Charles L. Wagner

Multistep Resistor Control of Switching Surges

For system voltages above 500 kV the conventional one-step resistor cannot limit switching surge overvoltages to the desired level of 1.7 per unit or less. This paper presents the results of an analog computer study of four possible methods of controlling switching surge overvoltages with a breaker and/or resistors. The alternatives studied include synchronous control of closing without a resistor, a ganged three-resistor breaker, a ganged two-resistor breaker, and a controlled closing two-resistor breaker. Overvoltage limits and breaker timing criteria are obtained for each alternative.

Insulation Coordination for Gas Insulated Substations

This paper presents the development of BIL (Basic Lightning Impulse Insulation Level) ratings for SF6 gas insulated substations from 72.5 kV to 765 kV. The unique properties of the gas insulated substation are analyzed and insulation coordination design techniques are utilized to determine BIL ratings for the substation equipment, other than the transformer, with a lightning arrester located at the entrance terminals. The resulting analysis shows that, in general, the required BIL level of apparatus for gas insulated systems can be lower than for conventional equipment because of lower surge impedance and shorter lengths of the gas insulated bus.

Analysis Of Transient Recovery Voltage (TRV) Rating Concepts

The basis for TRV standards both ANSI and IEC were developed about twenty years ago. While the requirements are similar, there are significant differences. These differences are examined with some of the assumptions behind them. With the recent emphasis towards harmonization of ANSI and IEC standards, it appears that the data and assumptions need to be re-examined. This paper is a start in this direction with the aim to provoke further study by the respective standards groups.

Insulation Levels for VEPCO 500-Kv Substation Equipment

A detailed study has been made of the Virginia Electric and Power Copmany (VEPCO) 500-kv transmission sytem to determine optimum insulation levels for the substation equipment. Results of this study depend on both economic and technical considerations. For the VEPCO system, a 70% arrester can be used at the generator step-up transformer locations, and a 75% will be required at step-down substations. Adequate impulse and switching surge margins permit a transformer BIL (basic impulse insulation level) of 1,300 kv to be used at all locations. The most practical circuit breaker BIL, consistent with good engineering practice and economy of application, is 1,550 kv.

Evaluation of Surge Suppression Resistors in High-Voltage Circuit Breakers

The switching surge insulation level of steel tower and wood pole transmission lines operating at system voltage levels of 115 through 500 kV are compared with the switching surge magnitudes that can occur on these systems. High-side and low-side switching with and without surge suppression resistors is considered. The results indicate that at 345 kV and above surge suppression resistors should be used, while below 345 kV these resistors cannot, in general, be justified.

Transient Overvoltages Caused by the Initiation and Clearance of Faults on a 1100-kV System

Overvoltages on UHV systems may be controlled to a level of 1.5 pu or less. Historically, lightning, line energizing, and line reenergizing overvoltages have been the primary factors in establishing power system design levels. At the new reduced levels, other transients must be considered. Fault initiation and fault clearing transients are investigated using different system configurations. Minimum levels are established by fault initiation transients. Fault clearing overvoltages can be controlled to corresponding levels by the insertion of opening resistors.

Performance of Excitation Systems Under Abnormal Conditions

Modem generator excitation systems provide good voltage regulation at normal system frequency and assist in maintaining transient stability during disturbances. However, a number of abnormal system operating conditions should be considered in evaluating excitation system performance. Some of these conditions are extended periods of operation at other than normal frequency, or voltage, or both, simultaneously. These system conditions can cause excessive output from the generator excitation system and impose overloads on the generator and step-up transformer.

New Generation Of Oilless Circuit Breakers 115 KV-345 Kv I. System Requirements

Circuit breakers in this decade will have to satisfy demands, not only for increased ratings but also for reliability, ability to function under multiple contingency situations, reduced environmental pollution, versatility of application, and reduced installation and maintenance costs. The system requirements which new circuit breakers need to meet in order to satisfy these new demands are given. A new line of circuit breakers that satisfies these demands is described. The paper introduces a set of accompanying papers that describe the interrupting, insulating and mechanical systems of this new breaker line in detail.

Open Breaker Protection of EHV Systems

Although the use of line-entrance lightning arresters provides absolute protection for an open breaker condition, it represents a costly installation. No line entrance protection represents some risk of breaker damage. Line entrance rod gaps offer a compromise between these extremes. This paper discusses the probabilities of failures using these three alternatives and describes a procedure whereby the spacing of the line-entrance gap can be determined. Since this procedure depends on the particular configuration of the gap being used, test data are presented on one particular configuration used on a 345-kV system. Based on these data, recommended gap spacings for 345-and 500-kV systems are developed.

Verification Tests of the VEPCO 500-kY System

The results of the first field tests performed to verify the design of the Virginia Electric Power Company 500-kV system are presented. Initial radio influence measurements made on each line section are compared with levels calculated during the design studies. Switching-surge voltages recorded during various normal and abnormal switching conditions are given, and are shown to be well within predicted values. Descriptions are given of the measuring equipment and techniques used for the field tests and for a continual monitoring of the system.