Overhead Ground Wire Research Articles

Insulated Overhead Ground Wires - Protective Carrier Relaying Investigations

The results of an extensive field investigation of the use of a single insulated overhead ground wire for protective carrier relaying are summarized and discussed. Transfer-trip relaying channels using either a single, continuous insulated ground wire or short insulated sections at each end of the line as carrier couplers are shown to be practicable. Balanced-pair operation of two insulated ground wires was not studied in field, however, the reliability for transferred-trip line protection is inferred to be poor.

Surges on Transmission Systems Due to Lightning Stroke on Overhead Ground Wire

Surges on Transmission Systems Due to Lightning Stroke on Overhead Ground Wire

Field Mapping Techniques for Lightning Protection

The lightning mast and overhead ground wire are well-established methods for protecting structures from direct lightning strokes. The advent of space vehicles and missiles with stored or contained propellants, and the exposure of extremely sensitive circuitry, compel the design engineer to investigate the degree of lightning hazard and to inquire into the margin of safety provided by these conventional methods of protection. Field mapping techniques and field equation analysis are powerful tools for such investigations. This paper presents a condensed discussion of basic lightning phenomena, field mapping methods for determining the pre-strike field conditions, and a field equation analysis of the transition from the static to the dynamic state. This analysis is provided for the pre-strike period, the lightning stroke and follow-through period, and is continued until static field conditions are restored.

Lightning Protection of Rotating Machines Directly Connected to Overhead Lines

Recommendations for lightning protection of rotating machines are presented. To protect the machine turn insulation, which is of primary interest, capacitors are placed at the machine and arresters out on the line. Minimum separation distances between the machine and most remote arresters are given for each machine voltage class. Variables are effectively or noneffectively grounded systems, ground resistance, expulsion or valve arresters, and use of overhead ground wire.

Lightning performance of 138-kv double circuit lines

THE COMMONWEALTH Edison Company operates a 138-kv and a 230-kv overhead transmission system in northern Illinois. Prior to 1954, most of the 138-kv circuits were carried on double circuit steel towers designed for two overhead ground wires. A typical 138-kv tower is shown as type A in Fig. 1. This tower has given very good lightning performance based on cumulative 6,351 year-miles of experience with circuits on towers where both circuits and both ground wires were installed, and 3,782 cumulative year-miles where only one circuit and one ground wire were installed. However, the type A tower had not given satisfactory service with respect to flashovers caused by galloping conductors under ice and wind conditions; for this reason, the type C tower in Fig. 1 was developed.

Analytical Studies of Lightning Performance of 1- and 2-Ground-Wire 138-Kv Double-Circuit Lines of the Commonwealth Edison Company

An unusual number of flashovers due to lightning have occurred on the 138-kv lines of Commonwealth Edison Company on a relatively new type of 138-kv double-circuit tower designed for only one overhead ground wire. Calculations based on the most recent AIEE Committee Report1 for estimating lightning performance indicate that these towers should have tripout rates very much similar to the type of double-circuit towers that are designed for two overhead ground wires. This paper goes a step beyond the AIEE Committee Report in that it considers the voltage surge induced on the conductors at the instant of field collapse through cloud discharge. This is done on a comparative basis for the new and old towers, as well as for modifications of the new towers. In addition, all towers are compared on a direct-stroke basis, in line with the AIEE Committee Report. A curve is presented which indicates a region where a second ground wire can be added to the new towers so that the resulting induced surge voltage and direct-stroke voltage compare favorably with previous designs. Actual modifications made in tower designs are discussed. These consist of: 1. changing the tower head to provide for two ground wires in a horizontal plane, and 2. adding a second ground wire at the height of the top phase conductor through the center of the tower.

Bureau of Reclamation 230-Kv Transmission Lines in North Dakota [includes discussion

A double-circuit 230-kv transmission line from the Garrison Dam power plant to Bismarck, N. Dak., and a singlecircuit 230-kv transmission line from Bismarck to Jamestown, N. Dak., were recently constructed by the Bureau of Reclamation as a part of the proposed ultimate system to transmit power from the Federal power plants on the Missouri River to wholesale customers in the Missouri River Basin. The lines are designed for National Electrical Safety Code heavy-loading conditions with additional vertical strength in the crossarms to support the conductors with 1½-inch radial thickness of ice. The conductors used on both circuits of the Garrison-Bismarck line are 795,000-circular-mil (CM) steel-reinforced aluminum cable (ACSR), 26 Al/7 st. The conductors on the Bismarck-Jamestown line are 954,000-CM ACSR, 54 Al/7 st. Two 1/2-inch high-strength-grade 7-wire class-A galvanized steel-strand overhead ground wires are used for the full length of each line. The design features of these transmission lines are typical of Bureau of Reclamation lines constructed since 1946.

Protective practices in high-voltage transmission

THE BONNEVILLE POWER Administration has adopted 345 kv for transmitting large blocks of power in the Pacific Northwest. The high initial investment required to transmit power at the higher voltages dictates the necessity for closely engineered practices. Revisions in practices that have resulted in lower costs for the 230-kv grid will be adopted for the 345-kv circuits and include: (1) reduced insulation levels, (2) high-speed automatic switching, (3) reduced lightning arrester levels, (4) elimination of provision for continuous overhead ground wire, (5) use of large single-phase autotransformer banks, and (6) elimination of spare single-phase transformers.

Lightning investigations at 115/230-kv stations

IN 1947 THE Hydro-Electric Power Commission of Ontario instigated a survey at its Burlington and Leaside 115/230-kv transformer stations to determine the effectiveness of the lightning protection provided by overhead ground wires, used to protect the stations from direct lightning strokes, and by co-ordinating gaps, used in place of the more conventional lightning arresters to protect the power transformers from severe overvoltages.

Experience with aeolian vibration in overhead ground wires

Observations indicate that wire tension is the most important cause of fatigue failure in overhead shield wires. These observations, and some of the remedial measures taken by one utility, are the subject of this article.

The failure of overhead ground wires caused by aeolian vibration

Vibration fatigue is a hazard to overhead transmission lines. A comparison is made in this article of several types of overhead ground wire construction and the methods used to avoid damage caused by vibration fatigue.

Protection of Transmission Line Over Mountainous Region Where Lightning Incidence Is High

This paper presents the application and beneficial results of protecting existing transmission lines which traverse mountainous country against direct lightning strokes by redesign of towers, alteration of overhead ground wires, installation of high speed relaying, and lowering of tower footing resistance by buried counterpoise wires.

Lightning Arrester Discharge Currents

DURING the last five years an investigation has been made of the discharge currents of a number of 38,000-volt lightning arresters. The transmission system on which these arresters were installed is operated with its neutral point earthed through Peterson coils; the lines are not equipped with overhead ground wires. The earth lead of each single-phase arrester was equipped with a pair of magnetic links. In addition, paper-puncturing recorders were used to indicate when arresters had operated.

Impulse and 60-cycle characteristics of driven grounds — III effect of lead in ground installation

GROUND installations comprise physically the ground proper and, in addition, a lead which connects the grounded part (protective device, insulator, overhead ground wire, lightning rod, and so forth) to the ground. The lead (grounding wire or metal structure) is essentially an inductance, while the ground acts as a resistance in the manner discussed previously. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> These two elements determine in a large measure the total voltage across the ground installation and therefore its performance under lightning discharges.

Practical Design of Counterpoise for Transmission-Line Lightning Protection

EXPERIENCE has shown that preventive lightning protection, involving the installation of overhead ground wires and the co-ordination of tower-ground resistances with insulation level, can be quite effective in preventing flashovers due to lightning. Studies presented in an earlier paper1 indicated that the efficiency of preventive protection can be made practically 100 per cent for high-voltage lines having insulator flashover levels of 1,600 kv and above. If the flashover level is reduced, the efficiency of protection becomes less.

Practical design of counterpoise for transmission-line lightning protection

EXPERIENCE has shown that preventive lightning protection, involving the installation of overhead ground wires and the co-ordination of tower-ground resistances with insulation level, can be quite effective in preventing flashovers due to lightning. Studies presented in an earlier paper <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> indicated that the efficiency of preventive protection can be made practically 100 per cent for high-voltage lines having insulator flashover levels of 1,600 kv and above. If the flashover level is reduced, the efficiency of protection becomes less.

Shielding of Substations

AS compared to transmission lines, it is more important that overhead ground wires or vertical masts over substations be correctly located so as to provide shielding of the structure against direct strokes of lightning. In a previously published paper1 the authors discussed the shielding characteristics required for transmission lines. The present paper extends these investigations to the shielding of substations.

Shielding of substations

AS compared to transmission lines, it is more important that overhead ground wires or vertical masts over substations be correctly located so as to provide shielding of the structure against direct strokes of lightning. In a previously published paper <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> the authors discussed the shielding characteristics required for transmission lines. The present paper extends these investigations to the shielding of substations.

Development in lightning protection of stations

THE AIEE transformer sub-committee has recently sponsored a paper <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> on the protection of power transformers against lightning surges. The most effective method given combines overhead ground wires, line entrance gaps, and transformer mounted lightning arresters. Such a method does give a high degree of protection, but it is primarily applicable to high voltage, high capacity stations where the overhead ground wire system is justified for both line and station. The conditions noted above are seldom fulfilled on subtransmission systems from 23 kv to 34.5 kv. Effective ground wires and low ground resistances are uneconomical, and the protection provided is usually a more or less modern arrester, not always located and grounded to the best advantage. On the 23-kv subtransmission system of the Duquesne Light Company, the average transmission distance is approximately two miles. This means that most direct strokes will contact the line not more than one mile from some substation. Much of this transmission is now equipped with wood cross arm braces and guy insulators, and at some stations several spans adjacent thereto are carried on unguyed poles.

Development in Lightning Protection of Stations

THE AIEE transformer sub-committee has recently sponsored a paper1 on the protection of power transformers against lightning surges. The most effective method given combines overhead ground wires, line entrance gaps, and transformer mounted lightning arresters. Such a method does give a high degree of protection, but it is primarily applicable to high voltage, high capacity stations where the overhead ground wire system is justified for both line and station. The conditions noted above are seldom fulfilled on subtransmission systems from 23 kv to 34.5 kv. Effective ground wires and low ground resistances are uneconomical, and the protection provided is usually a more or less modern arrester, not always located and grounded to the best advantage. On the 23-kv subtransmission system of the Duquesne Light Company, the average transmission distance is approximately two miles. This means that most direct strokes will contact the line not more than one mile from some substation. Much of this transmission is now equipped with wood cross arm braces and guy insulators, and at some stations several spans adjacent thereto are carried on unguyed poles.