Graham Lee Moses

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.

Alternating and Direct Voltage Endurance Studies on Mica Insulation for Electric Machinery

A program studying voltage endurance of various mica insulations is reported. This includes dielectric breakdown data with both alternating and direct current on numerous similar samples. Effects of repetitive testing, prolonged a-c (60-cycle) stress and mechanical damage to mica insulation are reported. Detection of insulation faults is described and conclusions are drawn that d-c overpotential maintenance tests can be equally searching but less damaging than a-c overpotential tests for large high-voltage rotating machinery.

Re-examination of temperature standards for electrical insulation

Information is presented which indicates that standards are still inadequate to differentiate clearly the temperature classes of insulation and several changes are suggested to improve and broaden those standards.

Winding-Fault Detection and Location by Surge-Comparison Testing

Surge-comparison methods of testing insulation were investigated with the objective of locating as well as detecting faults. Experience of other investigators was confirmed and limitations of methods and equipment studied. Supplementary methods and equipment were devised to extend the field of usefulness of this basic type of tester, especially to the testing of very large machines with multiple-parallel windings. Apparatus studied included a-c motors from fractional-horsepower single-phase to very large three-phase types; a large variety of d-c armatures; and numerous armature, stator, and magnet coils. This surge-comparison tester has proved to be suitable for use by electrical manufacturers and by service and repair shops, as it can be used for testing most common types of electric windings.

Investigation of Silicone Insulation on High-Temperature Railway Motor

Thermal aging and humidification tests are reported on a silicone insulated railway motor. This included 1,675 hours at a temperature of 285 degrees centigrade with 46 cycles of severe humidification. Loss of initial moisture resistance was observed but no operating failure occurred. No change occurred in the heat dissipating characteristics of the machine. Finally, the motor was dismantled and the insulation examined in detail. Thermal aging data are interpreted.

Effect of Altitude on Electric Breakdown and Flashover of Aircraft Insulation

ELECTRIC power to operate auxiliaries is now an indispensable requirement of modern aircraft. Within the past ten years the electric load on an airplane has increased more than tenfold.1 The optimum voltage for electric systems for large aircraft already has more than exceeded the present 24-volt standard,2,3 and the use of higher-voltage systems, already tried experimentally,4 now appears to be a certainty. Moreover, the operating altitudes of modern airplanes, particularly military craft, are climbing steadily to ever increasing heights. Each of these factors indicates a need for a careful study of the requirements for insulation of aircraft electric apparatus in order to achieve minimum weight and space without sacrifice of reliability. A preliminary study of this subject was made and reported5 prior to the use of the 120-volt a-c system on the XB-19, but the projected use of 208-volt systems4 for still higher altitudes makes a more comprehensive study of this problem most timely.

Surge Protection for Pipeline Motors

Recent field tests on motors in service on pipelines and powerhouse systems have shown that the switching surge voltage appearing at the motor terminals during initial energization for starting frequently reach magnitudes approaching 2.0 per unit normal crest line-to-ground operating voltage with time-to-crest as short as 0.2 As. This is more severe than normally believed and may endanger turn-to-turn insulation.

Organo-Silicon Compounds for Insulating Electric Machines

Discussion of paper 45–30 by T. A. Kauppi and G. L. Moses, presented at the AIEE winter technical meeting, New York, N. Y., January 22–26, 1945, and published in AIEE TRANSACTIONS, 1945, March section, pages 90–3.

Stator Insulation Practices for High-Voltage Inner-Cooled Generators [includes discussion]

Inner cooling of high-voltage generator stator coils1,2 has made possible greatly increased ratings for the active magnetic and conductor materials in large hydrogen-cooled machines. This major advance in cooling. technique has required modification in some insulation design practices and application methods. It is the purpose of this paper to review the insulation of large inner-cooled generators and to re-examine the basic insulation methods and concepts. Test data on models and insulating structures in hydrogen at various pressures are reported. The philosophy for design of creepage distances across insulating surfaces and striking distances through gas is discussed.

Silicone-Resin-Treated Magnet Coils

MAGNET COILS present somewhat different insulation problems from rotating machines. This was recognized when separate magnet coil standards1–3 were set up by AIEE, National Electrical Manufacturers Association, and American Standards Association which permit higher maximum observable temperatures than do the rotating machine standards. AIEE Standard 1 states, “How long an insulation will last will depend not only on the class of material used but also upon the physical support of the insulation and the severity of the physical forces tending to disrupt it.” Following this line of reasoning, AIEE Standards 15 and 16 permit higher observable temperatures on magnet coils as shown in Table I. Work by Erikson4 indicates the desirability of separate consideration of magnet coils and suggests the possibility of higher operating temperatures even with organic insulation.