SU1314288A1 - Method of checking non-uniformity of air gap of induction squirrel-cage rotor motor - Google Patents

Abstract

The invention relates to methods for controlling the amount of uneven air gap in an asynchronous motor with a short-circuited rotor. The purpose of the invention is to improve measurement accuracy. The electric motor idling is accelerated to the nominal speed of rotation and an electrical signal is measured proportional to the magnitude of the air gap non-uniformity. As an electrical signal proportional to the magnitude of the air gap, rms of even harmonics is used, which are separated from the current curve flowing through the motor winding. The method allows to reduce labor costs in determining the size of the air gap non-uniformity. 1 il. (L oo 1 IND 00 oo

Description

The invention relates to electrical engineering, and more specifically to electrical engineering, and can be used to control the magnitude of the air gap unevenness (eccentricity) in asynchronous motors with a short-circuited rotor during their assembly and testing.

The purpose of the invention is to improve the measurement accuracy.

The drawing shows the experimentally measured calibration curve (solid line) of the root mean square value of even current harmonics (U) versus relative eccentricity (measured points of the eccentricity for the engine part are shown by dots).

The determination of the size of the air gap unevenness according to the proposed method is carried out as follows.

The electric motor idling is accelerated to the nominal rotational speed, after which even harmonics are filled with the curve of the current flowing through its windings and the root-mean-square value of them is calculated.

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As shown by experimental studies, the second harmonic is most clearly expressed;

the magnitude of the second harmonic of the AM current depends on the value of the eccentricity of the air gap;

the discrepancies between the calculated non-uniformity of the air gap, determined by the second harmonic, and the experimental values did not exceed 7%.

The proposed method (in comparison with the known method) reduces the labor costs of determining the size of the non-uniformity of the air gap and increases the accuracy of the measurement.

Claims (1)

Invention Formula The curve of the current flowing through the windings of an asynchronous electric motor has a non-sinusoidal shape when it is powered from a sinusoidal voltage source, and the presence of even harmonics is caused only by the unevenness of the air gap. The degree of unevenness in the air gap is proportional to the mean square of the 40th harmonic value of the apparent even harmonics in the curve of the current flowing through the motor windings. The method can be implemented using well-known technical means, 45 for example, the selection of even harmonics can be performed using resonant filters, and the calculation of the root-mean-square value can be performed using thermal or electromagnetic measuring devices. Example. For testing from a batch of induction motors, type 4А80В143, a motor with a practically uniform air gap was selected (measurements using probes, as well as by the even harmonics of the current, showed that it was close to zero). To obtain a given non-uniformity The method of controlling the air gap non-uniformity of an asynchronous squirrel-cage motor, which consists in accelerating the engine at idle, extracting harmonic components from the stator current, carrying information about the non-uniformity of the air gap, form a controlled signal proportional to the non-uniformity of the air gap, and by its difference from the signal of the set-point it is judged These air gaps were ground by locks for a certain amount of bearings for a certain amount, after which the engine was accelerated by using the 5-harmonic analyzer SCF-56 to measure even-harmonic currents. The measurement results are shown in the drawing as a solid curve. The nominal air gap of the engine is 0.5 mm. JO, where f is the absolute value of the eccentricity (in mm). The voltage values U are given for the second harmonic .; S The remaining engines of the test batch were accelerated at idle and the second harmonic value in the stator current was measured by a harmonic analyzer. The resulting value (points not 20 drawing) was compared with a calibration curve, as a result of which the magnitude of the rotor eccentricity was determined. The gap was controlled with a probe through drilled holes in the side holes. In this way: in the curve of the stator current HELL, even harmonics appear when the air gap is not uniform, 45 50 The method of controlling the air gap non-uniformity of an asynchronous squirrel-cage motor, which consists in accelerating the engine at idle, extracting harmonic components from the stator current, carrying information about the non-uniformity of the air gap, form a controlled signal proportional to the unevenness of the air gap, and by its difference from the setpoint signal, the magnitude of the unevenness of the air gap is judged, in order to improve the measurement accuracy, they are separated from the stator current even harmonics, and the monitored signal form in proportion to the rms amplitude of the amplified even current harmonics. Editor A.Revin Compiled by A.Treputnev Tehred V. Kadar Proofreader S. Cherni Order 2210/47. Circulation 731 Subscription VNIIPI State Committee. USSR for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab. 4/5  - -. “.-..------ --- - - - - --- ----- - - - - - - - Production and printing company, Uzhgorod, st. Project, 4