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SCHEME OF NETWORK VOLTAGE STABILIZER FOR 3KW

This stabilizer, like ferro-resonance stabilizers, does not distort the shape of the voltage and is capable of operating without load. Its accuracy is somewhat lower, but it contains a power transformer of smaller dimensions, and there are no movable elements in the structure. Compared with ferroresonance stabilizers, this device has significantly smaller weight and dimensions.

The principle of the device is based on the inclusion in series with the load of one, two or three additional windings of the transformer when the mains voltage deviates from the norm. If the mains voltage is lower than the required one, the additional windings are switched in-phase with the network, and the voltage on the load becomes larger than the network voltage; If the mains voltage becomes higher than normal, the windings are switched on in phase with the mains voltage, resulting in a decrease in the voltage on the load. The role of such a transformer is performed by T1 , and additional windings by windings IV, V, VI .

On the integrated circuits DA3 - DA8, voltage comparators are made, which operate when the mains voltage deviates from the norm.

The circuit of the stabilizer of a network voltage on 3кВт

The reference voltages taken from the zener diode VD3 and the resistors R5 to R10 of the voltage divider are fed to the inverting inputs of the comparators. The non-inverting inputs of the comparators through the resistors R 11 through R 16 receive a voltage proportional to the network voltage and taken from the engine of trimmer R2 . The mains voltage sensor is the winding of the III transformer T1 , the voltage at which (approximately 10 V ) varies in proportion to the network voltage. It is straightened by a diode bridge VD2 . The pulsations are smoothed out by a C- shaped RC filter C4R1C5 . The time constant of the filter is chosen to be 1 ... 2 s , which excludes the comparators from triggering short-term surges.

Comparators DA3 - DA8 are configured to operate from mains voltage levels of 250 V, 240 V, 230 V, 210 V, 200 V and 190 V respectively. If the mains voltage exceeds these levels, then at the outputs (pin 9 ) of those comparators for which this condition is fulfilled, a high logic level voltage (logic 1 level) operates - about 12V . Thus, the difference in the operating levels of the comparators is 10 V , or about 5% of the mains voltage. The operating levels of the comparators DA5 and DA6 differ by 20 V. This corresponds to a control range of 220 V ± 5% . It should be noted that the state standards set the allowable mains voltage 220 V + 10% -15% (from 187 V to 242 V ). The same stabilizer, as seen, provides a higher accuracy of maintaining the value of the mains voltage.

All comparators are covered by positive feedback through resistors R17 to R22 . This is done to provide a small hysteresis (the difference between the operating voltages of each comparator when the mains voltage is increased and decreased). The value of the hysteresis is determined by the ratio of the resistances R17 and R11 for the DA3 chip and similar resistor pairs for the other comparators. These resistors are selected in such a way that the difference between the trip and release voltages of the comparators is 1.5 ... 2 V. If we exclude positive feedback, i.e. To make zero hysteresis, small fluctuations in mains voltage (caused, for example, by switching on and off of household appliances, and other noise) will lead to frequent operation of comparators and, correspondingly, increased wear of contacts of electromagnetic relays, as well as to additional interference in the network.

Thus, the accuracy of maintaining the voltage on the load is determined by the difference in the operating voltage of different comparators and the hysteresis value and is about 12V .

The operation of comparators and electromagnetic relays for different network voltages is illustrated in the table.

The circuit of the stabilizer of a network voltage on 3кВт

It can be seen from the table that when the mains voltage varies from 170 V to 270 V , i.е. By 23% , the voltage on the load varies from 200 V to 240 V, i.е. Only by 9% .

A few words about other circuit solutions of the stabilizer. The reference voltage for the inverting inputs of the comparators is supplied from the parametric stabilizer R4VD3 , which in turn is powered by an integrated voltage regulator made on the DA2 chip (output voltage +12 V ). The D818 series Zener diode has a very low temperature coefficient of voltage, which provides high accuracy of maintaining the reference voltage over a wide range of temperatures. This is also facilitated by feeding the parametric stabilizer from a stabilized voltage source. The supply of the windings of the relay K1 - K5 is carried out from the integral stabilizer +12 V (chip DA1 ). The need for a separate regulator to power the relay is caused by the fact that the mutual influence of the supply circuits of the comparators, the source of the reference voltage and the relay supply circuits should be eliminated as much as possible; Otherwise, triggering the relay and the resulting current change can lead to false trips of the comparators.

Voltage proportional to the mains voltage is removed from the separate winding of the transformer T1 (winding III). Although it could be removed from the winding of the II transformer. The need to use a separate winding is explained by the desire to exclude the effect of current changes. Caused by the operation of the relay, by the amount of voltage that is applied to the non-inverting inputs of the comparators from the transformer winding after rectification.

Logic of operation of comparators DAZ - DA8 and logic elements of DD1 chips . DD2 , and the work of electromagnetic relays K1 - K5 is visible from Table 4 and therefore does not need additional explanations.

In the device, you can use as a comparator, in addition to the circuits K1401CA1 (each of them contains four voltage comparators): integrated stabilizers KR142EN8B can be replaced by 15-volt (with the index "B" ). As diode bridges VD1. VD2 it is possible and to use devices of types КЦ402 - КЦ405. KC409. KC410. KC412 with any alphabetic indices. Diodes VD4 - VD7 , shunting windings of the relay. Can be of any type with an allowable reverse voltage of more than 15 V and direct current of more than 100 mA . Oxide capacitors - К50-16. K50-29 or K50-35 ; The rest is KM-6. K10-17. K73-17 . All the permanent resistors MLT, S2-23, C 1-12 ; Trim R2 and RIO are multi-turn SP5-2 or SP5-14 . Resistors R5 - R9 should have a permissible deviation of the resistances from the rated ones not worse than 1% ; If it is not possible to find resistors with this accuracy class, they should be selected from a group of resistors of the specified denomination using a digital ohmmeter. Relay K1 - K5 - foreign-made Bestar BS-902CS . The relays of this type terminal have a winding of 150 Ω , rated for 12 V operating voltage, and a contact group of a switching type. Designed for switching voltage 240 V at a current of 15 A. Switch Q1 - tumbler TV type 1-4 , in which all four pairs of contacts are connected in parallel. Transformer T1 is made on a magnetic circuit ШЛ50х40. The winding I is wound with a PEV-2 wire of 0.9 and contains 300 turns; Winding II - 21 turns of PEV-2 wire 0,45 ; Winding III - 14 turns of PEV-2 wire 0.45 : windings IV, V. VI contain 14 turns of PBD 2.64 wires. It is convenient to use a standard transformer of the OSM1-0.63 type. In which all the windings except the primary (it contains 300 turns) are removed, and the secondary windings are wound in accordance with the data given above. When manufacturing the transformer, the same conclusions of the windings I, IV, V, VI should be marked (in the diagram they are indicated by dots). The rated power of such a transformer is 630 watts .

All elements of the voltage regulator, except for the transformer T1 and toggle switch Q1, are mounted on a board made of fiberglass. In the author's copy the installation is made with wires, although it is possible to develop a printed circuit board. The microcircuits DA1 and DA2 are installed on radiators with an area of ​​about 100 cm2 and 30 cm2 respectively

Adjustment of the stabilizer consists in setting the value of the nominal voltage on the load equal to 220 V , and in the selection of the thresholds of operation of the comparators DA3-DA8 equal to 250 V, 240 V 230 V, 210 V, 200 V and 190 V respectively. To configure, you need two voltmeters, measuring AC voltage in the range of 300 V, and a laboratory autotransformer, the output voltage of which can be changed from 170 V to 270 V. To indicate the states of comparators, it is desirable to connect to each of them a series-connected resistor of resistance 10 ... 15 KOhm and LED series AL307 so that the anodes of the diodes are connected to the outputs of the 9 microcircuits of the comparators. And the free leads of the resistors - with the common wire (ie, as it is done in the simplest logical probe in Figure 8 of this book). Of course, you can do with a DC voltmeter. With which to measure the voltage at the outputs of comparators, but this is less convenient. To the output of the laboratory autotransformer, connect the voltage regulator and the first voltmeter; The second voltmeter is connected to the load sockets of the stabilizer. The engines of the trimmer resistors R2 and R 10 are set to the rightmost position according to the scheme, and the voltage of the autotransformer is set at 190 V. At the same time, the outputs of all comparators should have a low logic level (the LEDs do not glow, and when determining the voltage level with a DC voltmeter, it should show no more than 1 V. By moving the trimmer R2 driver, the comparator DA8 triggers the output of the high logic Level (about 10 ... 12 V. ) Then, smoothly increasing the autotransformer voltage to 250 V , the DA3 comparator triggers, while the sequential operation of the comparators DA7 , DA6, DA5, DA4 is observed by the LEDs lighting. Are selected by adjusting trimmer R10 . After setting the operating limits of the comparators DA8 and DA3, check the thresholds of the other comparators, which must be equal to the values ​​indicated above, if necessary, the entire setting can be repeated.

A load of up to 3 kW can be connected to the voltage regulator. If the accuracy of maintaining the output voltage can be lower than specified, the number of secondary windings of the transformer T2 can be reduced to two, and their voltage increase from 10 V to 15 V. Thus, accordingly, the number of comparators decreases, and the thresholds of their operation should be set according to the voltages of the secondary windings T2 .

It should be said about the possibility of using semiconductor switches for switching secondary windings of the transformer T1 in order to replace the contacts of the electromagnetic relays K1-K5 . Indeed, the contacts of electromagnetic relays have a limited lifespan, caused by their wear, which is the greater, the greater the number of trips and the more switching currents. In this sense, the use of semiconductor elements is preferable. In this case, you can apply triacs. However, it should be noted that one group of relay switching contacts can be replaced by two triacs, i.e. This device requires 10 triacs. In addition, it will be necessary to take special measures so that the triacs of one group of contacts are not simultaneously in the open state - this will be the closure of the secondary winding of the transformer T2 and the failure of the triacs. This situation is due to the fact that after tripping the voltage from the control electrode, the triac can not close before the end of the half-period of the mains voltage, which is 10 ms . At the same time, another triac from this pair will open almost immediately after the control voltage is applied to the control electrode, which can occur at any time during the half-cycle. To exclude the simultaneous open state of two triacs, special measures should be taken - for example, to supply and remove voltages from the triac control electrodes only at the beginning of the half-cycle. This will significantly complicate the control scheme. In addition, such a switching algorithm will not eliminate completely through currents, since triacs commute an inductive load (transformer) capable of accumulating electromagnetic energy. Consequently, to completely eliminate the through currents, the triac control algorithm must be even more complicated. Most likely, the shape of the mains voltage will be significantly distorted during key switching times.

In view of the foregoing, the designer should decide whether to prefer using electromagnetic relays or triacs. Author's copy of the stabilizer, performed according to the above scheme, reliably works for more than 1 year and feeds the load with a power of up to 3 kW.