SU1555760A1 - Method of protection of submersible electric motor with two and more phase windings from abnormal operating conditions - Google Patents

Abstract

This invention relates to electrical engineering, in particular, to relay protection. The purpose of the invention is to increase the operational reliability and determine the cause of the abnormal mode. With a symmetric underload of the motor, the phase currents decrease, the variable voltages become less than a fixed value, and the number of pulses is zero. In the asymmetrical mode of the motor or phase failure, the phase currents have different meanings. Therefore, one of the voltages becomes less than a fixed value and the total number of pulses per cycle becomes less than during normal operation. In order to protect against non-stationary modes caused by load oscillations, for example, with cavitation phenomena in a pump, it is advisable to additionally compare the number of pulses in individual cycles and, by their difference, generate a signal to turn off the electric motor.

Description

The invention relates to electrical engineering and can be used in protection devices for submersible AC motors that are powered by a multiphase electrical network.

The purpose of the invention is to increase the operational reliability and determine the cause of the abnormal mode.

The drawing shows diagrams illustrating the proposed method.

The method is carried out as follows for an electric motor with three phase windings.

If, as electrical parameters, the phase currents of an electric motor are used, they are converted into alternating voltages Id, Us, Uc, proportional to these currents, and then into the total pulsating voltage U (diagram a). A constant fixed voltage level is set, against which the number of pulses n per cycle is measured (1c times the power supply circuit Tc (in the diagram a t,, 2 Tc).

In the case of a symmetric overload - the electric motor, the phase currents will increase and, accordingly, the variable loops UA, U & Uc form the total pulsating voltage U, the constant component of which will exceed FixiSd

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voltage U., and the number of pulses is 1 (diagram b).

With a symmetric underloading of the electric motor, the throttle phase currents decrease in ms, and the variable voltages UA, U6, Uc become less than a fixed value of U, and the number of pulses is zero (diagram c).

In the asymmetrical mode of the motor or phase failure, the phase currents have a different meaning. Therefore, one of the stresses, for example, U &, becomes less than a fixed value of U, (and the total number of pulses per cycle t becomes less than during normal operation (diagram g).

To protect against non-stationary modes caused by load fluctuations, such as cavitation phenomena and a pump, it is advisable to additionally make comparisons of the number of pulses in individual cycles and generate a signal to turn off the electric motor according to their difference (diagram e).

Improving the accuracy of protection will allow the use of several fixed and sound voltages Uo U2, against which the pulses are counted. In this case, it is possible to set the necessary limits separately for overload, underload and asymmetrical operation.

The number of pulses also serves as additional information about the cause of the abnormal mode for signaling.

Similarly, the method can be implemented for an electric motor with more than one phase winding.

If phase voltages are used as electrical parameters, the method allows the motor to be protected with increasing and decreasing voltages, asymmetries of phase voltages, including phase failure.

The described method is based on counting the number of pulses exceeding in level a fixed level of constant voltage in a pulsating voltage proportional to the phase voltage.

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electrical parameters, allows simple means to implement a comprehensive protection of the electric motor, i.e., increase operational reliability and determine the cause of the anomalous mode. The technical implementation of the device based on the invented method can be performed, for example, on the following elements: conversion of phase currents into alternating voltages by current sensors, conversion of alternating voltages into total pulsating with a three-phase rectifier, separation of pulses coinciding with a fixed level of constant voltage, by a dynistor or comparator, pulse counting and setting the cycle duration by pulse counters synchronized with the network frequency. Determining the cause of the abnormal mode and generating a trip signal is performed by a logic circuit on the elements or by a microprocessor.

Claims (2)

1. A method of protecting a submersible electric motor with two or more phase windings from anomalous modes, based on converting alternating voltages proportional to the electrical parameters of each phase into a total pulsating voltage, and generating a trip signal, characterized in that reliability and determine the cause of the anomalous mode “in a pulsating drop cyclically with a given cycle time, but not less than two periods of the current frequency of the supply network, counting The number of pulses exceeding the level of a fixed DC voltage level, the number of impulses in the cycles determine the cause of the abnormal mode and form a shutdown signal. 2. Method of claim 1, characterized in that the constant voltage level is set in the range from the constant component level to the maximum value of the pulsating voltage at the nominal operating conditions of the electric motor. and U A UB Uc -frwK  Y -frwK  Yp-in UA / Us, t / c U, tr 6 u, u, v mo