Three-phase alternating current three-potential rectifying circuit

Abstract

The invention discloses a three-phase alternating current three-potential rectifying circuit, which is particularly applied to a power supply circuit of a three-phase alternating current combination switch. According to a traditional combination switch, a magnetic latching relay is used for improving withstand voltage between a contact and a coil and preventing inter-phase short circuit caused by sparking between the contact and the coil, and the magnetic latching relay is high in cost and short in service life. Three phase line relays of the three-phase alternating-current composite switch powered by the three-phase alternating-current three-potential rectifying circuit are respectively powered by three non-common-ground power supplies, so that even if a common relay is adopted, the problem of sparking short circuit between a relay contact and a coil cannot occur; therefore, the problem of interphase short circuit of the three-phase alternating-current composite switch is effectively solved, the reliability of the switch is greatly improved, and the cost is reduced.

Description

Technical Field

[0001] The invention relates to a three-phase alternating current three-potential rectification circuit, in particular to a relay power supply circuit of a three-phase alternating current relay switch. Background Art

[0002] Three-phase AC composite switches are widely used in the switching of three-phase AC capacitors for low-voltage reactive power compensation. Existing three-phase AC composite switches use one power supply to power the relays on the three phase lines at the same time. Due to the large voltage difference between the contacts and coils of the switch, once the withstand voltage between the contacts and coils of the two relays drops and sparks occur, it will cause a phase-to-phase short circuit, which is commonly known as the switch explosion. The general solution is to increase the distance between the contacts and coils of the relay, or to completely isolate the contacts and coils, or to increase the insulation of the coils. Magnetic latching relays can meet the above requirements, but the result is an increase in the cost of the relays, and the mechanical life of the relays is much lower than that of ordinary electromagnetic relays due to the complex mechanical structure of the relays. Although the magnetic latching relays improve the withstand voltage between the contacts and coils of the relays, they cannot fundamentally solve the problem of short circuits between the contacts and coils. In addition, the above solutions have no substantial improvement effect on some smaller relays. Summary of the invention

[0003] In order to solve the problem that the existing three-phase AC composite switch is prone to sparking due to insufficient voltage resistance of relay contacts and coils, the present invention provides a three-phase AC three-potential rectifier circuit, which makes the voltage difference between the contacts and coils of the relays working on the three phase lines very small, and even if ordinary relays are used, the sparking phenomenon between the contacts and the coil can be avoided.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is as follows: the three-phase AC three-potential rectifier circuit of the present invention is composed of three rectifier bridges Qa, Qb, Qc of the three phases A, B, and C and two step-down capacitors Ca and Cc, one AC input end of the A-phase rectifier bridge Qa is connected to the A phase, and the other AC input end is connected to an AC input end of the B-phase rectifier bridge Qb through the step-down capacitor Ca, one AC input end of the C-phase rectifier bridge Qc is connected to the C phase, and the other AC input end is connected to an AC input end of the B-phase rectifier bridge Qb through the step-down capacitor Cc, one AC input end of the B-phase rectifier bridge Qb is connected to the B phase, and the other AC input end is connected to the common end of the step-down capacitors Ca and Cc, each rectifier bridge Qa, Qb and Qc DC output is connected to the coil of the corresponding relay Ja, Jb and Jc, and the DC output of the B-phase rectifier bridge also provides power for the control circuit.

[0005] Furthermore, an AC input terminal of the B-phase rectifier bridge Qb is connected to the B-phase through a series circuit of a fuse FU and a current limiting circuit Rb.

[0006] The present invention has the following advantages:

[0007] The three-phase AC three-potential rectifier circuit of the present invention provides a power supply circuit for the three-phase relays of the three-phase AC composite switch, which can ensure that there is no spark breakdown between the contacts and the coil of the relay, thereby ensuring that there is no interphase short circuit inside the three-phase AC composite switch. The three-phase AC composite switch can use ordinary low-cost relays to achieve higher reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is one of the schematic diagrams of the three-phase alternating current three-potential rectification circuit of the present invention;

[0009] Figure 2 This is the second schematic diagram of the three-phase AC three-potential rectification circuit of the present invention;

[0010] Figure 3 This is the third schematic diagram of the three-phase AC three-potential rectifier circuit of the present invention;

[0011] Figure 4 This is the fourth schematic diagram of the three-phase AC three-potential rectification circuit of the present invention.

[0012] Specific embodiment description

[0013] like Figure 1 The three-phase AC three-potential rectifier circuit of the present invention is shown as follows: it is composed of three rectifier bridges Qa, Qb, Qc of three phases A, B, and C and two step-down capacitors Ca and Cc, one AC input end of the A-phase rectifier bridge Qa is connected to the A phase, and the other AC input end is connected to an AC input end of the B-phase rectifier bridge Qb (the input end not connected to the B phase) through the step-down capacitor Ca, one AC input end of the C-phase rectifier bridge Qc is connected to the C phase, and the other AC input end is connected to an AC input end of the B-phase rectifier bridge Qb (the input end not connected to the B phase) through the step-down capacitor Cc, one AC input end of the B-phase rectifier bridge Qb is connected to the B phase, and the other AC input end is connected to the common end of the step-down capacitors Ca and Cc, each rectifier bridge Qa, Qb and Qc DC output is connected to the coil of the corresponding relay Ja, Jb and Jc, and the DC output of the B-phase rectifier bridge also provides power for the control circuit.

[0014] The working principle of the three rectifier bridges is as follows: Figure 1A, B, and C are the three AC input terminals of the three-phase AC switch, and L1, L2, and L3 are the three output terminals of the three-phase AC switch. The A-phase rectifier bridge Qa is provided with an AC input voltage by the AB phase through the step-down capacitor Ca, the C-phase rectifier bridge Qc is provided with an AC input voltage by the BC phase through the step-down capacitor Cc, and the B-phase rectifier bridge Qb is provided with an AC input voltage by the AB and BC phases through the step-down capacitors Ca and Cc. When Ca and Cc are the same size, the output current of the B-phase rectifier bridge is about 1.7 times the output current of the A-phase and C-phase rectifier bridges, and the extra part is just enough to provide current for the control circuit. The outputs of the three rectifier bridges Qa, Qb, and Qc are not grounded together. The grounds of the three rectifier power supplies are the potentials of the corresponding phase voltages. The DC ground potential of the rectifier bridge Qa is basically the A phase potential, the DC ground potential of the rectifier bridge Qb is basically the B phase potential, and the DC ground potential of the rectifier bridge Qc is basically the C phase potential. The three-phase three-phase relays Ja, Jb, and Jc are powered by three power supplies with different ground potentials, respectively. In this way, the maximum voltage between the contacts and coils of the three relays Ja, Jb, and Jc is only the DC voltage output by the rectifier bridges Qa, Qb, and Qc. This voltage cannot cause sparks between the contacts and coils of the relays. The three-phase AC three-potential rectifier circuit of the present invention has basically no requirements for the withstand voltage between the contacts and coils of the relays. Even a relay of very small volume can meet the withstand voltage requirements between the contacts and coils.

[0015] The control circuit controls the transistors in series with the coils of relays Ja and Jc through an optical coupler to meet the withstand voltage requirements between the control circuit and Ja and Jc. The transistors in series with the coil of Jb do not have a voltage difference and can be directly controlled. Figure 1 The principle is not shown in the figure, and it is easy to implement for general technicians, so it will not be described in detail here.

[0016] Figure 2 This is the second embodiment of the three-phase AC three-potential bridge rectifier circuit of the present invention. An input end of the B-phase rectifier bridge Qb connected to the B-phase is connected to the B-phase through a series circuit of a fuse FU and a current limiting circuit Rb, rather than being directly connected to the B-phase. Moreover, the connection point between the fuse and the B-phase is outside the circuit board ( Figure 2 The dotted box is the switch circuit board). The circuit board is designed with the B phase circuit in the middle of the circuit board. The connecting wires at both ends of the B phase relay contact use sheathed wires to prevent short circuits with phases A and C. The A phase circuit and the C phase circuit are on both sides of the B phase circuit. If interphase creepage occurs due to circuit board contamination or other reasons, only a short circuit between phases A and B or between phases C and B can occur, but not between phases A and C. When a short circuit occurs, the current limiting resistor Rb plays a role in limiting the short-circuit current, and if the short circuit time is long, the fuse FU will burn out to prevent the circuit board from burning due to the heat of the short-circuit current, thereby preventing the switch circuit board from short-circuiting and exploding in extreme cases, and avoiding the expansion of short-circuit accidents.

[0017] Figure 3 This is the third embodiment of the three-phase AC three-potential bridge rectifier circuit of the present invention. The A-phase rectifier bridge Qa draws power from the AB phase through the step-down capacitor Ca, the B-phase rectifier bridge Qb draws power from the BC phase through the step-down capacitor Cb, and the C-phase rectifier bridge Qc draws power from the AC phase through the step-down capacitor Cc. The characteristic of this circuit is that the output current of the rectifier bridge of each phase is determined according to the size of the step-down capacitor of each phase. The C-phase rectifier bridge can be allowed to power the control circuit. At this time, the C-phase step-down capacitor Cc should be larger than Ca and Cb, because the output of the C-phase rectifier bridge not only provides power for the relay, but also provides power for the control circuit. Similarly, fuses and current-limiting resistors can be used to solve the problem of circuit board short circuits. The principle is generally understood by technicians according to Figure 2 The embodiments are easy to implement and will not be described in detail here.

[0018] Figure 4 This is the fourth embodiment of the three-phase AC three-potential bridge rectifier circuit of the present invention. This is an embodiment of a transformer isolation power supply. Transformer B takes power from the BC phase and steps down the voltage, and then supplies power to the C phase relay and control circuit through the rectifier bridge Qc. At the same time, the A phase and B phase relays are supplied with power respectively through the DC / DC power supply A and the DC / DC power supply B. Ra connects the ground of the A phase and Qa to ensure that the ground of Qa is the A phase potential; Rb connects the ground of the B phase and Qb to ensure that the ground of Qb is the B phase potential; Rc connects the ground of the C phase and Qc to ensure that the ground of Qc is the C phase potential. In this way, it can be ensured that there is only a small voltage difference between the contacts and coils of the relays Ja, Jb and Jc on the three phase lines A, B and C, which is not enough to generate a sparking voltage between the contacts and the coil, that is, there will be no sparking short circuit between the contacts and the coil.

[0019] Obviously, in the three embodiments Figure 2 The circuit is the simplest and most reliable. Figure 2 A RC step-down power supply is used. The disadvantage of the RC step-down power supply is that the power supply is not isolated. However, in the embodiment of the present invention, the power supply does not need to be isolated, which just brings into play the advantages of the RC step-down power supply.

[0020] The withstand voltage between the contacts and the coil of the relay is an important indicator of the power relay. If the withstand voltage is too low, the contacts and the coil will spark. In order to prevent the problem of sparking between the contacts and the coil of the relay, the general solution is to find a way to increase the distance between the contacts and the coil and improve the insulation of the coil surface. The result of doing so will increase the volume of the relay on the one hand, and increase the cost of the relay on the other hand. The solution provided by the present invention is to reduce the voltage between the contacts and the coil through the design of the power supply, and reduce the voltage to tens of volts or even more than ten volts where air ionization is impossible to produce, that is, fundamentally solve the possibility of short circuit between the three-phase line relays. It seems that anyone can think of a very simple circuit, but there is a profound first principle hidden here. Power relays are widely used in the control of single-phase loads, but the control of three-phase loads has never been controlled by three single-phase relays. The circuit of the three-phase alternating current three-potential rectification of the present invention will provide a new idea for the design of three-phase power switches.

[0021] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase AC three-potential rectifier circuit: composed of three rectifier bridges Qa, Qb, Qc of three phases A, B, and C and two step-down capacitors Ca and Cc, one AC input end of the A-phase rectifier bridge Qa is connected to the A phase, and the other AC input end is connected to an AC input end of the B-phase rectifier bridge Qb through the step-down capacitor Ca, one AC input end of the C-phase rectifier bridge Qc is connected to the C phase, and the other AC input end is connected to an AC input end of the B-phase rectifier bridge Qb through the step-down capacitor Cc, one AC input end of the B-phase rectifier bridge Qb is connected to the B phase, and the other AC input end is connected to the common end of the step-down capacitors Ca and Cc, each rectifier bridge Qa, Qb and Qc DC output is connected to the coil of the corresponding relay Ja, Jb and Jc, and the DC output of the B-phase rectifier bridge also provides power for the control circuit.

2. The three-phase alternating current three-potential rectifier circuit according to claim 1, It is characterized in that An AC input end of the B-phase rectifier bridge Qb is connected to the B-phase through a series circuit of a fuse FU and a current limiting circuit Rb.

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