STUDY OF THE INFLUENCE OF THE MANUFACTURING PROCESS OF WINDINGS ON DEFECTS IN TURN INSULATION OF ASYNCHRONOUS MOTORS

Yu. P. Pokhodkov, P. P. Besperstov, V. V. Pykhtin

(Presented by the scientific seminar of the Department of Electrical Insulation and Cable Engineering)

The growth in the needs of the national economy for asynchronous motors for general industrial use makes it an urgent task to increase their output. The optimal way to solve this problem is the automation and mechanization of the technological processes of motor manufacture. One of the most labor-intensive operations in the manufacture of asynchronous motors is the laying of the winding into the stator slots. At present, at a number of electrical-machine-building plants, semiautomatic winding machines are used to mechanize this operation. The use of these machines, on the one hand, leads to a sharp increase in labor productivity, and on the other—to a deterioration in the quality of the turn insulation after the winding has been laid.

The studies of L. M. Bernstein [1] showed that, in the manufacture of sections and coils, elongation of PETV wire of diameter 1.62 mm can reach 6–8%, which leads to an increase in the number of surface cracks per centimeter of length from 25 to 47.

An analysis of failures of electrical machines in operation shows that a significant part of them occurs during the running-in period, mainly because of hidden defects in the insulation. The largest percentage of machine failures during the running-in period is attributable to turn insulation and amounts to 7–10% [2, 3].

Insulation failure can occur only when there is through damage in it. Consequently, it is expedient to use its defectiveness as a criterion of insulation quality [4].

In the present work an attempt is made to estimate the influence of fluctuations in the technological operating conditions of a WST-660 winding machine manufactured by “Elektromat” of the GDR on defects in turn insulation.

To solve the problem posed, it is necessary to develop a mathematical model of defect formation in turn insulation during the manufacture of windings, taking into account the quality of the insulation in the as-supplied state and the levels of the technological operating conditions of winding machines. Models are usually developed by setting up a classical or factorial experiment. In the classical approach, the number of experiments may prove inadmissibly large, and the results are presented in a form difficult to survey. Increased research efficiency is achieved by using mathematical methods of statistical factorial experimental design [5].

According to a priori information, the main factors exerting a substantial influence on defect formation in turn insulation duringיז in the visible end of the page.

in laying the winding on the winding machine are the wire tension force \((P)\) and the winding speed \((V)\). For these factors, an experiment was planned according to a central composite rotatable second-order design (Table 1).

Table 1

The nominal operating conditions of the winding machine, used at the Sibelektromotor plant when laying the winding into the slots of the stator core of the AO2-32-2 motor with wire of grade PETVØ0.96, were taken as the zero levels of the factors. The levels of the factors and the intervals of their variation are given in Table 2.

Table 2

After laying, the winding was carefully removed from the stator slots in order to prevent the introduction of additional defects. Then the winding was cut into specimens 125 mm long, which were tested for breakdown in “wire—shot” electrodes, the shot diameter being equal to the wire diameter. In carrying out one row of the design, 200 specimens were tested. From the magnitude of the breakdown voltage, the value of the defectiveness of the insulation of the wire [4] laid in the stator slots was determined for different operating conditions of the winding machine in accordance with the design. To assess the influence of the quality of the wire entering the plant on defect formation during manufacture of the winding, wires from three different batches were selected, characterized by different levels of defectiveness of the wire insulation:

\[ q_{1\mathrm{p}}=0{,}08;\quad q_{2\mathrm{p}}=0{,}15;\quad q_{3\mathrm{p}}=0{,}27. \]

As a result of carrying out the experiment and processing the data [5], equations were obtained in coded units, relating the defectiveness

turn insulation after laying the winding, with the winding speed and the wire tension force.

For \(q_{1\mathrm{p}}=0.08\)

\[ q_{1\mathrm{n}}=0.755+0.0473X_1+0.02X_2-0.0484X_1^2+0.0324X_2^2- \]
\[ -0.0275X_1X_2 . \tag{1} \]

For \(q_{2\mathrm{p}}=0.15\)

\[ q_{2\mathrm{n}}=0.775+0.05X_1+0.03X_2-0.0239X_1^2+0.0293X_2^2- \]
\[ -0.05X_1X_2 . \tag{2} \]

For \(q_{3\mathrm{p}}=0.27\)

\[ q_{3\mathrm{n}}=0.841+0.0335X_1+0.0302X_2-0.042X_1^2+0.0297X_2^2- \]
\[ -0.0325X_1X_2 . \tag{3} \]

Verification of adequacy by Fisher’s \(F\)-criterion at the 5% significance level showed that the equations obtained adequately describe the experimental results. The defectiveness values obtained from the results of calculations and experiments are given in Table 1.

After describing the corresponding coefficients as functions of the defectiveness of the wire in the as-supplied state [7] and replacing coded quantities by natural ones [6], we obtain a generalized model of defect formation in turn insulation when manufacturing the winding on a WS1-660 machine:

\[ q_{\mathrm{n}}=4.54\cdot10^{-5}\cdot q_{\mathrm{p}}^{-3.24}\cdot e^{19.63q_{\mathrm{p}}}+ \]
\[ +0.0168V- \tag{4} \]
\[ -1.54\cdot10^{-4}\cdot q_{\mathrm{p}}^{-2.64}\cdot e^{15.3q_{\mathrm{p}}}\cdot P- \]
\[ -4.98\cdot10^{-10}\cdot q_{\mathrm{p}}^{-3.88}\cdot e^{24.2q_{\mathrm{p}}}\cdot V^2+ \]
\[ +0.0621\cdot P^2- \]
\[ -15.75\cdot q_{\mathrm{p}}^{3.1}\cdot e^{-18.8q_{\mathrm{p}}}\cdot V\cdot P . \]

Equations (1–4) show that the operating modes of the winding machine have a substantial effect on the quality of the winding insulation. The use of the generalized equation makes it possible to approach, in a well-founded manner, the establishment of optimal operating modes of winding machines. By adjusting the operating modes, it is possible both to increase the productivity of the technological equipment and to improve the quality of the winding insulation.

Fig. 1. Lines of equal level of defectiveness of turn insulation: a) \(q_{\mathrm{p}}=0.27\); b) \(q_{\mathrm{p}}=0.08\)

Figure 1 shows lines of equal levels of defectiveness of turn insulation after winding placement for various defectivenesses of the wire insulation in the as-delivered condition. Analysis of the dependences shows that the operating regimes of the winding machine existing at the plant are optimal. The quality of the turn insulation of the winding cannot be substantially improved without reducing the productivity of the equipment. However, without reducing the quality of the turn insulation of the winding, the winding speed can be increased from 80 double strokes/min to 134 double strokes/min, and the wire-tension force can be reduced from 4 kg to 3.5 kg.

A reduction in the defectiveness of the turn insulation of the winding can be achieved by lowering the winding speed. For example, the defectiveness of the turn insulation of the winding (at a defectiveness of the wire insulation \(q_n = 0.08\)) can be reduced to 0.6, as against 0.755, which exists under the factory operating regimes of the winding machine. To do this, it is necessary to reduce the winding speed from 80 double strokes/min to 46 double strokes/min and to reduce the tension force from 4 kg to 3.5 kg.

The results obtained in this work make it possible to draw the following conclusions:

1. Deviation of the operating regimes of winding machines within the investigated range has a substantial effect on the quality of the turn insulation of windings of asynchronous motors.

2. A mathematical model has been obtained for defect formation in the turn insulation of asynchronous motors during winding manufacture; it takes into account the quality of the insulation of the incoming wire and the operating regimes of the winding machine.

3. The developed model makes it possible to find optimal operating regimes of technological equipment in order to increase its productivity and to improve the quality of turn insulation.

REFERENCES

1. L. M. Bernstein. Insulation of Electrical Machines for General Industrial Use. Moscow, “Energiya,” 1971.

2. E. K. Strelbitskii, O. P. Muravlev, Yu. P. Pokholkov. The influence of winding-and-insulating operations on the breakdown voltage of turn and frame insulation of asynchronous motors. Elektromekhanika, 1966, No. 1.

3. E. K. Strelbitskii, O. P. Muravlev, Yu. P. Pokholkov, A. S. Gitman. Investigation of the defectiveness of turn and frame insulation of random windings of asynchronous electric motors. Izvestiya TPI, vol. 180. Tomsk, TSU Publishing House, 1966.

4. Yu. P. Pokholkov. Reliability of the Insulation of Random Windings of Asynchronous Motors. Izvestiya TPI, vol. 242. Tomsk, TSU Publishing House, 1972.

5. V. V. Nalimov, N. A. Chernova. Statistical Methods for Planning Extreme Experiments. Moscow, “Nauka,” 1965.

6. Yu. P. Adler. Introduction to Experimental Design. Moscow, “Metallurgiya,” 1969.

7. L. Z. Rumshiskii. Mathematical Processing of Experimental Results. Moscow, “Nauka,” 1971.