RU2300836C1 - Three-phase motor unbalance protection device - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed device that has resistor-capacitor reverse-sequence voltage filter, three-phase power supply, two current transformers, two reed relays, rectifier bridge, storage capacitor with discharge resistor, capacitor, final element, phase-meter, two different-structure bipolar transistors, and two optocouplers is provided with newly introduced push-buttons inserted in reverse-sequence voltage filter arms and connected in parallel with one of resistors.

EFFECT: enhanced reliability of three-phase motor protection against unbalanced operation.

1 cl, 2 dwg

Description

The invention relates to electrical engineering - relay protection of an electrical installation from emergency mode, and can be used to protect the electric motor and generator from overload and violation of the symmetry of the supply voltage.

The closest in technical essence is a device for protecting a three-phase electric motor from an asymmetric mode [1], containing a resistive-capacitive negative-sequence voltage filter connected to a three-phase network source, two current transformers connected to two phase wires, two reed relays, the windings of which are connected to the secondary windings of current transformers, and the contacts shunt the filter resistors, a rectifier bridge connected to the output of the voltage filter of the negative sequence, n a storage capacitor with a discharge resistance connected to the output of the rectifier bridge, a capacitor and an actuator, a phase meter, connected to a current transformer and a phase wire, two bipolar transistors of different structures and two optocouplers connected to the output of the phase meter, and the photoconductors of the optocouplers bypass the emitter junctions of the transistors included according to the circuit of an analog of a dynistor and shunted by a second capacitor, and the winding of the actuating element is connected to the storage capacitor through dinistor analog. The phasometer contains two comparators, 2I-NOT, an integrator and an analog memory cell, and the outputs of the compensators are connected to a current transformer and a phase wire, and their outputs through four logic elements 2I-NOT, an integrator and an analog memory cell to the optocoupler control circuit.

The disadvantage of this device is the failure of the device in case of problems inside it.

The present invention solves the problem of increasing the reliability of protecting a three-phase motor from an asymmetric mode.

To achieve this technical result, in a device for protecting a three-phase electric motor from unbalanced mode, which contains a negative-voltage resistive-capacitive voltage filter connected to a three-phase network source, two current transformers included in two phase wires, two reed relays, the windings of which are connected to the secondary windings of the transformers current, and the contacts are shunted by the filter resistors, a rectifier bridge connected to the output of the negative sequence voltage filter output, the drive a capacitor with discharge resistance connected to the output of the rectifier bridge, a capacitor and an actuator, a phase meter, connected to a current transformer and a phase wire, two bipolar transistors of different structures and two optocouplers connected to the output of the phase meter, and the photoconductors of the optocouplers bypass the emitter junctions of the transistors included according to the circuit of an analog of a dynistor and shunted by a second capacitor, and the winding of the actuating element is connected to the storage capacitor through an analog of d Nistor in button apparatus further incorporated in shoulders negative sequence voltage filter parallel to one of resistors. The phasometer contains two comparators, 2I-NOT, an integrator and an analog memory cell, and the outputs of the compensators are connected to a current transformer and a phase wire, and their outputs through four logic elements 2I-NOT, an integrator and an analog memory cell to the optocoupler control circuit.

The invention is illustrated in figures 1 and 2. Figure 1 shows a schematic diagram of a device. Figure 2 shows the thresholds of the comparators.

The device contains a reverse sequence voltage filter 1, consisting of two pairs of resistors and two capacitors, the inputs of which are connected to a power network supplying electric motor 2. Current transformers 3 and 4 are installed in two phases of electric motor 2, loaded with windings of reed relays 5 and 6. Reed contacts relays 5 and 6 bypass one of the resistors of the negative sequence voltage filter 1. In parallel with other resistors of the negative sequence voltage filter 1, buttons 7 and 8 are connected. To the output of the negative sequence voltage filter 1, a storage capacitor 10 and a discharge resistor 11 are connected through a rectifier 9. To the output of the current transformer 4 and phase wire 12, into the gap of which the current transformer 4 is connected connected phasometer 13, made on chips. The output of the phasometer 13 is loaded with optocoupler LEDs 14 and 15, the photoresistors of which are shunting the emitter junctions of transistors 16 and 17, which form an analog of a dynistor, shunted by a capacitor 18. The storage capacitor 10 is connected through transistors 16 and 17 to an actuating element 19 that controls the operation of the magnetic starter with contacts 20.

The phasometer 13 contains two comparators 21 and 22, four logic elements 2I-NOT 23-26, an integrator 27, an analog memory cell made on a repeater 28, a capacitor 29, a resistor 30, and a key 31.

The device operates as follows.

After the magnetic starter 20 is turned on, current flows through the power circuits of the electric motor 2. In this case, the secondary current value of transformer 3 and 4 is insufficient to close the reed relays 5 and 6. With a symmetrical supply voltage at the output of filter 1 of the negative sequence voltage, there is an unbalance voltage to which capacitor 10 is charged. The magnitude of this voltage is insufficient to open the analog of the dynistor made on transistors 16 and 17 of different structures, therefore, changes in the operation of the device does not occur.

Long asymmetry of the supply voltage at that power consumption leads to an increase in the voltage at the output of the filter 1 voltage of the negative sequence. With a time delay, the capacitor 8 is charged to the amplitude value of the voltage of the negative sequence. As soon as this value reaches the operating voltage of the analog of the dinistor made on transistors 16 and 17, the capacitor 18 is discharged to the actuator 19, the contacts of which disconnect the magnetic starter with contacts 20, stopping the motor 2. The same thing happens when checking by clamping one of the buttons 7 or 8.

However, for engines with a working machine having a fan characteristic, for example, submersible pumps, when an asymmetric mode occurs due to an increase in slip, a decrease in power consumption (decrease in load factor) occurs, therefore, such engines can operate for a long time with another, higher value of the asymmetry coefficient. Therefore, it is necessary to increase the response voltage of the threshold element - the analog of the dinistor.

For this purpose, the emitter junctions of transistors are shunted by optocoupler photoresistors. The resistance of the resistors varies depending on the load factor of the motor, which can be judged depending on the magnitude of the angle of shear between current and voltage. With a decrease in the load factor, the phase angle between the current and voltage increases (curves 1 and 2, Fig. 2). Using comparators 21 and 22, rectangular pulses are obtained (curves 3 and 4, FIG. 2). Logic elements 2I-NOT 23-26 convert two input signals into rectangular pulses, the width of which is proportional to the angle of the phase shift between current and voltage (curve 5, Fig.2). Using the integrator performed on the operational amplifier 27, the obtained pulses are integrated (curve 6, FIG. 2), and the analog memory cell, made on the repeater 28, carries out a voltage change (curve 7, FIG. 2). The device works when changing the angle from 0 to 90 °.

An increase in the voltage at the output of the phase meter 13 leads to an increase in the flux of illumination of the photoconductor optocouplers 14 and 15 and to an increase in the response voltage of the analog of the dynistor. To avoid false triggering at high voltage rise rates, the analog of the dinistor is shunted by the capacitor 18. Since the threshold voltage of the analog of the dinistor has changed in accordance with the engine load factor, the device for protecting a three-phase electric motor from asymmetry of the supply voltage will work with another, higher value of the asymmetry coefficient, thereby eliminating false alarms of the device at low loads.

The source of information

1. A.S. USSR No. 1274062, Н02Н 7/08, 1986, B No. 44 - prototype.

Claims (1)

A device for protecting a three-phase electric motor from an asymmetric mode, comprising a negative-sequence resistive-capacitive voltage filter connected to a three-phase network source, two current transformers included in two phase wires, two reed relays, the windings of which are connected to the secondary windings of the current transformers, and the contacts are shunted filter resistors, a rectifier bridge connected to the output of the reverse sequence voltage filter, a storage capacitor with a discharge resistance, connected to the output of the rectifier bridge, a capacitor and an actuator, the device is equipped with a phase meter connected to a current transformer and a phase wire, two bipolar transistors of different structures and two optocouplers connected to the output of the phase meter, and the photoconductors of the optocouplers bypass the emitter junctions of the transistors connected according to the analogue transistor circuit and shunted by the second capacitor, and the winding of the actuating element is connected to the storage capacitor through an analog of a dynistor, distinguishing This is due to the fact that buttons are added to the device, shunting resistors in the negative sequence voltage filter.

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