A. J. McElroy

Rational Analysis of Electric Fields in Live Line Working

As voltage of electrical transmission systems increases, live line maintenance by the barehand method becomes increasingly necessary to meet the requirements of system reliability. Of more importance is its value to the workman in permitting him to use power and hand tools without the strain which would be encountered with the long, heavy, hot line tools required at these voltages. Protection of the workman from exposure to high-voltage gradients and body currents is easily attained through Faraday cage-type shielding, as has been proved by an extensive test program described in this and companion papers. This paper develops a method of predicting voltage gradients and body currents utilizing both analytical and numerical techniques in the solution of Laplaces equation. The results are compared with field measurements and excellent agreement is obtained. The method described can therefore be used to predict both currents and gradients for new designs and voltage levels as well as for existing designs and voltages.

Field Measurement of Switching Surges on Unterminated 345-Kv Transmisson Lines

Field measurements are presented for switching surge line-to-ground voltages at both bus and receiving ends of unterminated 345-kv transmission lines of intermediate length, when energizing and re-energizing. Varied and representative configurations were studied. Effects of source configuration and breaker-pole closing sequence and prestriking are demonstrated. An estimate of overvoltage probability is attempted as well as a rationalized description of waveforms. Comparison tests on 138-kv lines were conducted, and data presented therefrom.

On the significance of recent EHV transformer failures involving winding resonance

The recent failures of four EHV auto-transformer no load tap changers is interpreted. The failures were a direct and immediate consequence of transmission line faults as far as 340 miles away. The related system transient behavior is analyzed, and the transformer response to these transients is presented on a quantitative basis. It is demonstrated for these transformers that the ANSI standard dielectric surges offer an inadequate test of winding insulation remote from the line terminals where significant winding resonance is known to occur. The extent of these test limitations to other transformers is discussed.

Digital Computer Calculation of Transients in Electric Networks

This paper describes a new digital computer program for the solution of transients in linear electric networks. The program eliminates a number of obstacles uncovered through studying an earlier, published digital computer program. It is being applied to the solution of single-phase transient problems in power systems by several independent groups. The program may be applied directly to the solution of 3-phase problems, although further work in network reduction is required to this end.

Insulators with Contaminated Surfaces, Part I: Field Conditions and Their Laboratory Simulation

Physical and chemical analyses done on suspension insulator surface contaminants and fog water collected in the field showed significant water-soluble material in both. At one location the soluble material in both the fog water and surface deposit was gypsum, whereas the insoluble component of the surface deposit was mostly alpha quartz. A laboratory simulation system was used to produce flashover on a single-suspension insulator with contamination conditions and voltage typical of field experience. To achieve this it was required that the laboratory simulation of the fog include a horizontal wind and that of the surface deposit include a substance (bentonite was used here) that would allow water to permeate (spread out) on the surface. The simulation produced the major phenomena believed to occur when suspension insulators suffer contamination flashover.

Insulators with Contaminated Surfaces, Part II: Modeling of Discharge Mechanisms

This paper considers electrical discharge mechanisms as they occur across relatively dry zones on wet contaminated insulator surfaces. A mathematical model was assumed with constant surface resistivity, and constants were evaluated from experimental results obtained using a simple cylindrical geometry with a dry zone, wet contaminant, and electric stress much like those on suspension insulators.

Field Measurement of 345-Kv Lightning Arrester Switching Surge Perrormance

The purpose of this paper is to present lightning arrester switching surge voltages and currents, measured during a field test program on a 345-kv system. Surges were produced by energization of a transformer-terminated line and by ultra-high-speed re-energization (UHSR) of arrester-terminated lines. Arrester-sparkover levels were 1.1 to 1.7 pu (per unit) of arrester rating, and arrester follow-current peaks were 135 to 940 amperes.

Field Measurement or Switching Surges as Modified by Unloaded 345-Kv Transformers

This paper presents results and analyses of extensive field tests to determine how unloaded transformers affect switching surge waveform and magnitude when energizing and de-energizing intermediate-length lines. Particular emphasis is placed on transformer-terminated lines. Switching of transformer-tapped lines and low-side switching of combined autotransformer and connecting high-side line are discussed, and the results include data from tests on both 345-kv and 138-kv systems.

345-kV Switching Surge Tests Exploring Dynamic Voltage and Arrester Performance

This paper presents the results of switching surge tests on a 119-mile 345-kV circuit. For various methods of terminal switching, probability analysis is made of the magnitude and frequency of occurrence of transient and dynamic voltages when energizing the circuit through an autotransformer from systems with different soure impedances. Test results are compared with results of a model study on the same circuit. The good performance of current-limiting gap arresters is demonstrated in oscillographs showing arrester sparkover levels, discharge currents, reseal times, and reignition phenomena. The duration of dynamic voltages and the exposure of arresters to dynamic voltages above arrester rating are demonstrated. Data are presented on the transient performance and arcing period of 345-kV double-break disconnects when switching magnetizing currents of 200- and 400-MVA autotransformers.

Probabilistic Aspects of Transmission System Switching Surge Reliability

Probabilistic principles are applied to predicting the transmission system flashover rate caused by switching operations by combining results of laboratory tests on component insulation structures with system overvoltage probability distributions. A piecewise normal method is developed, applicable when statistical dependence of insulation structure flashover and system over- voltage generation cannot be described by standard normal distributions over the entire specified range of voltages. Results are obtained for large numbers of insulation structures in parallel and, by appropriately synthesizing the described sub-systems, entire transmission systems can be analyzed. The effect of voltage limiting devices, such as arresters, has been studied and their effect on system performance can be included in the analysis.