RU2529596C1 - Method of diagnostics of turn-to-turn short circuits of asynchronous electric motor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: amplitudes of runout phase voltages and periods of oscillation of these voltages. These values are compared with the values recorded earlier for the serviceable electric motor. By the measured values falling outside the allowable range provisioned by an measurement errors and allowable deviation of measured parameters from initial values the occurrence of turn-to-turn failures can be witnessed.

EFFECT: diagnostics of turn-to-turn failures at an early stage of development.

5 dwg

Description

The invention relates to electrical engineering and is intended to detect interturn damage in the stator winding of an asynchronous electric motor.

A known method of functional diagnostics that controls the relationship of the total resistance of the windings for each pair of motor windings, i.e. asymmetry of the windings (see RF patent No. 2351048, IPC H02H 7/08, publ. 03/27/2009).

The disadvantage of this method is the low sensitivity to interturn closures, because they do not cause tangible changes in the currents consumed by the electric motor.

There is also known a method of protecting an induction motor from coil circuits, in which the instantaneous current values are calculated and compared with the registered values at the measured slip value (see RF patent No. 2297704, IPC H02H 7/08, published on 04/20/2007). In the calculation, the method of successive approximations is used, the calculation is carried out until the calculated current is not, with an acceptable error, close to the measured value, so, in series, the equivalent active resistance and equivalent inductance values are selected (with the measured slip value) and judged by them about the state of the electric motor.

The disadvantage of this method is the reduced accuracy due to the lack of consideration of possible phase imbalance.

A known method for diagnosing the technical condition of an electric motor according to its electrical parameters (see RF patent No. 2425391, IPC G01R 31/34, published on July 27, 2011). The essence of the method is to compare the spectrograms of power losses according to the measured parameters and similar spectrograms on a known-good engine.

The disadvantage of this method is the reduced accuracy due to the influence of network interference.

Closest to the claimed method is a method for diagnosing an electric motor, taken as a prototype (see RF patent No. 2193270, IPC H02K 15/00, G01R 31/34, published on November 20, 2002). The essence of the method is to control the EMF generated by an electric machine during inertia rotation when the supply voltage is turned off.

The disadvantage of this method is the low accuracy due to the lack of consideration of the frequency generated by the electric motor of the EMF.

The technical result of the invention is the creation of an effective and simple method for diagnosing the technical condition of asynchronous electric motors, including in remote conditions.

The result is achieved in that the method for diagnosing inter-turn faults of an induction motor, including measuring the EMF of the motor winding when the shaft rotates by inertia after turning off the supply voltage, differs in that they additionally measure the frequency of the EMF oscillations, compare these values with the values measured on a working motor, and the comparison results conclude that there are interturn closures.

The essence of the method is that at certain moments, after the start of the motor run-down, the amplitude values of the damped voltage fluctuations, as well as the current values of the period are measured at its terminals, then these values are compared with the values recorded on a known-good electric motor. With a difference in the values above the permissible level, a signal is generated indicating the presence of an inter-turn circuit and its scale, depending on how far the threshold is exceeded. The waveform in figure 2 shows the transient run-out of the electric motor when 20% of the winding is damaged, in figure 3 - 40% of the winding. Analysis of the processes on the coast is performed according to the values shown in the diagrams: Fig. 4 - dependence of the phase voltage amplitude of one winding of an induction motor on time from the start of coasting; Fig. 5 - change in the voltage period (converted to frequency) depending on the scale of the damage to the winding.

Figure 1 presents a block diagram of a device that implements the method.

The device contains a three-phase voltage network 220/380 - 1, a contactor - 2, three voltage sensors - 3, an asynchronous electric motor - 4, a microcontroller - 5, a keypad - 6, a voltage converter - 7, a display - 8.

The asynchronous electric motor 4 is powered by a three-phase voltage network 1, the electric motor is connected to the network by a contactor 2, after which three voltage sensors 3 are connected to the motor power line, in addition, the microcontroller 5 and the display 8 are fed through the voltage converter 7, the microcontroller 5, in turn receives data from the push-button keyboard for data input 6, from voltage sensors 3 and performs two-way, signal-blocking communication with the contactor, and also displays data on display 8.

The device operates as follows.

Before starting the device using the keypad 6 enter the microcontroller 5 settings the number of registered voltage measurements and the range of permissible deviations of the phase voltage.

When the motor 4, the device operates in standby mode. When the electric motor 4 is disconnected by the contactor 2 from the power source 1, the additional contactor contact opens, this signal is received by the microcontroller 5 via a signal-blocking connection, from this moment the microcontroller 5 starts to count down the time and when the phase voltage passes through the maximum (as determined by constant measurements of the analog voltage -digital converter of microcontroller 5 and comparison with previous values), microcontroller 5 registers the voltage values received from the sensor unit n conjugation 3, and records the time from the start of the previous maximum (the time interval between the peaks is considered the current value of the period - oscillations). The number of measurements of the voltage maximums is dictated by the accuracy sufficient for comparison with the values recorded on a previously operational electric motor. After registering a given number of values, the microcontroller 5 compares the measured voltages and current periods with the performance of a functioning electric motor. According to the deviation of the module of the difference between the measured voltage values and the periods of fluctuations from the allowable range entered before the device started to work, the user decides to carry out preventive work to limit or eliminate the causes of the development of inter-turn damage. In the event that the module of the difference in the measured values from the specified range, the microcontroller 5 blocks the contactor by switching on the signal-blocking connection, opening the contactor coil power circuit, and displays a blocking message on display 8.

The proposed method allows to detect inter-turn faults, while the network interference and distortion do not affect the diagnostic result, because All measurements are made on an electric motor disconnected from the network (source of interference) and rotating by inertia. The method also allows you to diagnose inaccessible electric motors without dismantling them, because for diagnostics, it is enough to have access to the motor terminals, which are located together with the switching equipment in the switchboard.

Claims (1)

A method for diagnosing inter-turn faults of an induction motor, including measuring the EMF of the motor winding when the shaft rotates by inertia after turning off the supply voltage, characterized in that they additionally measure the frequency of the EMF oscillations, compare these values with the values measured on a working motor, and conclude by the presence of interturn closures.

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