RU19940U1 - DEVICE FOR NON-CONTACT COMMUTATION OF A THREE-PHASE CAPACITOR BATTERY - Google Patents

Description

Device for contactless switching a three-phase capacitor bank

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The invention otoyteya to the field of electrical engineering and can be used in those sectors of the economy where it is necessary to ensure lack of care and high-speed non-switching, free of electromagnetic noise, capacitor banks in three-phase AC networks, in particular, reactive power compensation units.

A device for regulating reactive power that implements the known method in electric networks by switching a three-phase capacitor bank by turning it on and off alternately, moreover, the connection is made when the difference between the respective line voltages of the network and the battery is zero, and the battery is disconnected from one of the phases network at a time when the current in this phase is zero. Then, the battery is disconnected from the other two phases at the moment of equal current in these phases to zero, and switching on is carried out in the reverse sequence (see. S. USSR No. 811400 M. class. I02) 3/18). The specified device provides high-speed switching of a capacitor bank without current surges. However, it requires means to determine the moment when the difference between the respective line voltages of the network and the battery is zero, which leads to the need to install zero voltage sensors in the main circuit, which complicate and cost the capacitor installation.

A device for contactless switching a three-phase capacitor bank is also known, which implements the known method and contains a three-phase capacitor bank with an internal phase connection in a triangle connected to a three-phase AC network via semiconductor (thyristor-diode) switches, and a control system including a three-phase synchronizing transformer connected to the network, three comparators, pulse transformers, control command generator, three synchronous triggers, high-precision generator -frequency pulses, logic elements, the pulse amplifiers. In this case, the installation inputs of the second and third triggers are connected to the non-inverting output of the first trigger, one of the inputs of the logic elements is connected to the output of the corresponding synchronous triggers, and their second input is connected to the output of the high-frequency pulse generator, the outputs of all logic elements are connected to the inputs of the corresponding pulse amplifiers, outputs which, in turn, are connected via pulsed transformers to the control circuits of the thyristors of semiconductor switches (see a.s. USSR No. 1099314 M. class G05f 1 / 70). This device in its technical essence is the closest to the claimed and taken as a prototype. It does not require funds to determine the moment of natural switching of thyristors, but is based on a standard organization

control pulses when turned on, taking into account the situation that occurred when the battery was turned off.

The disadvantage of this device is that it involves the installation of thyristor-diode switches in each line and cannot be used for the main current circuit with counter-parallel thyristors in two lines and one line connected directly to the network, which is simpler and more economical, so as contains fewer semiconductor power devices. In addition, the maximum value of the repeated voltage across the thyristors in circuits with thyristor-diode switches when the battery is disconnected reaches 2.4 amplitude values of the line voltage of the network, i.e. 1270 volts in industrial installations (with a rated voltage of 380 volts). This reduces the operational safety and reliability of these installations.

The technical problem to which the claimed device is directed is to eliminate these shortcomings, i.e. simplification of the switching device and increase its reliability.

The specified technical problem is achieved by the fact that in the known device for contactless switching of a three-phase capacitor bank, it contains a three-phase capacitor bank with an internal phase connection in a triangle connected to a three-phase AC network via semiconductor switches, and a control system including a three-phase synchronization transformer connected to the network, three comparators, pulse transformers, control command generator, synchronous triggers, high-frequency generator pulses, logic elements, amplifiers of impulses, while the installation inputs of the second and third triggers are not connected to the non-inverting output of the nerve trigger, one of the inputs of the logic elements is connected to the output of the corresponding trigger, and the second inputs of all logic elements are connected to the output of the high-frequency pulse generator, the outputs of all logic elements are connected to the inputs of the respective pulse amplifiers, the outputs of which, in turn, are connected via pulse transformers to the control circuits tori semiconductor switches, in contrast, the claimed comprises an additional fourth synchronous trigger, semiconductor switches are in the form of two pairs of antiparallel-connected thyristors included in the two line wires phases A and C of the capacitor bank, one of the pulse transformers is made into a three-winding performance. In this case, the secondary windings of the phases c and in the synchronizing transformer are connected respectively to the inverting and non-inverting inputs of the first comparator, and the phase winding of the same transformer is connected to the inverting input of the second comparator and the non-inverting input of the third comparator, in which other inputs are connected to the housing bus. The synchronizing inputs of the second and fourth triggers are connected together and connected to the output of the third comparator, and the same inputs of the first and third triggers are connected respectively to the outputs of the second and first comparators. The information inputs of all triggers are connected to

the positive pole of the power source. The installation input of the fourth trigger is connected to the output of the control command generator, and the same input of the first trigger is connected to the inverting output of the fourth trigger. Moreover, the outputs of the first and third pulse amplifiers are connected through two-winding pulse transformers, respectively, to the control circuits of the direct thyristor phase C and the reverse thyristor phase A semiconductor switch, and the output of the second pulse amplifier is connected through the aforementioned three-winding pulse transformer, respectively, to the control circuits of two other thyristors of the same first and a second pair of thyristors of a semiconductor switch.

As the analysis of transients during disconnection of the capacitor bank from the network using thyristors shows, after disconnecting, the residual voltages on the capacitors are distributed so that one of the linear voltages of the capacitor bank is equal to the amplitude value of the line voltage of the network, the other is less than this value, and the third exceeds the voltage amplitude network. The maximum value on switching thyristors after disconnecting the battery is determined by the sum of the amplitude value of the line voltage of the network and the same residual voltage of the battery.

It follows that in the main current circuits with counter-parallel connected thyristors in two linear wires and one line connected directly, the maximum value of the repetitive voltage across the thyristors (the same as in the prototype) will occur if

the maximum residual voltage on the phases of the battery after disconnection will be connected between the line connected directly to the network and any other line; if the greater of the residual voltage of the battery after shutdown is applied between two lines connected to the network via thyristors, then the maximum value of the repeating voltage on the thyristors will not exceed the double amplitude value of the network voltage, i.e. 1.2 times less than in the prototype.

Such a distribution of the battery residual voltages, as in the latter case, is ensured by the proposed device, namely, that the moment of termination of the supply of control pulses is in the interval from the moment the linear voltage passes through zero between the line connected directly to the network and the line preceding it in order phase rotation, and until a similar transition through zero of the next line voltage.

Thus, the increase in reliability and safety in circuits with counter-parallel thyristors in two lines and one line connected directly to the network is ensured by reducing the maximum value of the repetitive voltage across the thyristors due to the optimal voltage distribution of the capacitor bank, which is achieved by choosing the moment of stopping the supply of control pulses on thyristors.

In addition, a decrease in the indicated voltage values allows the use of thyristors of lower voltage classes for battery switching, which in turn reduces the cost of switching devices and the capacitor unit as a whole.

At a high switching frequency of the battery (for example, in the case of compensation for rapidly changing reactive loads), before the next battery is turned on, it does not have time to discharge any noticeably in the previous shutdown cycle. To ensure that a non-discharged capacitor bank can be connected to the network without bursts of the charging current, the sequence of control pulses is fed primarily to a thyristor connected counter-parallel to the thyristor that conducts current last when the battery was disconnected from the network before. Thus, in the main current circuits with thyristors, counter-parallel connected in two lines, and with one line connected directly to the network, the same speed is ensured as in the known device.

From the above it follows that the claimed device allows you to realize the advantages inherent in the known device (speed, simplicity and reliability of control circuits) in circuits with opposite parallel thyristors in two lines and one line connected directly to the network, which are simpler and more economical, since they contain less number of power semiconductor devices. In addition, the claimed device allows in these schemes to achieve an increase of-7-2ё // (g

reliability and safety and an additional reduction in the cost of the capacitor unit by reducing the maximum voltage value on the thyristors but in relation to the prototype. A one third reduction in the number of semiconductor devices reduces by 33% the loss of their heating, and, consequently, the temperature of the medium inside the installation. It also increases the reliability of the electronic control system. Due to the reduction of losses, the efficiency of the capacitor unit increases.

In FIG. 1 is a diagram of a capacitor bank with opposing parallel thyristors in two lines and one line connected directly to the network, as well as a control circuit that implements new communications; in FIG. 2 - time diagrams of voltages and currents operating in the circuit when the non-discharged battery is turned off and then turned on; in FIG. 3 - time diagrams of currents and voltages when a discharged battery is turned on.

The circuit contains a three-phase capacitor bank 1 with an internal phase connection in a triangle connected to a three-phase AC network 2 through anti-parallel connected thyristors 3.4 and 5.6 in two lines (A and C); three-phase synchronizing transformer 7 connected to the network; comparators 8-10; pulse transformers 11-13; shaper management teams 14; synchronous triggers 15-18; logical elements 19-21; pulse amplifiers 22-24; high frequency pulse generator 25.

g / 2 The inputs of the comparators 8-10 are connected to the phases of the secondary winding of the synchronizing transformer 7. The synchronizing inputs (C) of the triggers 16 and 18 are connected directly to the outputs of the comparators 9 and 8, and the same inputs of the triggers 15 and 17 are connected together and connected to the output of the comparator 10 The information inputs (D) of triggers 15-18 are connected to the positive pole of the power source. The installation input (R) of the trigger 15 is connected to the output of the control command generator 14, the same input of the trigger 16 is connected to the inverting output of the trigger 15, and the installation inputs of the triggers 17 and 18 are connected to the output of the trigger 16. One of the inputs of the logic elements 19-21 is connected to the output of the corresponding trigger, and the second input to the output of the 25 pulse generator. The outputs of the logic elements 19-21 are connected to the inputs of the pulse amplifiers 22-24, the outputs of which, in turn, are connected via thyristor isolation transformers 11-13 to the control circuits of the thyristors. Moreover, the outputs of amplifiers 22 and 24 are connected through two-winding transformers to thyristors 5 and 4, respectively, and the output of amplifier 23 is connected through three-winding transformer to thyristors 3 and 6. Phase voltage of the network through a transformer 7 goes to the inputs of comparators 8-10, which change the logical state of the output when the voltage applied to the inputs of the corresponding comparator passes through a zero value, thereby forming rectangular pulses with a frequency of the mains voltage. The leading edge of the pulses of the comparator 8 coincides with the moment of the transition through zero of the linear voltage of the UBC network from the region

false to the area of negative values. The leading edges of the pulses of the comparators 9 and 10 coincide with the moment of transition through zero of the phase voltage of the network UA. Moreover, for the comparator 9 - in the direction of negative, and for the comparator 10 - in the direction of positive values. Synchronous triggers 15-18 are switched on the leading edge of the signal at the clock input, resetting the triggers to the initial state is carried out by a zero signal at the installation input.

The device operates as follows. At the point in time preceding the start of battery shutdown, from the output of the driver 14 to the installation input of the trigger 15 receives a zero signal, causing a single signal at its inverting output. From the outputs of the triggers 16-18 to the inputs of the logic elements 19-21, performing the And function, single signals are received, therefore, the high-frequency pulses of the generator 25 pass through these elements to the inputs of the amplifiers 22-24 and then through the transformers 11-13 to the control circuits of thyristors 3- 6, keeping the latter open.

When the battery is turned off, the supply of control pulses is stopped at the moment when the phase A voltage of the network goes through zero to the side of positive values, which, in accordance with the claimed connections, is in the interval from the moment when the line voltage UAB passes through zero (voltage between line B connected to the network directly and the line A) preceding it in the order of phase rotation until the same transition of the linear voltage UBC– This is carried out as follows. Suppose that at time ti (Fig. 2) a command is sent to turn off the battery, i.e. at the output of the shaper 14 is set to a single signal. Since the trigger 15 is no longer held in its original state, it will switch over and the zero signal to its uniform front of the first impulse from the output of the comparator 10 (moment ti in Fig. 2, corresponding to the transition through zero towards the positive values of the voltage of the phase A network) the inverting output, arriving at the installation input of the trigger 16, sets the zero signal at its output, which in turn sets the triggers 17 and 18 to zero. The zero signals from the outputs of the triggers 16-18, coming to the inputs of the logic elements 19-21, block the passage of the control pulses of the generator 25 to the amplifiers 22-24 and further to the thyristors. Thus, the cessation of the supply of control pulses occurs at the moment when the voltage of phase A of the network does not go through zero towards positive values.

After stopping the supply of control pulses in the circuit, the following processes occur. At time ts, when the current in line A becomes zero, thyristor 3 closes, thyristor 4 does not open due to the absence of control pulses, and line A is disconnected from the network. After another quarter of the alternating current period (time t4 in Fig. 2), the current in line C becomes zero, thyristor 6 closes, and the battery is completely disconnected from the network. Obviously, with such synchronization of the moment of stopping the supply of control pulses, thyristor 6 will always be the last to conduct the current after disconnecting the battery. As can be seen from the diagram in FIG. 2, the maximum voltage value on the thyristors of line C does not exceed the double amplitude of the mains voltage. The voltage on the thyristors of line A is even less.

In the proposed embodiment of the implementation of new connections, thyristor 6 will always be the last to conduct current when the battery is turned off. Therefore, when the battery is turned on, in accordance with the claimed connections, control pulses are fed primarily to thyristor 5, which is connected counter-parallel to thyristor 6, and then to the other thyristors. This is as follows. Suppose that the command to turn on the battery is received at the maximum speed of the installation during the period immediately following the moment of shutdown (moment ts in Fig. 2). In this case, from the shaper 14 to the installation input of the trigger 15 receives a zero signal, setting a unit at its output. The trigger 16 is no longer held in the zero state and therefore, along the leading edge of the first pulse from the comparator 9 (moment t in Fig. 2), it will switch and a single signal will be established at its output, which, entering the input of the logic element 19, will allow the passage of control pulses to thyristor 5. At this moment, the voltage on thyristor 5 is zero and begins to change in the direction of positive values, so it will turn on without a surge in the charging current. At the same time, a single signal from the output of the trigger 16 goes to the installation inputs of the triggers 17 and 18, preparing them for control- / yy //

synchronization input. Therefore, at the time tv, the leading edge of the corresponding signal coming from the output of the comparator 10, the trigger 17 will switch to a single state, thereby allowing the passage of control pulses to thyristors 3 and 6. Since at the same moment on the thyristor 3 there is a blocking polarity of the anode voltage, then it will not turn on until the voltage at its anode becomes positive, i.e. until the next mains voltage period. For thyristor 6, at this moment, the anode voltage goes through zero to the side of positive values, so it will turn on without a surge in current. Finally, at time tg, trigger 18 will switch and allow the passage of control pulses to thyristor 4. The turn-on process ends, and the battery is symmetrically connected to the network.

If the battery is switched on with fully or partially discharged capacitors, the control circuit works similarly in terms of the moment of supply of control pulses for each of the thyristors. However, the nature of the voltage change across the capacitors and thyristors of the installation in this case becomes somewhat different. Pa fig. 3 shows the process of turning on a fully discharged battery in the inventive switching device. Upon receipt of the command to turn on the battery at time t4, the thyristor 5 will not turn on when the control pulses (ts) are applied to it, but only after the voltage at its anode becomes zero and begins to change in the direction of positive values. The voltage at the thyristor 3 after the supply of control pulses to it will become a trigger

earlier than the control pulses will be applied to the thyristor 4, so first thyristor 3, and then thyristor 4.

Thus, the claimed device enables the battery to be switched on without current spikes at any value of the residual charge of the capacitors with the maximum possible speed for natural switching, as well as limiting the maximum voltage on the thyristors within the double amplitude value of the mains voltage.

Claims (1)

A device for contactless switching a three-phase capacitor bank, comprising a three-phase capacitor bank with an internal phase connection in a triangle connected to a three-phase AC network via semiconductor switches, and a control system including a three-phase synchronization transformer connected to the network, three comparators, pulse transformers, command generator controls, synchronous triggers, a high-frequency pulse generator, logic elements, pulse amplifiers, while the input inputs of the second and third triggers are connected to the non-inverting output of the first trigger, one of the inputs of the logic elements is connected to the output of the corresponding trigger, and the second inputs of all logic elements are connected to the output of the high-frequency pulse generator, the outputs of all logic elements are connected to the inputs of the corresponding pulse amplifiers, the outputs of which , in turn, through pulse transformers connected to the control circuits of the thyristors of semiconductor switches, characterized in that about о contains an additional fourth synchronous trigger, semiconductor switches are made in the form of two pairs of counter-parallel connected thyristors included in two linear wires of phases “A” and “C” of the capacitor bank, one of the pulse transformers is made in three-winding design, the secondary windings are “s The "and" in the synchronizing transformer are connected respectively to the inverting and non-inverting inputs of the first comparator, and the phase winding "a" of the same transformer is connected to the inverting input of the second comparator and the non-inverting input of the third comparator, in which other inputs are connected to the chassis bus, the synchronizing inputs of the second and fourth triggers are connected together and connected to the output of the third comparator, and the same inputs of the first and third triggers are connected respectively to the outputs of the second and first comparators, information inputs all triggers are connected to the positive pole of the power source, the installation input of the fourth trigger is connected to the output of the control command generator, the same input of the first trigger pa is connected to the inverting output of the fourth trigger, and the outputs of the first and third pulse amplifiers are connected through two-winding pulse transformers to the control circuits of the direct thyristor phase “C” and reverse thyristor phase “A” of the semiconductor switch, and the output of the second pulse amplifier is connected through the aforementioned three-winding pulse a transformer, respectively, to the control circuits of two other thyristors of the same first and second pair of thyristors of a semiconductor switch.