SU1274062A1 - Device for protection of three-phase electric motor against non-symmetric modes of operation - Google Patents

Abstract

The invention relates to the field of electrical engineering - relay protection of electrical installations from emergency operation and can be used to protect an electric motor and generator against overload and violation of the symmetry of the supply voltage. The purpose of the invention is to improve reliability by

Description

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prevent false triggering. The device contains current sensors 3,4 installed in the supply phases of the electric motor j to the output of which the relay coils on reed switches 5,6 are connected. The input of the filter 1 voltage reverse sequence is connected to the phases of the mains. To the output of the negative-sequence voltage filter 1, a threshold element is connected, made as an analog of a dynistor with an automatically controlled response voltage depending on the size of the engine load. To do this, a phase meter 11 is additionally introduced into the device, the output of which is loaded by two optocouplers 12 and 13, the photoresistors of which shunt the emitter transitions of the transistors 14 and 15 that perform the function of a dynistor analog. Phase meter 11 contains two comparators 19 and 20, four logic elements 2И-НЕ 21, 22, 23, 24, integrator 25, repeater 26, capacitor 27, resistor 28 and key 29. I 3. n, f-ly, 2 ill.

The invention relates to electrical engineering, namely, to force electric motors from asymmetry to stresses and to an increase in current in phases during overloads, and can be used to protect vehicle generators.

The purpose of the invention is to increase the reliability of the device by preventing the device from a false triggering when the load of a three-phase electric motor is not nominal.

FIG. 1 is a schematic diagram of the device; in fig. 2 -. schedule of comparators.

The device contains a negative sequence voltage filter 1, the inputs of which are connected to the power network supplying electric motor 2. Two phases of electric motor 2 are equipped with transformers 3 and 4 currents loaded by relay windings with reed switches 5 and 6 contacts of reed switches bypassing the reverse sequence voltage filter 1 . To the output of the filter 1 voltage reverse order. A filter capacitor 8 and a discharge resistor 9 are connected to the output of the filter 1 through the rectifier 7, to the output of the current transformer 4 and to the phase wire 10, the break of which includes a 4-current transformer, a phase meter 11 connected to the microcircuits. The output of the phase meter is loaded with LEDs of optocouplers 12 and 13, the photoresistors of which shunt the emitter transitions of transistors 14 and 15,

emitting an analogue of a dynistor, shunted by a capacitor 16. Accumulator capacitor 8 through transisors 14 and 15 is connected to performing element 17, which controls the operation of the magnetic actuator 18,

Phase meter 11 contains two comparators 19 and 20, four logic elements 2I-HE 21-24, an integrator 25, an analog memory cell made on a repeater 26, a capacitor 27, a resistor 28 and a switch 29.

The device works in the following way.

Claims (2)

After turning on the magnetic starter 18, a current flows through the power circuits of the electric motor 2. At the same time, the secondary current of transformer 3 and 4 is not sufficient for closing reed switches 5 and 6. When the supply voltage to the filter 1 is symmetrical, there is an unbalance voltage on the filter 1, to which the capacitor 8 is charged. transistors 14 and 15 of different structure, therefore, changes in the operation of the device does not occur. A prolonged asymmetry of the supply voltage at that power consumption leads to an increase in the voltage at the output of the filter 1. With a time delay, the capacitor 8 is charged to the amplitude value of the negative-sequence voltage. As soon as this value reaches the trigger voltage of the analog of the dynistor, filled with transistors 14 and 15, the capacitor 8 is discharged to the actuating element 17, the contacts of which disconnect the starter 18, stopping the motor 2. However, for motors with a working machine having a fan characteristic, for example, submersible pumps, when an asymmetrical mode occurs due to an increase in slip, a decrease in power consumption (decrease in the load factor) occurs, therefore such engines can continuously work with another higher unbalance factor. Therefore, it is necessary to increase the trigger voltage of the threshold element - dynistor. To this end, the emitter transitions of the transistors are shunted by photoresistors of optocouplers. The resistance of the resistors varies with the magnitude of the load factor of the motor, which can be judged by the magnitude of the shear angle between current and voltage. As the load factor decreases, the phase shift angle between the current and the voltage increases - (30 and 31 of Fig. 2). Using comparators 19 and 20, rectangular pulses are received (curves 32 and 33, Fig. 2). Logic elements 2I-HE 21-24 convert two input signals into rectangular pulses, the width of which is proportional to the phase angle between current and voltage ( curve 34, fig. 2). Using the integrator performed on the operational amplifier 25, the received pulses are integrated (curve 35, fig. 2), and the analog memory cell changes the voltage at the output of the phase meter (curve 36, fig.2). The device works when the phase angle changes from 0 to 90 °. An increase in voltage at the output of the phase meter 11 leads to an increase in the flux of photoresistors. This, in turn, leads to a decrease in the resistance of the photoresistors of optocouplers and an increase in the voltage of the analog of the dynistor. In order to avoid false triggering at high voltage rise rates, the analog of the dynistor is shunted by capacitor 16. Since the threshold voltage value of the analog of the dynistor has changed in accordance with the loading coefficient of the dvngatel, the device for protecting the three-phase electric motor from asymmetry of the supply voltages will work for another, higher the value of the asymmetry coefficient, thereby eliminating the false alarms of the device at low loads. The technical and economic efficiency of using the device is to reduce the number of false positives during non-nominal loads on the shaft, which leads to a reduction in technological damage. 1. Device for protection of a three-phase electric motor from an asymmetrical mode, containing a resistance-voltage reverse-sequence 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 current transformers, and the contacts shunt the filter resistors, the rectifying bridge connected to the output of the filter of the negative-sequence voltage, the storage capacitor with p An impedance connected to the output of the rectifying bridge, a capacitor and an actuator, characterized in that, in order to increase reliability by preventing the device from malfunctioning under non-nominal loads of a three-phase electric motor, it is additionally equipped with a phase meter connected to a current transformer and a phase wire, two bipolar transistors of different structure and two optocouplers connected to the output of the phase meter, and the photoresistors of the optocouplers shunt the emitter transitions ranzistorov included on analog circuit dynistor shunted and the second capacitor, and an actuator coil is connected to a storage capacitor through analog dynistor. 2. The device according to claim 1, wherein the phase meter contains two comparators, four logic elements 2I-NOT, an integrator and an analog memory cell, and $ 12740626 The inputs of the comparators are connected to the NAND trans element, the integrator and the current analogue analogue and the phase wire, and the memory cell is connected to the control circuit of their outputs through the logic optocoupler circuit. Thresholds Comparator L 35 36 Fig 2