C. M. Laffoon

A New High-Voltage Insulation for Turbine-Generator Stator Windings

This paper reports the development of a new synthetic resin bonded mica tape insulation for high-voltage stator windings. It reviews the problems associated with earlier forms of high-voltage machine insulation. The general construction and processing of the insulation are described briefly. Comprehensive test data are presented on the characteristics of the materials employed and the resultant physical and electrical properties obtained on the composite insulation. This new insulation is now being applied to turbine generators for central station service.

Additional Losses of Synchronous Machines

In the case of high-speed turbine generators, the cost reliable means of determining the losses under actual operating conditions is to measure the weight and temperature rise of the cooling medium and to estimate the small part of the losses which is dissipated from the frame to the surrounding medium. The temperature rise of the cooling medium can be obtained by means of temperature detectors located at the inlet and outlet sections of the generator. In order to obtain reliable values of the average temperature rise for the machine, it is necessary to have approximately uniform velocities at both inlet and outlet sections and to measure the temperature rise at a large number of incremental sections. The volume of cooling medium passing through the machine can be determined by (a) introducing a definite amount of heat energy into the cooling medium and measuring its temperature rise, or (b) measuring the mean velocity head at the outlet section of a properly designed stock. Loss tests were made on five 3600-rev. per. min. turbine generators when operated as synchronous condensers. In the case of these machines, the additional losses including the increase in core loss at full kv-a. and zero per cent power-factor load varied from 3 to 22 per cent of the total losses. This corresponds to approximately 0.14 to 1.0 per cent of the generator input. The additional losses as measured under sustained short-circuit conditions were from 5 to 10 per cent less than the corresponding values for full kv-a.

Special Problems of Two-Pole Turbine Generators

Double-frequency rotor vibration due to different rigidity constants for the two major axes in two-pole 60-cycle generators can be eliminated by equalizing the rigidity constants on the two axes. This can be accomplished without introducing any reduction in flux capacity by machining narrow transverse slots in the body of the poles. The double-frequency vibratory forces inherent in two-pole generator stators cannot be eliminated. It is further believed that acceptable results cannot be economically obtained by reducing the air-gap magnetic densities and increasing the rigidity of the stator core over that normally obtained when magnetic conditions are adequately satisfied. Also the stator vibration is not of an amplitude considered to be harmful; consequently, the most practical solution is to isolate the stator core by means of flexible supports, and thus materially reduce the magnitude of the disturbing forces transmitted to the stator frame, foundation supports, and associated apparatus.

Short Circuits of Alternating-Current Generators

P. L. Alger: I have only one comment to make, and that is to remark that I believe the effect of saturation is quite an important one, especially in the application of the same type of theory to the initial currents of induction motors when they are thrown on the line in starting. Saturation makes the actual reactance of the machine much lower than it is when measured under normal conditions, and consequently, the initial current rush is much higher than might be expected, as in 25-cycle transformers, for example, where the ordinary flux is so high as to make the current rush saturate the iron very materially.

Hydrogen Cooling of Rotating Machines

Discussion of a paper by C. M. Laffoon published in the June 1936 issue, pages 703–9, and presented for oral discussion at the electrical machinery session of the summer convention, Pasadena, Calif., June 24, 1936.

Modern Practice in the Balancing of Large Turbine-Generator Rotors

In the manufacture of large high-speed turbine-generator rotors, balancing is instrumental in contributing to the over-all performance characteristics of the entire unit. Balancing equipment and instrumentation must be adequate to meet the rigorous demands imposed by shop production requirements. In addition, procedures and techniques must be capable of coping with the various problems that may arise in production balancing. This paper presents a review of the equipment and procedures introduced in shop and field balancing by the Westinghouse Electric Corporation as part of a continuing program of design and manufacturing development. It is hoped that the discussion may be of service in furthering an understanding of vibration control as reflected in the primary goal of improving machine performance.

Iron Losses in Turbine Generators

In large turbine generators there is no convenient method for determining the iron losses under load. It is the purpose of this paper to show, analytically, the factors influencing the change in iron loss with load. While very definite results are given for a simplified machine, it is not recommnended at this time that any change be made in the A. I. E. E. Standards for computing load loss, because there is miuch to be done before the work can be considered complete. This particular problem is typical of many which are entirely suitable for purely analytical study, and should furnish very desirable able work for investigators who do not have access to large machines for extensive tests, but who desire to carry on studies related to this type of apparatus. This, as well as similar loss problems, can be studied much more readily by theoretical work and model tests, than from measuring the total losses of an entire machine, because the value sought is never a predominant proportion of the total value measured; and even if satisfactory results be obtained on a particular machine, they are not generally applicable to all such apparatus. In this article, it is shown that on the basis of the flux distributions, the machines can be most conveniently divided into end zones, which present three dimensional problems and a large central zone, which presents only two dimensional problems.

Internally cooled generator coils increase ratings by one-half

A new method of cooling large turbine generators makes it possible to increase ratings by one-half. The technique consists of blowing hydrogen gas at high velocity through specially constructed hollow generator coils.

Variable-Speed Drive for United States Army Air Corps Wind Tunnel at Wright Field, Dayton, Ohio

THE machinery manufacturers are being required to solve many design and production problems in connection with our national-defense program. All electrical manufacturing companies are exerting maximum effort to produce generators, motors, conversion apparatus, and other electrical equipment which are needed in meeting the requirements of a large and rapidly expanding industrial activity. There is a further need for machines of greater capacity, new combinations of apparatus and control devices, and more information on machine characteristics to accomplish new and difficult objectives.

Increased Voltages for Synchronous Machines

The appreciable increase in the rating of generators, generating stations, and interconnected systems has resulted in large currents to be handled by generators, circuit breakers, reactors, cables, and station bus structures. This paper covers a discussion of the limitations on large generators and generating equipment by the present standard voltages of generation, the necessity for increasing the values of generated voltage, and the design, manufacturing, and operating problems involved in building high-voltage turbine generators.