SU1224894A1 - Device for protection of three-phase motor against overload and phase loss - Google Patents

Abstract

The invention makes it possible to increase the sensitivity and reliability of a device for protecting a three-phase electric motor against overload and phase failure by eliminating false triggering during start-up mode. The device contains three measured transformers with 1, 2 and 3 with one primary winding. Transformers 1 and 3 each have one secondary winding 4 and 5, and transformer 2 has two secondary windings 6 and 7, and the number of turns in them is the same. One output of each of the secondary windings of transformer 2 is counter-connected to the output of the secondary winding 4 and 5 of transformers 1 and 3, respectively. The secondary windings of transformers 1 and 3 compared with the secondary windings of transformer 2 have a different number of turns. The remaining conclusions of the secondary windings of all transformers are connected to the element of control and comparison of overloads (EXPR) 8, made in the form of a phase-sensitive circuit, the output of which includes a disconnecting element 9, intended for switching the electric motor 10. 1 sludge. (Lu n3 4 00 (x 4

Description

one

The invention relates to :(; a line of three-phase electric motors, in which 1 o;) s, phase correlations of a three-phase network are used.

The aim of the invention is to iioBbiujeHae the sensitivity and reliability of the device by eliminating false triggering during start-up mode.

The drawing shows a diagram of the proposed device.

The device contains three measuring transformers 1, 2 and 3 with one primary winding, which are included in the three-phase power supply system of the electric motor.

Measuring current transformers 1 and 3 extreme phases each have one secondary winding 4 and 5, and the measuring transformer 2 of the middle phase has two secondary windings 6 and 7, One output of each of the two secondary windings of the measuring transformer 2 of the middle phase is oppositely connected to the corresponding secondary flow 4 and 5 transformers of extreme phases.

The remaining terminals of the secondary windings of all transformers are connected to the control element and compare overloads 8, the output of which is the disconnecting element 9, which is intended for switching the electric motor 10.

The element of control and comparison of overloads (EXP) is made in the form of a phase-sensitive circuit. In this element, both voltages Ui and U2 are compared with each other, and the value of one of them, for example, U | is matched with the set threshold of the device corresponding to an unacceptable overload of the motor. EXP also controls the angle of displacement between voltages U | and U.

If the voltage Ui exceeds the previously established permissible value and becomes higher than the response threshold, then, when triggered, the threshold element unbalances the phase-sensitive circuit and an unbalance signal appears that amplifies and arrives at the disconnecting element.

The device works as follows.

During normal operation, the motor voltage Ui and U-j are the same in magnitude, but shifted relative to each other by an angle of 90 °. The magnitude of the monitored voltage is lower than the tripping threshold voltage and there is no signal at the EXP output.

With the appearance of symmetric overloads, the magnitude of the voltages Lb and Us increases, and with an unacceptable overload these voltages become higher than the threshold of the device. When a threshold element is triggered, the equilibrium of the phase-sensitive cxeMi i is unbalanced and a signal appears at the input, which is fed to the disconnected element.

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With the break of one phase, the phase shift angle between the currents of the three-phase network changes, the shift angle between the voltages Ui and U2 also changes, the equality of the amplitude values of these values is violated, due to Hei o the balance of the phase-sensitive circuit is balanced is the signal that is triggered and the disconnecting element turns off the motor.

10 The device version allows you to create a dependent or playfully dependent time current response characteristic of a device and match this characteristic with the overload characteristic of an electric motor.

Thus, in the proposed device, the instrument current transformers have only one primary winding, which can be made in the form of a single turn, this allows a significant reduction in the size of the transformers.

In addition, since in the proposed device, a shift angle between voltages of 90 ° is formed in the secondary windings and is created by a certain number of turns using their respective

25 inclusions, it is structurally simple to pick up the necessary ratio of turns equal to 2.75, thereby ensuring the necessary reliability and sensitivity of the device.

Claims (1)

The invention of the device to protect the three-phase 30 motor overload and phase failure, containing two measuring current transformers, the primary windings of which with different numbers of turns are included in different phases of the motor, and the secondary ones are connected to the reference element, while the co3 ratio of the turns of the primary windings provides two voltages at the input of the comparison element, 90 ° phase-shifted overload control elements, responsive and off, characterized by 4Q by the fact that, in order to maintain reliability by eliminating false triggering during start-up mode, the indicated current transformers have one primary and one secondary winding each and a third measuring transformer with one primary and two secondary windings is additionally introduced. the number of turns, with one output each of the secondary windings of the third measuring transformer is counter-connected to the output of the secondary winding of the first and second measuring transformer, respectively The other B111 leads of the secondary windings of all measuring transformers are connected to the control element and compare overload, the secondary windings of the nopBOi o and the second measuring transformers compared to the secondary windings of the third measuring transformer once, the number of turns. 50