Philip Sporn

Rationalization of Transmission System Insulation Strength

Experience on high-voltage transmission lines has shown numerous failures of apparatus which have indicated a decided lack of coordination of the insulation strengths of the various parts of the transmission system. Apparatus offered by manufacturers for a given service shows wide variations in insulation values. Again the flashover and the breakdown values are not at present sufficiently standardized to be comparable among manufacturers of the same piece of apparatus. The standard tests on different types of apparatus are not properly correlated. This paper, besides discussing the above situation, points out the causes for the present status, and indicates the benefits to be derived by grading the insulation on the entire system. Predetermining the point of electrical breakdown on the system in the case of high voltage surges leads most logically to grading the insulation. This grading should result in fewer major service interruptions, with a localization of trouble on a link of the system where repairs can be made easily and inexpensively. The paper points out that additional information is required on surge voltage breakdown of insulation to solve the problem completely but shows that with the present information available a start in grading can be made. The different links in the transmission chain are tabulated according to their relative importance and with this as a starting point, the entire grading scheme is developed to the point of showing relative 60 cycle insulation strength required of the different apparatus used on a transmission system.

Tests on High-and Low-Voltage Oil Circuit Breakers

Data from a large number of tests on several types of oil circuit breakers are given in this paper. The tests were made on breakers with the following ratings: (a) 150 kv., 1,500,000 kv-a.; (b) 35 kv., 250,000 kv-a.; (c) 7000 volts, 7500 kv-a.; (d) 132 kv., 1,250,000 kv-a., and (e) 132 kv., 750,000 kv-a. These tests were made on power systems having sufficient connected capacity to make the tests conclusive. Complete data are tabulated and oscillograms are shown. Some valuable conclusions resulted from the tests.

1927 Lightning Experience on the 132-Kv. Transmission Lines of the American Gas and Electric Company

A record of the 1929 lightning performance of a 1,200-mile 132-kv. transmission net workis given, and compared with the record of the system during the previous three years. The system is almost entirely of steel tower construction with conductors in vertical configuration; and on most lines one ground wire is employed. It is shown that some 75 per cent of high-voltage transmission line outages on this system are due to lightning. Lightning performance of lines being dependent on the severity of lightning conditions, a record of these conditions should be kept from year to year if records are to be compared. Data are presented on relative yearly lightning intensity, line outages, damage found to insulators and hardware, performance of double circuit lines, lines with and without ground wire, and with two ground wires, and also with and without grading shields. The apparent part tower footing ground resistance plays in line outages due to lightning is also given. The conclusions are drawn that 1. Two circuit lines are far more reliable, from a lightning point of view, than single circuit lines. 2. One ground wire offers considerable protection against lightning, and two ground wires considerably more. 3. Grading shields properly applied do not reduce line outages but decrease the damage to insulators, hardware, and conductors. 4. Both direct and induced lightning strokes have to be considered on these lines. 5. Flashovers do not always concentrate on high tower footing resistance towers. 6.

1926 Lightning Experience on 132-Kv. Transmission Lines

This paper deals with the interruptions due to lightning on an extensive interconnected 132-kv. system during the year 1926, a similar record covering part of the system having been reported previously.2 A layout of the system is shown and details of the type of line and tower construction are given in considerable detail. The lightning performance of different sections of the line have been reduced to a common basis and discussed from the point of view material of line structure, height of line, ground wire, and line protective equipment. Changes in tower design are discussed in the light of experience gained in the past. The work done the past year to reduce the lightning troubles at the stations is described. The efficacy of the ground wire seems very definitely shown but it is believed further study and attention should be given this matter as a means of reducing the lightning voltage on transmission lines, particularly to reducing the lightning voltage at and near a switching station. The problem of determining the damage to linie conductors, etc., is an important one. Data on this are at present incomplete, but it is planned to obtain a systematic record in the future which will, it is believed, supply valuable design information.

Lightning Investigation on the Ohio Power Company's 132-Kv. System

Description is given of the Lightning Field Investigation on the 132-kv, Philo-Canton, 73-mile, two-circuit line made during 1929 with surge recorders, cathode ray oscillograph, lightning stroke recorders, and a lightning generator. Data are presented on the magnitude of lightning voltage surges, the attenuation of these surges as they travel along the line, and the difference in attenuation between positive and negative lightning surges. The preponderance of positive lightning surges is indicated; but the fewer negative surges produce the highest voltage on the line. The lightning stroke recorders gave data on the polarity of the direct strokes, and the magnitude of the current in the lightning stroke. Lightning arrester performance on lightning and switching surges is analyzed, and typical surges obtained by the cathode ray oscillograph are given for both cases. The magnitude and shape of lightning waves occurring on the line are shown and these waves analyzed as to duration of front, tail, and total length. These data are discussed as they relate to the proximity and rate of discharge of clouds producing lightning surges. General conclusions are drawn based on the data obtained in the investigation.

Rationalization of Transmission Insulation Strength---II Need for, Present Status, and Necessary Developments for Carrying Through

This paper, prepared with the cooperation of the members of the Insulator and Lightning Subcommittee, points out the present need for rationalizing transmission system strength on the basis of lightning voltage. The higher grade of service demanded of transmission systems today requires fewer interruptions. It is pointed out that for a four year period the line interruptions due to lightning on an extensive 132-ky. network average 75 per cent of all line outages. Apparatus failures due to lightning, while not numerically great, can be materially reduced, if the system insulation is coordinated on the lightning basis. Over-insulation of lines has been tried in some cases, particularly on wood pole lines, with varying degrees of success in reducing line outages. But this method of attacking the lightning problem does not consider the protection of station equipment where the most costly apparatus is subject to damage, and where apparatus damage may result in long service outage. It is pointed out that additional knowledge is necessary on lightning strengths of insulation and apparatus to rationalize system voltage strengths on a lightning basis. This information is gradually being secured by various groups working on the problem. To aid in solving the lightning problem it is proposed a set of standard test waves be adopted by which insulation and apparatus, if possible, may be tested.

Abridgment of 1928 lightning experience on 132-kv. lines of the American gas & electric company

This paper gives the operating experience of some thousand miles of 132-kv. transmission lines analyzed from the lightning point of view. The lightning experience during three years operation of the system is compared. In addition, the effect of ground wires, grading shields, and tower footing ground resistances is discussed from data secured under operating conditions. The comparative reliability of single- and two-circuit lines is analyzed from the data recorded. Cases of damage to insulator strings, hardware, etc., are tabulated and discussed from the point of the severity of the damage and the location on the phase wires. Yearly averages of lightning outages per 100 mi. of line per year are given for the different lines and from these figures comparisons made for the different types of line construction. A three year record is given of the percentage of lightning outages on the 1000-mi. network.

Surge Voltage Investigation on the 132-Kv. Transmission Lines of the American Gas and Electric Company

Data on the surge voltage investigation, carried out under the auspices of the Subcommittee on Lightning, on one of the 132-kv. lines of the American Gas and Electric Company during 1928, are presented. Most of the surges have been segregated as to cause, and plotted in summary form for more convenient use. The magnitude and character of recorded surges are discussed; and the conclusions drawn from data presented. Information on voltage surges due to lightning, switching, trip-outs, and unknown causes are presented, as well as records of lightning arrester discharge currents, voltages across choke coils, and on the ground wire. This paper is presented at this time to make available to the engineering profession some of the information obtained, before the report of the Subcommittee on Lightning is completed. As experimental work is still being done in the field during 1928, anything like a complete report cannot be made until next year.

Abridgment of rationalization of transmission insulation strength — II: Need for, present status of, and necessary developments for carrying through

This paper, prepared with the cooperation of the members of the Insulator and Lightning Subcommittee, points out the present need for rationalizing transmission system strength on the basis of lightning voltage. The higher grade of service demanded of transmission systems today requires fewer interruptions. It is pointed out that for a four-year period the line interruptions due to lightning on an extensive 132-kv. network average 75 per cent of all line outages. Apparatus failures due to lightning, while not numerically great, can be materially reduced if the system insulation is coordinated on the lightning basis. Over-insulation of lines has been tried in some cases, particularly on wood pole lines, with varying degrees of success in reducing line outages. But this method of attacking the lightning problem does not consider the protection of station equipment where the most costly apparatus is subject to damage, and where apparatus damage may result in long service outage. It is pointed out that additional knowledge is necessary on lightning strengths of insulation, and apparatus to rationalize system voltage strengths on a lightning basis. This information is gradually being secured by various groups working on the problem. To aid in solving the lightning problem, it is proposed that a set of standard lest waves be adopted, by which insulation and apparatus if possible may be tested. With this knowledge of the lightning insulation strength of apparatus, it will be possible to design transmission systems more intelligently on a lightning basis so far as insulation is concerned, in addition to the present 60-cycle basis. On the basis of field data secured last year on wave-shapes of natural lightning, three standard test waves are proposed, having voltage — time characteristics similar to those actually observed. It is pointed out that lightning voltage should be designated in units peculiar to lightning and not in terms of 60-cycle voltage values.

Experience with Carrier-Current Communication On a High-Tension Interconnected Transmission System

The paper gives a historical outline of the development of carrier-current communication on power systems. It discusses the principles of the various systems of carrier current developed to date and outlines the fundamentals of a carrier communication system over a transmission network. A description of the installations on a 132-kv. network having an extent of 2500 linear miles is given and the general experience with carrier, which is the sole means of communication operated and provided by the power companies on that system, is outlined. A carrier-current communication system is analyzed into its component parts and the experience with these various parts given. Extensive experience with various forms of couplings, various forms and makes of coupling capacitors is described. Experience with the protective system, the lead-in system, and the tuning used in connection with the coupling is given in detail. Detailed experience is given with the transmitting system and the receiving system of various makes of carrier employed. An outline of the experience with the various makes of power supply is given. A discussion of the operation of carrier on a large system such as the one described and the necessity for zoning and interzoning is given and experience in establishing and maintaining these zones is outlined. Definite data are cited as to cost, maintenance, reliability, traffic, and safety. A description of various types of portable sets developed and their use is given.