Toward Optimization of the Varnishing Process for Active Iron in Large Electrical Machines
Abstract Generated abstract
This article examines the optimization of varnishing electrical steel sheets for the active iron of large electrical machines, a process affecting both intersheet insulation quality and production efficiency. Using active experimental design, specifically a fractional factorial plan and Box Wilson steepest ascent, the authors studied the first varnishing operation for AS 4000 asynchronous motor stator sheets, varying conveyor speed and furnace zone temperatures while using intersheet insulation resistance as the optimization criterion. The experiments identified operating conditions that raised insulation resistance substantially compared with the plant’s existing process, and a second coating under similar conditions exceeded the required resistance level. The study suggests that planned experimentation can reduce the process from three varnish coatings to two while improving initial sheet quality, with further modeling proposed for resistance and varnish film thickness.
Full Text
On Optimizing the Varnishing Process of Active Iron in Large Electrical Machines
B. A. Itkin, S. M. Kabanova, A. A. Tarasyuk
(Presented by the scientific seminar of the departments of electrical machines and general electrical engineering)
Varnishing sheets of electrical steel is one of the principal characteristic technological processes in the production of large electrical machines. The study of a number of questions related to finding the optimal parameters of the varnishing process is of definite practical importance, since both the quality of the varnish film (the resistance of its insulation, thickness, etc.) and the productivity of the shop section (the speed of the varnishing-machine conveyor and the number of varnish applications) are connected with this. Although the technology currently used in electrical-machine building for varnishing active iron is far from new, we know of no generally accepted method for finding its optimal parameters. This situation is evidently explained by the fact that the varnishing processes themselves are rather complex, multistage, depend on many factors, and the methods used to study them have had an empirical-intuitive character. Usually, in a factory, work on adjusting the varnishing process was carried out by trying a number of values of its principal parameters and ended when data were obtained that were acceptable from the standpoint of production, without any possibility even of estimating how far they were from optimal. The use of methods of active experimental design greatly expands the possibilities for a purposeful search for optimal conditions [1].
This article presents the results of the first stage of a study, carried out jointly by the Sibelektrotyazhmash plant and the Department of General Electrical Engineering of NETI, on optimizing the varnishing process using experimental design by the Box–Wilson method.
The object of the study was the varnishing process for stator sheets of an asynchronous motor of type AS 4000. Under the technology adopted at the plant, the sheets of this machine usually underwent triple coating with varnish. It was decided first to determine the optimal parameters of the first varnishing process. The electrical resistance of the insulation between sheets was taken as the optimization parameter. Measurements were carried out on the factory installation on stacks of 20 sheets. The following factors were taken into account in the experiment: \(V\)—the speed of the varnishing-machine conveyor (m/min); \(T_1\), \(T_2\), \(T_3\)—respectively, the temperatures of the first, second, and third zones of the varnishing-machine furnace (°C). At the first stage of the work, a fractional factorial experiment was carried out with a half-replicate of type \(2_{\mathrm{IV}}^{4-1}\) [1]. Eight experiments were conducted, but it was not possible to regulate the temperature of the 1st zone according to the adopted design matrix because of the limited technical capabilities of the given furnace. The factor values of the 5th experiment, where the greatest value of the output ve-
…causes, the basic level of the subsequent half-replicate of the type \(2^{3-1}\) was adopted. \(T_1\) was stabilized within the range \(380 \div 390^\circ\mathrm{C}\). The planning matrix, the experimental results, and the steepest-ascent calculation are given in Table 1. These calculations were carried out according to the procedure and formulas in [1].
Table 1
| \(V\), m/min | \(T_2\), °C | \(T_3\), °C | \(R(y)\), ohm | ||
|---|---|---|---|---|---|
| Basic level | 20 | 585 | 500 | ||
| Range of variation | 2 | 15 | 20 | ||
| Upper level | 22 | 600 | 520 | ||
| Lower level | 18 | 570 | 480 | ||
| Coded values of variables | |||||
| Experiments | 1 | −1 | −1 | +1 | 31.1 |
| Experiments | 2 | +1 | +1 | +1 | 23.9 |
| Experiments | 3 | −1 | +1 | −1 | 20.8 |
| Experiments | 4 | +1 | −1 | −1 | 7.7 |
| Regression coefficients: | \(b_0=20.9\) | −5.22 | 1.65 | 6.6 | |
| Gradient components | −10.44 | 24.8 | 132 | ||
| Step for a change by 1 … | −1 | 2.35 | 12.66 | ||
| Rounding | −1 | 3 | 10 | ||
| Hypothetical experiments | 5 | 19 | 588 | 510 | 27.2 |
| Hypothetical experiments | 6 | 18 | 591 | 520 | 34.7 |
| Realized experiment | 7 | 18 | 590 | 510 | 38 |
| Secondary varnishing | 8 | 18 | 590 | 510 | 80 |
Steepest ascent proved to be very effective: the seventh experiment gave \(R=38\), which is 3.1 times greater than the insulation resistance of the sheets of the control batch on the same varnishing machine (\(R_k=12.3\)), obtained with the parameters of the commonly used technology. Secondary varnishing of sheets with parameters analogous to experiment 7 gave the value \(R_8>80\), which significantly exceeds the minimum permissible insulation resistance for these sheets.
Thus, application of the method of active experimental planning already at the first stages of studying the varnishing process for AS 4000 sheets made it possible to move from a threefold to a twofold varnish coating while simultaneously improving the initial quality of the sheets. In further studies it is intended to obtain a mathematical model and to optimize the varnishing process both with respect to \(R\) and with respect to the thickness of the varnish film, taking into account the factors of zone temperatures, speed, conveyor, varnish viscosity, and roller pressure.
REFERENCES
- Yu. P. Adler et al. Planning an Experiment in the Search for Optimal Conditions. “Nauka,” 1971.