CN112564045A

CN112564045A - Three-phase motor protector

Info

Publication number: CN112564045A
Application number: CN202011585168.5A
Authority: CN
Inventors: 吴华凯; 吴峰
Original assignee: Wenling Wuhua Electromechanical Co ltd
Current assignee: Wenling Wuhua Electromechanical Co ltd
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-03-26

Abstract

The invention relates to a three-phase motor protector, which comprises a current detection circuit for detecting the current on each phase line and a microprocessor; the output end of the current detection circuit is connected with the microprocessor; the switch control circuit controls the switch on each phase line to be disconnected at the same time, and is connected with the microprocessor. In the invention, the current condition entering each phase of the three-phase motor is detected by the current detection circuit, and the skilled person knows whether the microprocessor judges whether the phase is short, the current is balanced, whether the voltage is overloaded or not, and once the condition exists, the power supply of the motor is immediately turned off to protect the motor, and the power supply cannot be turned off only when the motor is heated.

Description

Three-phase motor protector

Technical Field

The invention relates to the field of three-phase motors, in particular to a three-phase motor protector.

Background

Distributing power in three phases is a common method of power transmission. Three-phase power systems use three Alternating Current (AC) voltage sources that are each 120 degrees apart in phase. In a balanced three-phase power system, three power supply lines carry three AC signals of the same frequency (and therefore the same period), which reach their instantaneous peak values at different times. With the current carried by one of the three power lines as a reference, the other two currents are delayed in time by 1/3 and 2/3, respectively, of one cycle of current.

One common way to generate three AC voltage sources is to construct an AC generator/alternator in which the rotating magnetic field is passed through three sets of wire windings, each set being 120 degrees apart around the circumference of the generator/alternator. Phase voltage refers to the amount of voltage measured across any one AC voltage source, such as a set of wire windings in an AC generator/alternator. Three-phase electrical power may be used to power motors and many other devices. For example, three-phase electrical power may be used to power a hermetic compressor motor, such as a motor in a reciprocating compressor.

The motor (motor) powered by a three-phase four-wire system power supply is a three-phase motor, and when the three-phase motor works, a danger can be caused if the motor is in phase failure, overloaded or unbalanced. At present, a motor protector is used for protecting a motor in the aspect of motor heating, but the service life of the motor can be influenced by frequent heating.

Disclosure of Invention

The invention provides a three-phase motor protector, aiming at protecting a motor in the aspect that the motor is often heated by the conventional three-phase motor protector, but the service life of the motor is possibly influenced by frequent heating.

The technical scheme of the invention is as follows: a three-phase motor protector comprises a current detection circuit for detecting the current on each phase line and a microprocessor; the output end of the current detection circuit is connected with the microprocessor; the switch control circuit controls the switch on each phase line to be disconnected at the same time, and is connected with the microprocessor.

Further, in the three-phase motor protector described above: the current detection circuit comprises a current transformer L for acquiring current on the phase line, and the output signal of the transformer L is amplified and then connected with a corresponding interface of the microprocessor.

Further, in the three-phase motor protector described above: the switch is a relay arranged on the phase line, the switch control circuit comprises a switch tube arranged on a relay coil power supply loop, and the control signal input end of the switch tube is connected with the corresponding port of the microprocessor.

In the invention, the current condition entering each phase of the three-phase motor is detected by the current detection circuit, and the technicians in the field know whether the microprocessor judges whether the phase is short, the current is balanced or not and whether the microprocessor is overloaded or not, and once the condition exists, the power supply of the motor is immediately turned off to protect the motor, and the power supply cannot be turned off until the motor is heated.

In addition, the mutual inductor is adopted to measure the current of the phase line, and the mutual inductor does not need to be connected to the phase line in series. And the adopted switch control circuit controls the three switches to be switched off simultaneously by one signal of the microprocessor, so that pins of the microprocessor are saved.

In addition, the invention is also provided with a detection circuit for detecting the phase voltage of each phase, the output of the phase voltage detection circuit is connected with the microprocessor, and if the phase voltage is lower than a set value, the power is cut off to protect the motor when the phase voltage is the same.

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Drawings

FIG. 1 is a schematic view of the motor protector detection and control points of the present invention.

Fig. 2 is a schematic block diagram of a motor controller according to the present invention.

Fig. 3 is a schematic diagram of a current sensing circuit of the present invention.

Fig. 4 is a schematic diagram of a switch control circuit of the present invention.

Detailed Description

As shown in fig. 1 and 2, the present embodiment is a three-phase motor protector, in practice, the three-phase motor (motor) protector of the present embodiment may be disposed in a control box of a motor, an input terminal of a three-phase four-wire industrial power supply is disposed in the control box of the motor at present, U, V, W and a zero line of the industrial power supply are respectively connected to four terminals on the control box to supply power to the motor, the motor protector of the present embodiment is disposed on a circuit board in the control box, and includes a current detection circuit for detecting a current on each phase wire and a microprocessor; the output end of the current detection circuit is connected with the microprocessor; the switch control circuit controls the switches on the phase lines to be disconnected simultaneously, and is connected with the microprocessor.

In this embodiment, the current detection circuit includes three independent detection circuits, each detection circuit detects U, V, W three phases, each detection circuit includes a U-phase current detection circuit, a V-phase current detection circuit, and a W-phase circuit detection circuit, in this embodiment, a current transformer L is used to collect the current on the phase line, as shown in fig. 3, the output signal of the current transformer L is amplified, the adopted circuits include an amplifier LM358, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a resistor R8, a capacitor C1 and a capacitor C2, a working power supply VCC, first, one end of the transformer L is grounded and connected in parallel with the resistor R3, the resistor R4 and the resistor R5 are connected in series between the working power supply VCC and ground, a capacitor C1 is connected between a common end of the other end of the transformer L connected with one end of the resistor R3 and a common end of the resistor R4 connected with the resistor R5, a common end of the resistor R4 connected in series with the resistor R5 and a positive phase resistor LM 6, the resistor R7 is connected in series with the capacitor C2 between the inverting input of the amplifier LM358 and ground, and the resistor R8 is disposed between the inverting input and the output of the amplifier LM 358. The current induced by the transformer L is amplified and then enters the microprocessor, the microprocessor performs AD conversion to form a digital signal, when the currents of the three phase lines are all converted into the digital signal, a person skilled in the art can use a proper computer program to realize comparison of the three digital signals, if one phase is detected, that is, the current of one phase is close to zero, the phase is detected to be absent, the power supply protection motor must be immediately disconnected, and when one phase of current is much larger or smaller than the currents of the other two phases, for example, the current of the V-phase is substantially the same as the current of the U-phase, but the current of the W-phase is 1.5 times or 75% of the current of the U-phase and the current of the V-phase, the current imbalance can be determined, and the motor must be immediately controlled to be powered off. In addition, if the three-phase currents are all larger than the set value, the overload is indicated, and the motor must be immediately powered off in order to protect the motor.

In addition, in this embodiment, a phase voltage detection circuit for detecting voltages of each phase is also provided, the circuit adopts a voltage division mode commonly used in the art, and uses a group of voltage division resistors to output phase voltages in proportion, for example, two resistors are connected in series and then grounded, a large resistor 30M and a small resistor 300K are connected in series and grounded, and a common end connecting the two resistors is connected, and then rectification and filtering are performed to form a direct current signal, because the phase voltage is generally 380VDC, 4-5V direct current can be formed under normal conditions after voltage division, when the voltage is less than 3V, it can be considered as low voltage, protection is required, power failure is controlled, and simultaneously, three-phase power failure occurs.

In this embodiment, the switch control circuit is shown in fig. 4, and is a switch control circuit that the MCU controls three switches to be turned off simultaneously, the circuit includes a switching transistor controlled by the MCU, such as a MOS transistor and a triode, in this embodiment, a triode Q1 is used, and in this embodiment, the switches used are relays K1, K2, and K3 that respectively control on/off of U, V, W three-phase lines, in other cases. Other controllable switches can also be used, the windings of the three relays are connected in series, each winding is connected with a diode in parallel, as shown in fig. 4, the diode D1, the diode D2 and the diode D3 are connected with two ends of the windings of the relays K1, K2 and K3 in parallel, the N pole of the diode is connected with the working power supply 12VDC, one end of the diode is connected with the working power supply of 12V, the other end of the diode is connected with the collector of the triode Q1, the emitter of the triode Q1 is grounded, the base of the triode Q1 is connected with the MCU through the resistor R1, and the base of the triode is. When the control signal generated by the MCU is active, that is, when the MCU determines that the three-phase power has the following conditions: lack the looks, overload, when unbalanced, a low level signal of telecommunication that will produce gives the switch tube, also be exactly triode Q1 cuts, at this moment, all there is not the electric current on the winding of three relay, then three relay all breaks off, accomplish the power-off protection to the motor, after reseing, the control signal that MCU produced is the high level, the control triode switches on, then the equal actuation of three relay, this moment, industrial three-phase current is to the motor power supply, at this moment, continue to monitor, also be exactly each phase current of real-time detection, if there is unusual (lack the looks, unbalance, overload) again, the relay disconnection is controlled.

Claims

1. A three-phase motor protector characterized in that: the device comprises a current detection circuit for detecting the current on each phase line and a microprocessor; the output end of the current detection circuit is connected with the microprocessor; the switch control circuit controls the switch on each phase line to be disconnected at the same time, and is connected with the microprocessor.

2. The three-phase motor protector of claim 1, wherein: the current detection circuit comprises a current transformer L for acquiring current on the phase line, and the output signal of the transformer L is amplified and then connected with a corresponding interface of the microprocessor.

3. The three-phase motor protector of claim 1, wherein: the switch is a relay arranged on the phase line, the switch control circuit comprises a switch tube arranged on a relay coil power supply loop, and the control signal input end of the switch tube is connected with the corresponding port of the microprocessor.