Research of electric machines with the help of light-emitting diodes. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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This article is dedicated to increasing visibility in electrical engineering, eradicating one common misconception. It will be useful to anyone involved in the study of electric motors and alternators.

The purpose of this study is to determine the phase shift angle obtained using an asynchronous motor (IM) operating as a single-phase to three-phase current converter. Such a "dynamo transformer" should provide a simplified start-up and operation of electric motors of a small enterprise (Fig. 1).

We were alarmed by the publications [1, 2], which stated that such a circuit solution gives a phase shift not by 120°, but by 90°. The same was repeated by textbooks on electrical engineering. We did not have a three-channel oscilloscope at hand, so we decided to make something similar based on LEDs.

First, we checked the performance of the circuit shown in Fig. 2 for a single-phase current on a motor 220/380 V (∆/λ), 1500 rpm (rounded).

All connections in the diagrams of this article should be made using a lamp phase indicator (Fig. 3) and observing safety rules.

A two-color LED of the ALS331A type (L93WEGC, LHG3392) was mounted on the motor shaft, which in subsequent experiments was replaced by less scarce LED pairs of red and green LEDs soldered to each other (Fig. 4).

One end of such a pair was attached to the shaft, the other - to the contact pad made of foil fiberglass glued to the end of the shaft (Fig. 5).

The phase voltage was applied to a running engine through a 100 kΩ resistor and a standard measuring probe. The resulting light-dynamic picture made it possible to determine the number of pole pairs inside the electric machine, as well as the slip. Sliding is determined by counting the revolutions of the light-dynamic pattern for a minute [3].

It became possible to determine the speed of rotation of the shaft (Fig. 6) and the load factor (the ratio between slip during the desired load and normal).

A segment of a strip of light of any one color (red or green) indicates not only one of the stator poles, but also the distance that a luminous LED travels in 0,01 s! When the engine was turned off, the diodes did not go out immediately, which clearly indicated that the IM was operating in the electric generator mode. The experiment showed the futility of regulating the speed of IM by changing the voltage. To do this, most often use a change in the number of poles, as well as the frequency of the supply current.

Thus, a light-dynamic picture was obtained for one phase. But we were interested in the spatial picture for all three phases of our engine-generator. To do this, it was necessary to isolate the body of the electric machine from the chassis (when the engine is powered from two phases (380 V), it is not necessary to isolate it) and connect it to the center of the "star", and scratch special annular grooves on a plate of foil fiberglass with a piece of hacksaw blade (Fig. 7) .

Two more pairs of LEDs and two resistors were added to the circuit. During engine operation, three voltages were applied to the indicator device using a set of contacts made of foil textolite and wire. On the case of a running engine, 127 V was formed relative to the mains voltage (with a two-phase supply of 0 V), which required the observance of appropriate safety measures. Regardless of the direction of rotation of the motor shaft, at a speed of 1500 rpm, we got the same picture (Fig. 8).

The colored stripes corresponded exactly to the windings in the motor stator. From the resulting light-dynamic picture, we concluded that the angle between the phases of our engine-generator is not 90°, but 120°.

References:

1. Yakovlev V.F. Three-phase electric motor in a single-phase network // Elektrik. 2001. - No. 12. - P.13.
2. Rashitov O.G. The use of a single-phase network to power a three-phase electric motor / / Elektrik. - 2002. No. 12. - C.3.
3. Ivanov A.A. Handbook of electrical engineering. - K., 1984. - P. 135.

Author: Y. Fenyak, Y. Bearded

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