Severe Overvoltage Research Articles

Evaluation of Switching Concerns Associated with 345 KV Shunt Capacitor Applications

This paper presents the most significant results of a comprehensive Transient Network Analyzer study evaluating approximately 2500 MVAr of 345 kV switched capacitor banks throughout central eastern and southeastern New York. The study evaluated various concerns associated with switched shunt capacitor applications. These concerns include transient overvoltages at the switched capacitor and other locations during normal and abnormal capacitor bank switchings. The paper evaluates surge arrester duties, switching device requirements, current limiting reactors, and design requirements to avoid possible severe overvoltages.

Advances in Capacitor Starting

An 8000-hp motor at the LOCAP Pipeline Clovelly Station is brought on line with three step capacitor starting and is protected from resonant overvoltage by a large metal oxide voltage limiter. Three-step starting is required to stay within the utility requirement of a maximum of ±1.5 percent primary voltage fluctuation during the entire starting operation. Cycle timers are utilized to obtain critical breaker sequencing as well as protect the system from breaker failure. Should the utility power fail while the motor is accelerating, the starting capacitor may cause severe motor overvoltage. Zinc oxide limiters are sized to absorb 1 MJ over a period of ten cycles allowing the breakers to clear the motor and capacitors.

Corona-Loss Characteristics of EHV Transmission Lines Based on Project EHV Research

Since 1960 the corona-loss characteristics of a variety of extra-high-voltage (EHV) transmission-line configurations have been under study at Project EHV [1], [2]. This paper presents results from the analysis of corona losses measured under all weather conditions experienced during 2½ years of observation of single or bundled conductors at 500 or 700 kV. In addition, corona characteristics are presented for switching-surge transients and severe steady-state overvoltages. The purpose of this paper is: 1) to summarize some of the statistical aspects of fair-and foul-weather corona-loss observations for the configurations studied, and 2) in terms of electrical and meteorological parameters, to describe an equation for corona loss on EHV lines that is in a form directly applicable by transmission engineers to EHV-line design.

Some regulated power supply apparatus using the Morgan circuit

The SCR chopper circuit has a very wide range of application in regulating a dc power, and its merits are universally appreciated. Because of its merits, the circuit is most suitable for a nonfailure power source that supplies power from a set of rectifier-batteries to a communication equipment or any other electronic equipment, which requires a dc power source of several output voltages. For such purposes, the output voltage of the circuit should be smooth, accurately regulated, and should respond quickly; at the same time, the efficiency must be high and reliability excellent. This paper offers, firstly, some improvements on the Morgan circuit in order to make it peculiarly suitable for different kinds of practical applications; namely, the smoothing filter is made as small as possible to make the response of the circuit rapid, while the efficiency is kept high. Secondly, data, obtained through the analysis of the operation in the case of the small filter, are presented. Thirdly, the paper shows, as the result of such analysis, that if a saturable current transformer (SCT) is designed properly, the circuit will behave as a self-regulating constant voltage power source. Lastly, it proposes a practical application which has a suitable protecting circuit composed of some simple circuit elements providing against the failure of commutation which causes a severe overvoltage and overcurrent to the load.

Extra-High-Voltage System Overvoltages Following Load Rejection or Hydraulic Generation

Dynamic overvoltages which might occur on a proposed 500-kv line of the Ontario Hydro were investigated to determine their effect on insulation, relaying, and other aspects of the system design. The most severe dynamic over-voltages occur if the receiving-end breaker opens leaving the line energized from the hydraulic generation.

Investigations of Switching Surges Caused by 345-Kv Disconnecting-Switch Operation

De-energization of 1,300 feet of 345-kv bus with a disconnecting switch produced severe system overvoltage. Although the overvoltages were effectively limited by lightning arresters to a value below the equipment insulation strength, a severe operating duty was imposed upon the lightning arresters. Unlike the high-voltage circuits, which are adequately protected, low-voltage power and control circuits can be damaged by induced overvoltages. This is particularly true of the 115-volt station-service and carrier-communication circuits. A series resistor connected in series with each pole of the disconnecting switch effectively eliminated overvoltages on the 345-kv system, and reduced the transients on the lower voltage circuits to a safe value. A porcelain-enclosed resistor has been developed to reduce overvoltage on the high-voltage system during bus de-energization. The resistor is automatically inserted into the circuit when the switch is operated, but is bypassed when the switch is closed.

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.

Switching surges with transformer load-ratio control contactors

THE INVESTIGATION described in this paper was undertaken to determine the magnitude and characteristics of the abnormal voltage transients accompanying the operation of load ratio control contactors on power transformers. As test results definitely established the fact that currents may be abruptly ruptured at other than normal current zero, accompanied by very severe over-voltages, the main purpose of the paper was directed to this phenomena, both from the experimental and theoretical viewpoint. It is believed that the subject will prove interesting to anyone concerned with switching surges in general, especially in view of the fact that certain aspects of the phenomena appear not to have been presented heretofore. Thus, the effect of current interruption at other than normal frequency current zero is gone into in detail; general equations on recurrent restriking are given; the extremely interesting possibility of restriking so as to practically discontinue the voltage transient is described; and the paradox of an increase in recovery voltage when shunt capacitance is increased is explained. These points are illustrated and supported by oscillographic evidence.