W. W. Lewis

Protection of Rotating A-C Machines Against Traveling Wave Voltages Due to Lightning

The problem of providing protection for rotating a-c machines against lightning overvoltages has two parts: 1. The protection of insulation to ground, which is mainly a question of the magnitude of the overvoltage, and 2. The protection of turn insulation, which is primarily a matter of wave front. To meet the first requirement, the overvoltage to ground must be limited to a safe value. This is assumed to be approximately equal to the crest value of the 60-cycle high potential test. To fulfill the second requirement, the turn voltage gradient must be limited to conform to the turn insulation. To secure these results, a protective scheme is proposed, which includes arresters 2,000 feet and 500 feet out on the line, or other means, to limit the incoming voltage to 2.5 times the crest value of the terminal arrester rating, a special arrester at the machine terminal to limit the voltage to the crest value of the machine high potential test, and a capacitor at the machine terminal to slope the wave front, thus limiting the turn-to-turn stresses. The capacitor also serves to limit internal overvoltages due to reflection at the neutral. For neutral grounded solidly or through resistance equal to or less than the combined surge impedance of the machine windings 0.1, μf capacitance is sufficient; while for isolated neutral, capacitance up to 0.5 μf may be necessary. Ground wires over the line for the initial 2,000 feet are recommended to protect against direct strokes.

Symposium on Surge Voltage Investigations Surge Voltage Investigation on Transmission Lines

This paper and companion papers discuss the surge voltage investigation on six power systems in the lightning season of 1927. Valuable data have been secured as to the nature and polarity, magnitude, wave-front and attenuation of surges, also the effect of overhead ground wires, choke coils, and lightning arresters. Especially interesting is the attenuation formula A = k e2, the form of which indicates a close connection between attenuation and corona loss. Further investigations are being carried on in the present year to secure more complete and exact data on wave shape and attenuation, effect of ground wires, lightning arresters, and choke coils.

Lightning Investigation at High Altitudes in Colorado

THE operation of transmission and distribution lines in the high altitudes of the Rocky Mountain region had indicated that lightning strokes were not so severe as at lower altitudes. Also glow discharges or corona currents from the earth have been observed at high altitudes from pointed objects and rocks. This investigation was made to determine the probable lightning current at altitudes from 6,000 feet to 13,500 feet and to measure corona current. It has been found that the probable stroke current decreases with increase of altitude from sea level to approximately 18,000 feet altitude at which point it appears that no current would be present. The highest mean temperatures at 18,000 feet do not exceed 32 degrees Fahrenheit, and comparison of temperatures in free air at altitudes up to 13,500 feet check temperatures on the earths surface and indicate that freezing temperatures may limit the formation of lightning.

The Neutral Grounding Reactor

A neutral grounding reactor (Petersen Coil) has been in operation on the system of the Alabama Power Company since October 12, 1921. This is the first of these devices in this country, although there are perhaps several hundred of them in operation in Europe. The present paper discusses the tests made shortly after installation of this reactor. A companion paper by Messrs. J. M. Oliver and W. W. Eberhardt, discusses the operation of the reactor for a period of about a year. It is believed that this device has a somewhat limited use in this country on account of the prevalence and popularity of the solidly grounded neutral. Nevertheless, there are certain installations favorable to the use of the reactor and it is partly the purpose of the present paper to outline the field of this device as well as to show how its rating may be determined for a particular system.

Study of Driven Rods and Counterpoise Wires in High-Resistance Soil on Consumers Power Company 140-KV System

THE Consumers Power Company operates an extensive 140-kv system in eastern, southern, and western Michigan. In parts the top soil is sand, sometimes extending to a considerable depth, and tower footings in this soil have very high resistance compared with resistance encountered in other soils.

Co-ordination of insulation and spacing of transmission line conductors

A SURVEY of practice on existing transmission systems shows, for the same operating voltage, wide variations in the insulation used. Also, wide variations occur in the spacing between conductors and from them to grounded members of the supporting structure.

Abridgment of lightning investigation on transmission lines

The surge voltage investigations, 1926 and 1927, are briefly reviewed, and data given for 1928 and 1929. The cathode ray oscillograph has played a prominent part in the last two years work, and about 115 oscillograms have been obtained. The following new instruments were introduced in 1929: Lightning stroke recorders; field intensity recorder; and rate of change of field intensity recorder. A vast amount of progress has been made in the solution of the lightning problem. Personnel, equipment, and technique are available for the complete solution of the problem by means of field and laboratory studies, carried on simultaneously and supplementing each other.

Abridgment of surge voltage investigation on transmission lines

This paper and companion papers discuss the surge voltage investigation on six power systems in the lightning season of 1927. Valuable data have been secured as to the nature and polarity, magnitude, wave-front and attenuation of surges; also the effect of overhead ground wires, choke coils, and lightning arresters. Of special interest is the attenuation formula A = k e2, the form of which indicates a close connection between attenuation and corona loss. Further investigations are being carried on in the present year to secure more complete and exact data on wave shape and attenuation, effect of ground wires, lightning arresters, and choke coils.

Abridgment of relation between transmission line insulation and transformer insulation

Principles to be followed in transmission-line construction in order to reduce damage from lightning are recommended in this paper. The major recommendations are as follows: (1) Keep transmission conductors low and arrange horizontally, (2) use ground wires, (3) use sufficient insulation but of a sufficiently low value near stations to protect apparatus, (4) install lightning arresters at the transformers. The arguments leading to these recommendations are outlined in the paper.