Broken line protection circuit for secondary circuit of current transformer

Abstract

The utility model relates to the technical field of current transformer secondary circuit safe power supply, and particularly discloses a current transformer secondary circuit disconnection protection circuit, which comprises a bidirectional silicon controlled rectifier circuit, a detection circuit and a photoelectric isolation driving circuit, and is characterized in that an anode and a cathode of a bidirectional silicon controlled rectifier VT are connected in parallel on a secondary coil of a current transformer; the control electrode G of the bidirectional silicon controlled rectifier VT is connected with the output end of the photoelectric isolation driving circuit; the secondary coil of the current transformer is also connected in parallel with a detection circuit; the output end of the detection circuit is connected with a photoelectric isolation driving circuit; the voltage dependent resistor of the detection circuit is in a high-resistance state when the current transformer works normally, the trigger circuit of the bidirectional thyristor VT is switched on through the photoelectric isolation driving circuit, so that the bidirectional thyristor VT is switched on rapidly, the secondary side of the current transformer is short-circuited and closed, accidents are avoided, other components in a secondary circuit are effectively protected from overvoltage damage, and the service life of the current transformer is prolonged. And safe and reliable operation of the secondary circuit equipment of the current transformer is ensured.

Description

Technical Field

[0001] The utility model relates to the technical field of safe power supply of a secondary circuit of a current transformer, in particular to a wire break protection circuit of a secondary circuit of a current transformer. Background Art

[0002] The current transformer is an electrical device that converts the large current on the primary side into a small secondary current that can be used for metering, measurement and protection. The secondary load impedance of the current transformer is very small, and it is basically in a short-circuit state. Under normal circumstances, the magnetic potential of the primary and secondary coils of the current transformer is balanced. When the secondary circuit of the current transformer is open, the current flowing through the primary coil is completely converted into the excitation current of the current transformer, causing the core magnetic flux of the current transformer to rise sharply and the core to saturate. At this time, a high voltage will be induced at both ends of the secondary coil, with a peak value of several thousand volts or even tens of thousands of volts, causing increased core loss and severe heat generation, causing the insulation of instruments, protection devices and other equipment connected in series on the secondary circuit of the current transformer to be damaged and eventually burn out, endangering the personal safety of the operating personnel. At the same time, it causes inaccurate metering and measurement of electric energy, resulting in false operation and refusal of relay protection.

[0003] In the prior art, when the secondary circuit of the operating current transformer is broken or open, the current terminals and component wire ends of the secondary circuit of the current transformer will discharge and spark, and the current transformer body will also make abnormal sounds. Generally, the secondary circuit of the current transformer is short-circuited at the secondary current terminal block by using a special short-circuit wire, but it poses a certain threat to the personal safety of the staff and has a high safety risk; or the power is cut off for processing, but it will affect the reliable and continuous power supply to users. For this reason, a current transformer secondary circuit break protection circuit is developed to solve the problems of high short-circuit safety risk when the secondary circuit of the existing current transformer is broken or open, and the power outage processing affects the continuous power supply. Utility Model Content

[0004] In view of the problems existing in the prior art, the utility model aims to provide a current transformer secondary circuit break protection circuit.

[0005] The utility model solves the technical problem by adopting the following technical scheme: a current transformer secondary circuit disconnection protection circuit, comprising a bidirectional thyristor circuit, a detection circuit and a photoelectric isolation drive circuit, wherein the bidirectional thyristor circuit comprises a bidirectional thyristor VT, an anode and a cathode of the bidirectional thyristor VT are connected in parallel to the secondary coil of the current transformer, and a control electrode G of the bidirectional thyristor VT is connected to the output end of the photoelectric isolation drive circuit; the secondary coil of the current transformer is also connected in parallel with a detection circuit, and the output end of the detection circuit is connected to the photoelectric isolation drive circuit.

[0006] Specifically, the detection circuit includes a varistor RV, a voltage collection resistor R3, a protection resistor R4 and a bridge rectifier circuit. The varistor RV, the voltage collection resistor R3 and the protection resistor R4 connected in series are connected in parallel to the secondary coil of the current transformer. The input end of the bridge rectifier circuit is connected in parallel to the two ends of the voltage collection resistor R3, and the output end of the bridge rectifier circuit is connected to the photoelectric isolation drive circuit.

[0007] Specifically, the photoelectric isolation drive circuit includes a photoelectric coupler U2, a relay K, and a transistor V2. The collector c end of the photoelectric coupler U2 is connected to one end of the relay K coil, the negative electrode of the freewheeling diode VD5 and the positive electrode VCC of the DC power supply, and the emitter e end of the photoelectric coupler U2 is connected to the base of the transistor V2; the collector of the transistor V2 is connected to the other end of the relay K coil and the positive electrode of the freewheeling diode VD5, and the emitter of the transistor V2 is connected to the protection resistor R7 and then connected to the negative electrode GND of the DC power supply; one end of the normally open contact of the relay K is connected to the control electrode G of the bidirectional thyristor VT, and the other end of the relay K is connected to the secondary coil of the current transformer.

[0008] Specifically, the model of the photoelectric coupler U2 is 4N25.

[0009] Specifically, the voltage of the DC power supply is 5V.

[0010] Specifically, the model of the bidirectional thyristor VT is BT136.

[0011] Specifically, the secondary coil measuring current terminals S1 and S2 of the current transformer are connected by 2.5mm 2 The single-strand copper core wires are respectively connected to component boards made of protection circuits, and the component boards made of protection circuits are installed on metal guide rails where current terminal blocks of a switch cabinet control cabinet door are located.

[0012] The utility model has the following beneficial effects:

[0013] The utility model discloses a current transformer secondary circuit disconnection protection circuit, which can quickly operate when an open circuit suddenly appears on the secondary side of the current transformer during operation, so as to close the secondary loop of the current transformer and ensure the safe and reliable operation of the current transformer secondary circuit equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural diagram of the installation and wiring of the current transformer secondary circuit break protection circuit.

[0015] Figure 2 It is the circuit diagram of the current transformer secondary circuit break protection circuit. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely further describe the technical solutions in the embodiments of the utility model. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0017] Embodiment 1.

[0018] like Figure 1 As shown in the figure, CTB is a component board for the current transformer secondary circuit break protection circuit. It can be directly installed on the metal rail where the current terminal block of the switch cabinet control cabinet door is located, and then connected to the 2.5mm 2 The single-strand copper core conductor is connected in parallel with the secondary coil current terminals S1 and S2 of the current transformer.

[0019] like Figure 2 As shown, a current transformer secondary circuit disconnection protection circuit includes a bidirectional thyristor circuit, a detection circuit and a photoelectric isolation drive circuit. The bidirectional thyristor circuit includes a bidirectional thyristor VT. The anode and cathode of the bidirectional thyristor VT are connected in parallel to the secondary coil of the current transformer, and the control electrode G of the bidirectional thyristor VT is connected to the output end of the photoelectric isolation drive circuit; the secondary coil of the current transformer is also connected in parallel with the detection circuit, and the output end of the detection circuit is connected to the photoelectric isolation drive circuit.

[0020] The detection circuit includes a varistor RV, a voltage collection resistor R3, a protection resistor R4 and a bridge rectifier circuit. The varistor RV, the voltage collection resistor R3 and the protection resistor R4 connected in series are connected in parallel to the secondary coil of the current transformer. The input end of the bridge rectifier circuit is connected in parallel to the two ends of the voltage collection resistor R3, and the output end of the bridge rectifier circuit is connected to the photoelectric isolation drive circuit.

[0021] The photoelectric isolation driving circuit includes a photoelectric coupler U2, a relay K, and a transistor V2. The collector c end of the photoelectric coupler U2 is connected to one end of the relay K coil, the negative electrode of the freewheeling diode VD5, and the positive electrode VCC of the DC power supply. The emitter e end of the photoelectric coupler U2 is connected to the base of the transistor V2; the collector of the transistor V2 is connected to the other end of the relay K coil and the positive electrode of the freewheeling diode VD5, the emitter of the transistor V2 is connected to the protection resistor R7 and then connected to the negative electrode GND of the DC power supply; one end of the normally open contact of the relay K is connected to the control electrode G of the bidirectional thyristor VT, and the other end of the relay K is connected to the secondary coil of the current transformer.

[0022] The model of the photocoupler U2 is 4N25. The chip is a dual in-line device with 6 external leads. The input light emitter is composed of a light-emitting diode, pin 1 is the anode, pin 2 is the cathode, and the output light receiver is composed of a phototransistor, pin 4 is the emitter, pin 5 is the collector, pin 6 is the base, and pin 3 is an empty pin.

[0023] The voltage of the DC power supply is 5 V. The model of the bidirectional thyristor VT is BT136.

[0024] The installation size of the component board made of the current transformer secondary circuit disconnection protection circuit is 50mm×50mm, which is similar to the conventional current terminal. The overall size is 56mm long×16mm wide×25mm high. It can be directly installed on the metal rail where the current terminal block of the switch cabinet control cabinet door is located. 2 The single-strand copper core conductor is respectively connected in parallel with the secondary measuring current terminals 1S1, 1S2, the secondary protection current terminals 2S1, 2S2, and the secondary metering current terminals 3S1, 3S2 of the current transformer.

[0025] Embodiment 2, the working principle of the current transformer secondary circuit break protection circuit adopting the circuit structure of embodiment 1.

[0026] When the secondary circuit of the current transformer is open, a sudden voltage will appear. After passing through the varistor RV, the voltage collection resistor R3, and the protection resistor R4, the resistance of the varistor RV changes, and the collected voltage UR3 passes through the diode bridge rectifier VD1-VD4 to the primary side pins 1 and 2 of the optocoupler U2.

[0027] (1) Detection circuit: Under normal voltage conditions, the varistor RV is equivalent to a small capacitor. When the secondary circuit of the current transformer is open and overvoltage occurs, the internal resistance drops sharply and quickly turns on. The operating current can increase by several orders of magnitude, which can effectively protect other components in the secondary circuit from overvoltage damage.

[0028] (2) Photoelectric isolation drive circuit: After the primary side of the photocoupler U2 is activated, the secondary side is turned on. The e-terminal of the photocoupler U2 is at a high level, the transistor V2 is turned on, the relay K is activated, and its normally open contact is energized, connecting the trigger circuit of the bidirectional thyristor (bidirectional thyristor VT), so that the bidirectional thyristor VT is quickly turned on, short-circuiting the secondary side of the current transformer to close the loop and avoid accidents. The maximum operating current of the bidirectional thyristor VT is equal to the secondary operating current of the current transformer.

[0029] Photocoupler U2, also known as photoelectric isolator, is an electric-optical-electrical conversion device, which consists of two parts: a light source and a light receiver. It uses light as a medium to transmit electrical signals. When an electrical signal is applied to the input end of the photocoupler U2, the light source emits light, and the intensity of the light depends on the magnitude of the excitation current. After this light is irradiated on the light receiver packaged together, a photocurrent is generated due to the photoelectric effect, which is led out from the output end of the light receiver, realizing the electric-optical-electrical conversion. Through the control of the photocoupler U2, the input and output electrical signals can be well isolated.

[0030] The current transformer secondary circuit break protection circuit can act quickly when an open circuit suddenly appears on the secondary side during the operation of the current transformer, so as to close the secondary loop of the current transformer and ensure the safe and reliable operation of the secondary circuit of the current transformer.

[0031] The present utility model is not limited to the above-mentioned implementation modes, and anyone should be aware of the structural changes made under the inspiration of the present utility model. Any technical solutions that are the same or similar to the present utility model fall within the protection scope of the present utility model.

[0032] The technology, shape and structure parts not described in detail in the present invention are all known technologies.

Claims

1. A current transformer secondary circuit disconnection protection circuit, characterized in that: It includes a bidirectional thyristor circuit, a detection circuit and a photoelectric isolation drive circuit. The bidirectional thyristor circuit includes a bidirectional thyristor VT. The anode and cathode of the bidirectional thyristor VT are connected in parallel to the secondary coil of the current transformer. The control electrode G of the bidirectional thyristor VT is connected to the output end of the photoelectric isolation drive circuit. The secondary coil of the current transformer is also connected in parallel with the detection circuit, and the output end of the detection circuit is connected to the photoelectric isolation drive circuit. The detection circuit includes a varistor RV, a voltage collection resistor R3, a protection resistor R4 and a bridge rectifier circuit. The varistor RV, the voltage collection resistor R3 and the protection resistor R4 connected in series are connected in parallel to the secondary coil of the current transformer. The input end of the bridge rectifier circuit is connected in parallel to both ends of the voltage collection resistor R3. The output end of the bridge rectifier circuit is connected to the photoelectric isolation drive circuit. The photoelectric isolation driving circuit includes a photoelectric coupler U2, a relay K, and a transistor V2. The collector c end of the photoelectric coupler U2 is connected to one end of the relay K coil, the negative electrode of the freewheeling diode VD5, and the positive electrode VCC of the DC power supply. The emitter e end of the photoelectric coupler U2 is connected to the base of the transistor V2; the collector of the transistor V2 is connected to the other end of the relay K coil and the positive electrode of the freewheeling diode VD5, the emitter of the transistor V2 is connected to the protection resistor R7 and then connected to the negative electrode GND of the DC power supply; one end of the normally open contact of the relay K is connected to the control electrode G of the bidirectional thyristor VT, and the other end of the relay K is connected to the secondary coil of the current transformer.

2. The current transformer secondary circuit disconnection protection circuit according to claim 1, characterized in that: The model of the photocoupler U2 is 4N25.

3. The current transformer secondary circuit disconnection protection circuit according to claim 1, characterized in that: The voltage of the DC power supply is 5V.

4. The current transformer secondary circuit disconnection protection circuit according to claim 1, characterized in that: The model of the bidirectional thyristor VT is BT136.

5. The current transformer secondary circuit disconnection protection circuit according to claim 1, characterized in that: The secondary coil of the current transformer measures the current through terminals S1 and S2 through 2.5mm 2 The single-strand copper core wires are respectively connected to component boards made of protection circuits, and the component boards made of protection circuits are installed on metal guide rails where current terminal blocks of a switch cabinet control cabinet door are located.

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