CN210297238U

CN210297238U - Overcurrent protection circuit of three-phase motor

Info

Publication number: CN210297238U
Application number: CN201920887382.2U
Authority: CN
Inventors: 张友表
Original assignee: Yuyao Rongxing Electric Co Ltd
Current assignee: Yuyao Rongxing Electric Co Ltd
Priority date: 2019-06-13
Filing date: 2019-06-13
Publication date: 2020-04-10
Anticipated expiration: 2029-06-13

Abstract

The utility model discloses an overcurrent protection circuit of a three-phase motor, which comprises a main circuit and an overcurrent protection circuit; the main circuit comprises a low-voltage circuit breaker, a first normally open contact, a first phase line, a second phase line, a third phase line and a three-phase motor, wherein the first phase line, the second phase line and the third phase line are respectively connected to the three-phase motor through the voltage circuit breaker and the first normally open contact; the overcurrent protection circuit comprises a change-over switch, a control switch, a relay, a second normally open contact, a first current transformer, a second current transformer, a potentiometer, a first triode, a second triode, a third triode and a fourth triode, wherein the first end of the change-over switch is connected to the second phase line. The utility model relates to a three-phase motor's overcurrent protection circuit, the reinforcing is to the overcurrent protection in the alternating current motor circular telegram work to improve alternating current motor's life.

Description

Overcurrent protection circuit of three-phase motor

Technical Field

The utility model relates to an overcurrent protection technical field especially relates to a three-phase motor's overcurrent protection circuit.

Background

Overcurrent protection is a protection mode in which a protection device is activated when a current exceeds a predetermined maximum value. When the current flowing through the protected original exceeds a preset value, the protection device is started, and the selectivity of action is ensured by time limit, so that the circuit breaker trips or gives an alarm signal. Overcurrent protection mainly includes two types of short-circuit protection and overload protection. The short-circuit protection is characterized by large setting current and instantaneous action.

An ac motor is a machine for converting mechanical energy and ac power into each other. Because of the huge development of the alternating current power system, the alternating current motor becomes the most commonly used motor, and the alternating current motor has the advantages of simple structure, convenient manufacture and easy manufacture into a motor with high rotating speed, high voltage, large current and large capacity due to no commutator, and is widely applied to power parts of various mechanical equipment, the coverage range of the alternating current motor power is very large, from a few watts to hundreds of thousands of kilowatts, even millions of kilowatts, but the fuse is easily burnt down by the over current during the startup of the alternating current motor when the alternating current motor is used, the fuse needs to be frequently replaced, so that inconvenience is brought to users, and the service life of the alternating current motor can be influenced.

SUMMERY OF THE UTILITY MODEL

Technical problem to be solved

The utility model aims to solve the problem that an overcurrent protection circuit of three-phase motor is provided, the reinforcing is to the overcurrent protection in the alternating current motor circular telegram work to improve alternating current motor's life.

(II) technical scheme

In order to achieve the above object, the present invention provides an overcurrent protection circuit for a three-phase motor, which comprises a main circuit and an overcurrent protection circuit; the main circuit comprises a low-voltage circuit breaker, a first normally open contact, a first phase line, a second phase line, a third phase line and a three-phase motor, wherein the first phase line, the second phase line and the third phase line are respectively connected to the three-phase motor through the voltage circuit breaker and the first normally open contact;

the overcurrent protection circuit comprises a change-over switch, a control switch, a relay, a second normally open contact, a first current transformer, a second current transformer, a potentiometer, a first triode, a second triode, a third triode and a fourth triode, wherein the first end of the change-over switch is connected to the second phase line, a normally open contact of the relay is connected with the second normally open contact in series and then connected with the control switch in parallel, and the second end of the change-over switch is connected with the primary side of the second current transformer through a parallel circuit;

a primary side of the first current transformer is connected in series with the third phase line, a secondary side of the first current transformer is connected with a base of the first triode and a base of the third triode through the potentiometer, a first diode for rectification is connected between the secondary side of the first current transformer and a first end of the potentiometer, a second end of the potentiometer is connected with the base of the first triode, a third end of the potentiometer is connected in series with a first resistor for voltage division, an emitter of the first triode is connected with a collector of the third triode, an emitter of the third triode is grounded, and a first end of the secondary side of the second current transformer is connected with a collector of the second triode and a collector of the fourth triode respectively through a fourth diode and a coil of the relay, and the emitting electrode of the fourth triode is grounded, and the base electrode of the fourth triode is connected with the negative electrode of the second diode.

The first current transformer outputs current through a secondary side, the current is rectified through a first diode, voltage signals are formed through voltage division of a potentiometer and a first resistor, the formed voltage signals are added to a base electrode of a first triode through a second resistor and a sixth diode, and the other signals are added to a base electrode of a third triode through the potentiometer; the first triode, the second triode and the third triode form an emitter coupled bistable circuit, and in a normal state, the first triode is in a cut-off state, the second triode and the third triode are in a saturated conduction state, a coil of the relay is electrified, a normally open switch of the relay is closed, and the alternating current motor operates normally; when one of the three phases is in phase failure, the current is increased more than normal or the current is increased due to faults such as short circuit of an alternating current motor coil, mechanical blockage and the like, at the moment, the current of the secondary side of the first current transformer is increased, the base voltage added to the first triode is also increased, the first triode and the third triode are enabled to be in a saturated conduction state, the second triode is cut off, the coil of the relay loses power, the normally open switch of the relay is released at the same time, the coil loses power in succession, the second normally open contact is released, the first normally open contact is disconnected, the three phases are not powered any more, and the alternating current motor is protected in an overcurrent state.

Further, the over-current protection circuit further comprises a first capacitor, a second capacitor, a third diode, a fifth diode, a sixth diode, a second resistor, a third resistor, a fourth resistor and a fifth resistor, wherein the anode of the first capacitor is connected with the cathode of the first diode, the cathode of the first capacitor is grounded, the second resistor and the sixth diode are connected in series between the second end of the potentiometer and the base of the first triode, the third diode is connected between the emitter of the first triode and the collector of the third triode, the third resistor and the fourth resistor are connected in parallel between the cathode of the fourth diode and the base of the second triode, the second capacitor and the fifth resistor are connected in series between the cathode of the second diode and the base of the fourth triode, and the cathode of the fifth diode is connected with the base of the fourth triode, and the anode of the fifth diode is grounded.

Further, the first triode, the second triode and the third triode form an emitter-coupled bistable circuit.

Further, still include fuse and coil, second current transformer passes through the fuse with first phase line is connected and is formed the return circuit, the coil connect in parallel circuit with between the second current transformer.

Further, the first triode, the second triode, the third triode and the fourth triode are respectively NPN type triodes.

Further, the first capacitor is connected in parallel between the first end of the potentiometer and the first resistor and used for storing the current of the secondary side of the first current transformer, and the second capacitor is connected in parallel between the cathode of the second diode and the base of the fourth triode and used for storing the current of the secondary side of the second current transformer.

Further, the emitter-coupled bistable circuit comprises two states, the first current transformer outputs current through a secondary side, the potentiometer and the first resistor divide the voltage to form a voltage signal, the voltage signal is input to the base electrode of the first triode, when the voltage signal is smaller than a rated voltage value, the overcurrent protection circuit is in a state that the first triode is cut off, and the second triode and the third triode are in a saturated conduction state; when the voltage signal is greater than the rated voltage value, the overcurrent protection circuit is in a saturation conduction state of the first triode and the third triode, and the second triode is in a cut-off state.

(III) advantageous effects

Compared with the prior art, the technical scheme of the utility model have following advantage: the utility model discloses utilize four triodes and relay and a plurality of conduction component to constitute overcurrent protection circuit, first triode, an emitter coupling bistable circuit is constituteed to second triode and third triode, under the normal condition, first triode is in the off-state, second triode and third triode are in the saturation conducting state, the coil of relay gets electricity, the normally open switch actuation of relay, alternating current motor normally works, otherwise, when a certain looks open phase in the three phases, first current transformer's secondary side current increase, at this moment, first triode and third triode are in the saturation conducting state, the second triode ends, relay coil lost point release relay normally open switch, alternating current motor stop work, effectual alternating current motor to when overflowing protects, alternating current motor's life has been improved.

Drawings

Fig. 1 is a circuit diagram of an overcurrent protection circuit of a three-phase motor according to the present invention;

the corresponding part names for the various reference numbers in the figures are: QF is a low-voltage circuit breaker, a is a first phase line, B is a second phase line, C is a third phase line, M is a three-phase motor, STP is a transfer switch, ST is a control switch, K is a relay, KM1 is a first normally open contact, KM2 is a coil, KM3 is a second normally open contact, T1 is a first current transformer, T2 is a second current transformer, RP is a potentiometer, VT1 is a first triode, VT2 is a second triode, VT3 is a third triode, VT4 is a fourth triode, C1 is a first capacitor, C2 is a second capacitor, VD1 is a first diode, VD2 is a second diode, VD3 is a third diode, VD 84 is a fourth diode, VD5 is a fifth diode, VD6 is a sixth diode, R1 is a first resistor, R2 is a second resistor, R585 is a third resistor, R4 is a fourth resistor, VD 3724 is a fifth resistor, and FU is a fuse 573 resistor.

Detailed Description

In this embodiment:

the following detailed description of the embodiments of the present invention is provided with reference to the accompanying drawings and examples. The following examples are intended to illustrate the invention, but are not intended to limit the scope of the invention.

As shown in fig. 1, an overcurrent protection circuit of a three-phase motor includes a main circuit and an overcurrent protection circuit; the main circuit comprises a low-voltage circuit breaker QF, a first normally-open contact KM1, a first phase line A, a second phase line B, a third phase line C and a three-phase motor M, wherein the first phase line A, the second phase line B and the third phase line C are respectively connected to the three-phase motor M through the voltage circuit breaker QF and a first normally-open contact KM 1; the overcurrent protection circuit comprises a transfer switch STP, a control switch ST, a relay K, a second normally-open contact KM3, a first current transformer T1, a second current transformer T2, a potentiometer RP, a first triode VT1, a second triode VT2, a third triode VT3 and a fourth triode VT4, wherein the first end of the transfer switch STP is connected to a second phase line B, the normally-open contact of the relay K is connected with the second normally-open contact KM3 in series and then connected with the control switch ST in parallel, and the second end of the transfer switch STP is connected with the primary side of the second current transformer T2 through a parallel circuit; the primary side of the first current transformer T1 is connected in series on the third phase line C, the secondary side of the first current transformer T1 is connected on the base of the first triode VT1 and the base of the third triode VT3 through the potentiometer RP, a first diode VD1 for rectification is connected between the secondary side of the first current transformer T1 and the first end of the potentiometer RP, the second end of the potentiometer RP is connected with the base of the first triode VT1, the third end of the potentiometer RP is connected in series with a first resistor R1 for voltage division, the emitter of the first triode VT1 is connected with the collector of the third triode VT3, the emitter of the third triode VT3 is grounded, the first end of the secondary side of the second current transformer T2 is connected with the collector of the second triode VT2 and the collector of the fourth triode VT4 through the coils of the fourth diode VD4 and the relay K, the emitter of the fourth triode 4 is grounded, the base of the fourth triode VT4 is connected with the cathode of the second diode VD 2.

The overcurrent protection circuit further comprises a first capacitor C1, a second capacitor C2, a third diode VD3, a fifth diode VD5, a sixth diode VD6, a second resistor R2, a third resistor R3, a fourth resistor R4 and a fifth resistor R5, wherein the anode of the first capacitor C1 is connected with the cathode of the first diode VD1, the cathode of the first capacitor C1 is grounded, the second resistor R2 and the sixth diode VD6 are connected in series between the second end of the potentiometer RP and the base of the first transistor VT1, the third diode VD1 is connected between the emitter of the first transistor VT1 and the collector of the third transistor VT1, the third resistor R1 and the fourth resistor R1 are connected in parallel between the cathode of the fourth diode VD1 and the base of the second transistor VT1, the second capacitor C1 and the fifth resistor R1 are connected in series between the cathode of the second diode VD1 and the base of the fourth diode VD1, the base of the fourth transistor VD1 and the base of the transistor VD1, the anode of the fifth diode VD5 is grounded. The first transistor VT1, the second transistor VT2 and the third transistor VT3 form an emitter-coupled bistable circuit. The overcurrent protection circuit further comprises a fuse FU and a coil KM2, wherein a second current transformer T2 is connected with the first phase line A through the fuse FU to form a loop, and the coil KM2 is connected between the parallel circuit and the second current transformer T2. The first triode VT1, the second triode VT2, the third triode VT3 and the fourth triode VT4 are NPN type triodes respectively.

The first capacitor C1 is connected in parallel between the first terminal of the potentiometer RP and the first resistor R1 for storing the current at the secondary side of the first current transformer T1, and the second capacitor C2 is connected in parallel between the negative electrode of the second diode VD2 and the base of the fourth transistor VT4 for storing the current at the secondary side of the second current transformer T2. The emitter-coupled bistable circuit comprises two states, wherein a first current transformer T1 outputs current through the secondary side, a potentiometer RP and a first resistor R1 divide the voltage to form a voltage signal, the voltage signal is input to the base electrode of a first triode VT1, when the voltage signal is smaller than a rated voltage value, the overcurrent protection circuit is in a state that the first triode VT1 is cut off, and a second triode VT2 and a third triode VT3 are in a saturated conduction state; when the voltage signal is greater than the rated voltage value, the overcurrent protection circuit is in a state that the first triode VT1 and the third triode VT3 are in saturated conduction, and the second triode VT2 is in a cut-off state.

Referring to fig. 1, when the control switch ST is pressed, the second normally open contact KM3 is closed, the first normally open contact KM1 is closed, the alternating current motor M starts to operate, and the operation of the alternating current motor M can be controlled by the transfer switch STP; the first current transformer T1 outputs current through the secondary side, the current is rectified through a first diode VD1, voltage signals are formed through the voltage division of a potentiometer RP and a first resistor R1, the formed voltage signals are added to the base electrode of a first triode VT1 through a second resistor R2 and a sixth diode VD6, and the other signals are added to the base electrode of a third triode VT3 through the potentiometer RP; the first triode VT1, the second triode VT2 and the third triode VT3 form an emitter coupled bistable circuit, in a normal state, the first triode VT1 is in a cut-off state, the second triode VT2 and the third triode VT3 are in a saturated conduction state, a coil of the relay K is electrified, a normally open switch of the relay K is attracted, and the alternating current motor M operates normally; when one of the three phases is out of phase, the current is increased more than normal or the current is increased due to faults such as short circuit of a coil of the alternating current motor M, mechanical blockage and the like, at the moment, the current on the secondary side of the first current transformer T1 is increased, the base voltage applied to the first triode VT1 is increased, the first triode VT1 and the third triode VT3 are enabled to be in a saturated conducting state, the second triode VT2 is cut off, the coil of the relay K loses power, the normally open switch of the relay K is released, the coil KM2 loses power successively, the second normally open contact KM3 is released, the first normally open contact KM1 is disconnected, the three phases stop supplying power to the alternating current motor M, and the effect of protecting the alternating current motor M is effectively achieved.

The emitter coupled bistable circuit has two stable states, is triggered by the amplitude of a signal, and is in one stable state when a voltage signal after voltage division is smaller than the rated voltage value of the alternating current motor M; when the voltage signal after voltage division is greater than the rated voltage value of the alternating current motor M, the circuit is in another stable state; the two states are changed at a very high speed, and other switch circuits can be reliably triggered after the two states are stable, so that the relay switch can be quickly cut off under the overcurrent condition, a power supply line is cut off, and the alternating current motor M is protected.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, a plurality of improvements and decorations can be made without departing from the technical principle of the present invention, and these improvements and decorations should also be regarded as the protection scope of the present invention.

Claims

1. The utility model provides an overcurrent protection circuit of three-phase motor which characterized in that: the overcurrent protection circuit comprises a main circuit and an overcurrent protection circuit;

the main circuit comprises a low-voltage circuit breaker (QF), a first normally open contact (KM1), a first phase line (A), a second phase line (B), a third phase line (C) and a three-phase motor (M), wherein the first phase line (A), the second phase line (B) and the third phase line (C) are respectively connected to the three-phase motor (M) through the voltage circuit breaker (QF) and the first normally open contact (KM 1);

the overcurrent protection circuit comprises a transfer Switch (STP), a control Switch (ST), a relay (K), a second normally open contact (KM3), a first current transformer (T1), a second current transformer (T2), a potentiometer (RP), a first triode (VT1), a second triode (VT2), a third triode (VT3) and a fourth triode (VT4), wherein the first end of the transfer Switch (STP) is connected to the second phase line (B), the normally open contact of the relay (K) and the second normally open contact (KM3) are connected in series and then connected in parallel with the control Switch (ST), and the second end of the transfer Switch (STP) is connected with the primary side of the second current transformer (T2) through a parallel circuit;

a primary side of the first current transformer (T1) is connected in series to the third phase line (C), a secondary side of the first current transformer (T1) is connected to a base of the first transistor (VT1) and a base of the third transistor (VT3) through the potentiometer (RP), a first diode (VD1) for rectification is connected between the secondary side of the first current transformer (T1) and a first end of the potentiometer (RP), a second end of the potentiometer (RP) is connected to a base of the first transistor (VT1), a third end of the potentiometer (RP) is connected in series to a first resistor (R1) for voltage division, an emitter of the first transistor (VT1) is connected to a collector of the third transistor (VT3), an emitter of the third transistor (VT3) is grounded, and a first end of a secondary side of the second current transformer (T2) is connected to a coil of the relay (K) through a fourth diode (VD4) and a coil of the relay (K) respectively The collector of the second triode (VT2) and the collector of the fourth triode (VT4), the emitter of the fourth triode (VT4) is grounded, and the base of the fourth triode (VT4) is connected with the cathode of the second diode (VD 2).

2. The overcurrent protection circuit for a three-phase motor according to claim 1, wherein: the overcurrent protection circuit further comprises a first capacitor (C1), a second capacitor (C2), a third diode (VD3), a fifth diode (VD5), a sixth diode (VD6), a second resistor (R2), a third resistor (R3), a fourth resistor (R4) and a fifth resistor (R5), wherein the anode of the first capacitor (C1) and the cathode of the first diode (VD1) are connected, the cathode of the first capacitor (C1) is grounded, the second resistor (R2) and the sixth diode (VD6) are connected in series between the second end of the potentiometer (RP) and the base of the first triode (VT1), the third diode (VD3) is connected between the emitter of the first triode (VT1) and the collector of the third triode (VT3), the third resistor (R3) and the fourth resistor (R5965) are connected in parallel between the base of the fourth diode (VD4) and the cathode of the second triode (VD 57324), the second capacitor (C2) and the fifth resistor (R5) are connected in series between the cathode of the second diode (VD2) and the base of the fourth triode (VT4), the cathode of the fifth diode (VD5) is connected with the base of the fourth triode (VT4), and the anode of the fifth diode (VD5) is grounded.

3. The overcurrent protection circuit for a three-phase motor according to claim 1, wherein: the first triode (VT1), the second triode (VT2) and the third triode (VT3) form an emitter-coupled bistable circuit.

4. The overcurrent protection circuit for a three-phase motor according to claim 1, wherein: further comprising a Fuse (FU) and a coil (KM2), the second current transformer (T2) is connected to form a loop by the Fuse (FU) and the first phase line (A), and the coil (KM2) is connected between a parallel circuit and the second current transformer (T2).

5. The overcurrent protection circuit for a three-phase motor according to claim 1, wherein: the first triode (VT1), the second triode (VT2), the third triode (VT3) and the fourth triode (VT4) are NPN type triodes respectively.

6. The overcurrent protection circuit for the three-phase motor according to claim 2, wherein: the first capacitor (C1) is connected in parallel between the first terminal of the potentiometer (RP) and the first resistor (R1) and used for storing the current on the secondary side of the first current transformer (T1), and the second capacitor (C2) is connected in parallel between the negative pole of the second diode (VD2) and the base of the fourth triode (VT4) and used for storing the current on the secondary side of the second current transformer (T2).

7. The overcurrent protection circuit for the three-phase motor according to claim 3, wherein: the emitter coupled bistable circuit comprises two states, the first current transformer (T1) outputs current through a secondary side, the potentiometer (RP) and the first resistor (R1) divide the voltage to form a voltage signal, the voltage signal is input to the base electrode of the first triode (VT1), when the voltage signal is smaller than a rated voltage value, the overcurrent protection circuit is in a state that the first triode (VT1) is cut off, and the second triode (VT2) and the third triode (VT3) are in a saturated conduction state; when the voltage signal is larger than the rated voltage value, the overcurrent protection circuit is in a saturated conduction state of the first triode (VT1) and the third triode (VT3), and the second triode (VT2) is in a cut-off state.