bridge VD1-VD4, which eliminates the need to observe polarity by connecting the XP1 and XP2 plugs to the sockets of the machine. On transistors VT1 and VT2, a conventional multivibrator is assembled, generating pulses with a frequency of about 800 Hz. Transistor VT3 - power amplifier of the signal supplied to the telephone capsule HA1. Transistor VT3 and zener diode VD5 should be installed on heat sinks with an area of 50 cm2.
Literature
Author: S. Babyn
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