TECHNO-ECONOMIC ASSESSMENT OF A COLLECTORLESS ELECTRIC-MACHINE AMPLIFIER OF INCREASED FREQUENCY

(BEMU-PCh-25A)

A. S. Baturin, A. I. Skorospeshkin, M. L. Kostyrev

(Recommended by the seminar of the Department of Electrical Machines and General Electrical Engineering)

The creation of a collectorless design of an electric-machine amplifier (BEMU) eliminates the shortcomings associated with the presence of sliding contact, increases reliability, and makes it possible to operate under more difficult service conditions.

In a number of cases, an automated drive requires an increased speed (more than 3000 rpm) from the special asynchronous motor of the actuating mechanism. One way of solving this problem is to create an electric-machine amplifier with an alternating-current output of increased frequency (more than 50 Hz). An acceptable solution to this problem has been obtained at the Department of Electrical Machines of the Tomsk Polytechnic Institute.

As a result of the studies carried out, an electric-machine amplifier with increased frequency (200 hertz) and an output power of 2.5 kW (BEMU-PCh-25A) was developed. This article gives an assessment of the new amplifier design.

For a techno-economic analysis of the new design, it is necessary to compare it with an EMU that can perform the same functions in automation circuits with identical output parameters. Such a comparison would be the most correct. However, ordinary EMUs do not have output parameters on alternating current, especially at increased frequency. In addition, at present domestic industry does not produce amplifier-converters that perform the same functions. Nevertheless, a comparison of the techno-economic indicators of the new design with an EMU makes it possible to evaluate its progressiveness. Based on these considerations, comparisons are given of the new design, with output on alternating and direct current, with the EMU-25A transverse-field electric-machine amplifier, which has the same power. Direct current at the output of the BEMU-PCh-25A is obtained according to Larionov’s circuit using VK2-10 semiconductor valves [7, 8]. Since the new amplifier can function only in nonreversible automation circuits, all comparisons are made for this operating mode. The techno-economic indicators for the variants under consideration are given in Table 1.

Analyzing the technical data (Table 1), we establish that the electrical indicators (voltage and power), as well as the energy and operating indicators (\(\cos \varphi\) and efficiency), are identical for the amplifiers being compared.

In terms of design indicators, however, the BEMU-PCh-25A in both versions has a lower weight (140 and 141 kg < 230 kg) and smaller overall dimensions.

Table 1

Techno-economic indicators for the amplifiers being compared
for non-reversing control circuits

B. Economic indicators

I. In manufacture

II. In operation

\((0.11\ \text{m}^3 < 0.175\ \text{m}^3)\) and is a more progressive amplifier according to these indicators.

It is also important that the new amplifier surpasses the EMU-25A in quality, which for these products is characterized by response speed and amplification factor. The amplifier designs being compared have identical amplification factors (2500), but in terms of response speed the BEMU-PCh-25A is the better amplifier \((0.12\ \text{s} < 0.20\ \text{s})\). As a result, the merit (quality) factor of the new amplifier in both versions considerably exceeds the same indicator for the EMU-25A \((21000 > 12500)\).

Thus, with smaller overall dimensions and weight, the BEMU-PCh-25A has higher quality in non-reversing automatic-control circuits in comparison with the EMU-25A amplifier currently being manufactured.

At the same time, when assessing technical progressiveness it is necessary to take into account a number of new valuable indicators of the new amplifier (BEMU-PCh-25A)—the collectorless design and operation at an increased frequency (200 Hz).

The absence of a commutator-brush assembly proves to be a decisive factor when choosing an amplifier for operation in an aggressive environment, at elevated humidity, in an explosive environment, in a dusty atmosphere, etc.

BEMU-PCh-25A may find application for high-speed controlled electric drives of precision metal-cutting machine tools (coordinate boring, grinding, internal grinding), for woodworking machines, and also in the chemical industry (centrifuges).

At present, high-speed drive is implemented according to the following scheme: an asynchronous frequency converter and a multi-speed asynchronous electric motor. In this case the speed is regulated in steps.

The use of the new amplifier will make it possible to carry out stepless speed regulation according to the EMU-PCh—motor with increased slip (AOS) scheme. The speed-control scheme thereby becomes more advanced. In addition, BEMU-PCh-25A can also be used as a higher-frequency generator for autonomous systems. The latter broadens the possibilities for applying the new amplifier.

Economic indicators are of great importance in analyzing new designs (Table 1, Section B). The wholesale price of BEMU-PCh-25A with an alternating-current output is higher than that of EMU-25A because of the additional costs of current rectification (Larionov circuit). If BEMU-PCh-25A is built with an alternating-current output at a frequency of 200 Hz, the new amplifier will have a lower wholesale price in comparison with EMU-25A (approximately 25 rubles less).

One of the substantial advantages of the new design is the reduction in copper consumption per amplifier (by approximately 2.8 kg per amplifier). Copper savings are achieved because BEMU-PCh-25A has no commutator-and-brush assembly.

The elimination of the commutator-and-brush assembly in the new design gives it one more important advantage over EMU-25A—better manufacturability. The introduction of BEMU-PCh-25A will be accelerated by the use in its design of previously mastered parts and assemblies employed in series-produced asynchronous motors. This will make it possible to put the new design into production quickly. Moreover, it can be mastered without incurring major expenditures.

Significant advantages of the new amplifier will appear in operation. Simplifying the design by eliminating the commutator-and-brush assembly reduces the repair-complexity category of BEMU-PCh-25A, compared with EMU-25A, by 0.8 conventional repair units [3]. On this basis, repair costs and the labor input for repair work are reduced by 19.5 percent, while labor productivity in repairs, compared with EMU-25A, increases by 24 percent. The somewhat higher cost of electrical-energy losses in BEMU-PCh-25A is explained by the higher no-load losses of the amplifier. In this calculation, the cost of losses was determined for operation during 4000 hours per year (two-shift operation, taking into account better utilization of the equipment). In addition, it was assumed that for 2000 hours the amplifier operates under load and for 2000 hours—in no-load mode. The power utilization factor was taken as 0.7.

In conclusion of the analysis of the economic efficiency of the new design, it is necessary to give a quantitative measure of the evaluation in monetary terms. For this purpose the economic indicators (Table 1) are converted into cost (monetary) indicators, which are presented in Table 2.

It follows from Table 2 that the capital expenditures \((K)\) for the amplifiers being compared are in approximately the same ratios as the prices, since they have increased by the amount of the costs of transportation to the consumer and installation costs.

The annual operating costs \((C)\) for BEMU-PCh-25A in both versions are lower than for EMU-25A.

Table 2.

Principal cost indicators of the economic efficiency of the compared amplifiers for non-reversing circuits

Final conclusions on economic efficiency must be made taking into account both capital \((K)\) and operating \((C)\) costs. This is reflected in the annual reduced costs [4]:

\[ C_i + E_{\mathrm{n}}\cdot K_i, \tag{1} \]

where \(i\) is the number of the variant under consideration;
\(E_{\mathrm{n}}\) is the coefficient of comparative economic efficiency, \(1/\text{year}\). For our case \(E_{\mathrm{n}} = 0.15\) [4]. A comparison of the annual reduced costs to the consumer (Table 2) makes it possible to draw final conclusions about the economic efficiency of the amplifiers. In non-reversing control circuits the BEMU-PCh-25A is a more economical amplifier in comparison with the EMU-25A.

Conclusions

1. The collectorless high-frequency electric-machine amplifier BEMU-PCh-25A, in non-reversing automatic-control circuits, is more economical than the EMU-25A.

2. The new amplifier has better response speed \((0.12 < 0.20\ \text{s})\), and has lower weight and smaller overall dimensions.

3. The BEMU-PCh-25A may find application as a contactless high-frequency generator for automated high-speed drives, and also for supplying autonomous systems.

4. The new amplifier has a more technologically manufacturable design, since it lacks a commutator-brush assembly and consists mainly of parts and units already mastered in electric motors. Less copper is required for its manufacture.

5. A significant economic effect is expected to be obtained in the operation of the BEMU-PCh-25A. Repair costs will be reduced by about 19.5 percent. In addition, in operation the new amplifier will be characterized by all the advantages of a collectorless machine (increased reliability, the ability to operate under difficult conditions—dustiness, elevated humidity, stable output parameters).

References

1. V. I. Radin. Electric-Machine Amplifiers. Gosenergoizdat, 1962.

2. Reference Data on Electrical Equipment. Vol. 1, Energiya Publishing House. Moscow–Leningrad, 1964.

1. Unified system of preventive maintenance and rational operation of technological equipment at machine-building enterprises. Mashgiz, 1964.

2. Standard methodology for determining the economic efficiency of capital investments. Moscow, 1966.

3. Supplement No. 1 to Price List No. 15-01. Wholesale prices for electrical machines of medium and low power. Moscow, 1965.

4. Price List No. 15-01. Wholesale prices for electrical machines of medium and low power, 1963.

5. Product nomenclature of the “Elektrovypryamitel” plant for 1966. Saransk, 1966.

6. Price List No. 16-03. Wholesale prices for semiconductor devices. Part 2. Moscow, 1966.

7. Winding data of asynchronous motors. Energia Publishing House, Moscow–Leningrad, 1966.

8. V. V. Rudakov. Electromechanical amplifiers in automation systems. GEI, 1961.