SU1647763A1 - Device for controlling power of three-phase capacitor bank - Google Patents

Abstract

The invention relates to electrical engineering and can be used to control the power of a three-phase capacitor bank by switching triangle-star capacitors. The purpose of the invention is to increase reliability and speed. The invention allows the forced discharge of power capacitors to certain residual voltages. As a result, the duration of capacitor switching from a triangle to a star and current surges when a star is switched on are reduced. When the control unit sends a command to switch from a triangle to a star, the thyristor switch is turned off, the logic unit generates commands to turn on the thyristor switches. Capacitors are discharged to certain voltages given by the pre-active elements. Threshold elements form commands to turn off the thyristor switches and stop the discharge of capacitors. Then, at the moment of the equality of the residual voltage values on the capacitors of the corresponding instantaneous voltage of the power supply network, the star switch is turned on. 2 Il.

Description

The invention relates to electrical engineering and can be used to control the power of a three-phase capacitor bank by switching from a triangle to a star.

The purpose of the invention is to increase reliability and speed,

Fig, 1 shows a block diagram of the proposed device; Fig. 2 shows voltage curves on capacitors explaining the operation of the device.

The device (Fig. 1) contains a thyristor switch 1 for switching on a capacitor 2-4 of a capacitor battery with a star and a thyristor switch 5 for switching on capacitors 2-4 of a capacitor battery with a triangle.

Depending on the control parameter X, the control unit 6 issues commands to turn on or off switches 1 and 5. Parallel to capacitors 2-4, through thyristor switches 7-9, executed on lockable thyristors 10-12, bypassing the outputs of diode bridges 13-15, are turned on discharge resistances 16-18. Logic block 19 consists of six elements And 20-25 and three threshold elements 26-28. The first inputs Xi of the elements AND 20-22 are connected to the first output U1 of the control unit 6 and the direct input

ABOUT

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BANCH element 29, the output of which is connected to the input of the switch 1 by switching on a capacitor battery by a star. The second diodes Xa of the elements AND 20-22 are connected to the inverse of the input of the BANCH 29 element and the output of the RS flip-flop 30, the S-input of the RS flip-flop 30 is connected to the second output UA of the control unit 6 and the input of the capacitor bank switching switch 5 by a triangle. The inputs of the threshold elements 26-28 are connected to the outputs of the voltage control elements 31-33 connected in parallel with capacitors 2-4, respectively. The outputs of the threshold elements 26-28 are connected to the second inputs of Hz elements And 23-25, the first inputs Xi of which are connected to the outputs of the elements And 20-22. The output of the element And 34 is connected to the R-input of the RS-flip-flop 30, and the inputs - the outputs of the threshold elements 26-28. The outputs of the elements 20-25 are connected to the inputs of the formers 35-37 pulses, the outputs of which are connected to the control inputs of lockable thyristors 10-12. The shapers 35-37 of control pulses consist of shapers (keys) 38-40 of turn-on thyristors 10-12 and shapers (keys) 41-43 of turn-off pulses of these thyristors.

The device works as follows.

Depending on the value of the monitored parameter X, a signal appears at one of the outputs of control unit 6.

Suppose that a control signal (Log, 1) appears at the second output UA of control unit 6, allowing switching on switch 5. The semiconductor switches of switch 5 are turned on, the capacitors 2-4 of the network are connected in a triangle pattern. The voltage on each capacitor 2-4 becomes equal to the linear voltage of the supply network (UV - phase voltage of the supply network). At the outputs of the voltage control elements 31-33, signals equal to a pf appear (a is the proportionality coefficient) that are fed to the inputs of the threshold elements 26-28. As a result, the outputs of the threshold elements 26-28 appear as Log.O .

At the same time, the signal Log.1 from the output U2 of the control unit 6 is supplied to the S input of the RS flip-flop 30 and translates it into another steady state with the signal Log.1 at the output, which is fed to the inverse input of the BAN 29 element.

In the case when the monitored parameter Xi changes so much that a capacitor battery needs to be switched from the triangle to the star circuit, a log (0-15) appears on both outputs of the control unit for a short time (10-15 ms)

(time to figure 2). The switch thyristor 5 closes at the moments when the current passes through them to zero (moments ti, 12, gz, fig.2). The appearance at a subsequent time (time t4, figure 2) of the control signal

Log.1 on the first Ut of the output of control unit 6 does not turn on switch 1 by the star, since Log.1 is stored at the inverse input of BAN 29. At this point in time at the exits

elements And 20-22 appear Log.1, which are fed to the inputs of the formers 38-40 turn-on pulses, forming pulses (positive polarity) at the control inputs of lockable thyristors 10-12. Thyristor switches 7-9 open, close capacitors 2-4 to discharge resistances 16-18, respectively. The voltage on the discharged capacitors decreases rapidly,

accordingly, the voltages at the inputs of the threshold elements 26-28 decrease.

The voltage triggered threshold elements selected one a aa, and the other two a if / 2, Let the threshold element 26

triggered when the residual voltage on the capacitor 2 is equal to, and the threshold elements 27-28 - when the residual voltage on the capacitor 3 and 4 is equal to 1-2 (V; jf UV). When the voltage decreases

on capacitor 2 to / 2, Log.1 appears at the output of the threshold element 26, which is fed to the input Xi of the element 34 and through the element 24 to the input of the generator 41, 42 of the impulses to turn off the generated pulse (negative polarity at the control input lockable thyristor 10). which leads to the closing of the switch 10, the termination of the discharge of the capacitor 2 (time ts, figure 2).

Similarly, the switches 8 and 9 close when the residual voltage on the capacitors 3 and 4 decreases to 2/2 Uf (time te. Fig. 2) Simultaneously with the arrival of Log.1 to the inputs X2 and Xs of the element

And 34 Log1 appears at its output, which (through a differential circuit) is fed to the R input of the RS flip-flop 30. The trigger 30 is transferred to another steady state with the Log signal. O at the output, which is fed to the inverse input of the element BAN 29, by enabling the star switch on switch 1 to turn on the capacitor battery. Switch 1 is turned on at the time of zero voltage difference on

its switch, carried out an unstressed connection of capacitors 2-4 to the system of phase voltages of the power supply network (moment t, figure 2).

Claims (1)

Thus, the proposed circuit allows the forced discharge of power capacitors to certain residual voltages. As a result, the duration of capacitor switching from a triangle to a star is reduced, current surges when capacitors are turned on are reduced, electric power losses are reduced, and the quality of the supply mains voltage is improved. All this increases the reliability of the capacitor installation, as well as the galvanically connected electrical equipment. Switches in bit circuits can also be made on bipolar interconnected lockable thyristors. The invention is a device for controlling the power of a three-phase capacitor battery by switching from a star to a triangle, containing a star switch for switching a capacitor battery and a triangle switching switch for a capacitor battery, a control unit with inputs for connecting to an adjustable parameter sensor and with switching on and switching three Single resistances connected in series with three switches made on lockable thyristors, elements AND, RS-trigger, characterized by In order to increase reliability and speed, it is equipped with a BAN, three impulse drivers, three capacitor voltage controls, a three-input AND element and a logic unit made of six AND elements and three threshold elements, the output Switched control unit is connected to the first inputs the first three elements of the logical block and the direct input of the BANGE element, the output of which is connected to the input of the switch switch on the capacitor battery by a star, the second inputs of the first three elements The ECU unit is connected to the inverse input of the BANNER element and the RS output of the trigger, the R input of which is connected to the output Turn on the control unit and the input of the capacitor battery switching switch by a triangle, the inputs of the threshold elements are connected to the outputs of the corresponding capacitor voltage control elements, and the outputs are connected to the first the inputs of the three second elements And the logical unit, the second inputs of which are connected to the outputs of the first three elements And, the output of the three-input element And is connected to the S-input of the RS flip-flop, and its inputs - from the output Dami threshold elements, the outputs of each of the three first and each of the three second elements And are connected in pairs to the inputs of the corresponding pulse shapers, the outputs of which are connected to the control inputs of the corresponding lockable thyristors.  "L, 1 / 4b Yu it h t5 FIG. 2   "S,