Switching Surge Voltage Research Articles

A combined engineering model for the analysis of switching surge flashover characteristics of long air gaps

The flashover characteristics of long air gaps submitted to switching surge voltages may be predetermined by use of a mathematical model of leader propagation. The present model is developed from each combination of previous engineering models, and is also applied to positive rod-to-plane geometries with gap lengths up to 20 m. However, four parameters to determine leader propagation with respect to our model are adjusted in the present calculation so as to fit experimental flashover voltages and calculated flashover voltages which depend on waveforms of the applied voltage and gap length. The calculations show that these parameters are only a function of gap length. Our combined engineering model using parameters that depend on gap length allows the flashover characteristics of long air gaps to be easily determined with a microcomputer.

Puncture breakdown characteristics of protected rubber insulating gloves

The results of puncture breakdown tests on rubber gloves are presented. A positive polarity switching surge voltage (275/2500 mu s) or a 60 H alternating voltage was applied to the glove to cause breakdown. The effect of mechanical pressure on glove breakdown behavior and the influence of using a leather protector were investigated. It was found that protected gloves are more likely to break down at a position other than where the needle electrode has been placed. In both AC and switching surge breakdown tests, the standard deviation in breakdown voltage for protected samples was greater than that of the nonprotected samples by 25%. Under AC conditions, with mechanical stress applied, a bare glove will break down at a voltage which is approximately 22% below the nonstressed condition. A protected glove which is mechanically stressed will break down at a value 12.75% below the nonstressed condition. It is suggested that the results obtained will help to determine the operating limits and reliability of the glove insulation. >

Volt-Time Characteristics in Air, SF6/AIR Mixture and w2 for Coaxial Cylinder and Rod-sphere Gaps

This paper reports volt-time characteristics of air and air mixture with 1% SF6 additive for a 1.25 5.2 cm coaxial-cylinder gap. The surge voltages used included waveshapes of 0. 260 Ps, 1.25660 ps impulse voltages as well as 1511200 ps, 275/2500 , us switching surge voltages. The experimental pressure ranged from 100 to 500 kPa (absolute) Additional tests were conducted using rod-shpere gaps in dry air and nitrogen. For steep-fronted impulses the breakdown values decreased with increasing the rate of rise of voltage. The effect depended upon the polarity of the voltage, the pressure, and the nature of the gas.

Surge and Noise Generation in a Forward DC-to-DC Converter

Switching surge and noise voltages are analyzed under the common-mode condition in a forward dc-to-dc converter. The analysis is performed by partitioning the switching time into several states and introducing the high-frequency equivalent circuits. The equivalent circuits include not only inductive and capacitive parameters, but also the parameters related to the switching speed of the transistor and the recovery characteristics of the diode. As a result, the effects of these various parameters on the surge and noise generation are made clear quantitatively.

Switching Surge Voltage Distribution in Superconducting Generators

This paper is focused on describing how to calculate voltage surges caused by vacuum circuit breaker interruption in an air-core armature winding. The method developed is based on a simplified lumped parameter model of the winding and a simplified model of vacuum circuit breaker behavior. It is necessary to estimate the surge voltage distribution and turn-to-turn insulation requirement to obtain a rational design before such a winding can be designed and built. In this study the Fast Fourier Transform method is used to compute the surge voltage waveform. The 10 MVA superconducting generator built at MIT for the Department of Energy is used as an example.

Switching Surge Voltage Distribution in Superconducting Generators

Switching Surge Voltage Distribution in Superconducting Generators

Anomalous breakdown phenomena in PMMA immersed in transformer oil

The results of experimental investigations on anomalous breakdown characteristics of polymethylmethacrylate (PMMA) immersed in transformer oil under direct, alternating, lightning impulse ( 1.2 50 μ s ) and switching surge ( 250 2500 μ s ) voltage stresses are presented in this paper. The effect of waveshape and polarity of the applied voltage, thickness and size of the specimen and diameter of the high voltage electrode on anomalous breakdown are discussed.

Response of Transformer Windings to System Transient Voltages

Some recent transformer failures have been attributed to part-winding resonances excited by a form of switching surge voltage pulse which produced internal overvoltages. This paper takes a tutorial approach to relate a transformer winding to an equivalent electrical network which can exhibit resonant effects both at its terminals and internally. The relationship between the resonance phenomenon and pulse response is explained and illustrated with practical examples for the standard test waveforms. A proposed alternative switching surge waveform is examined for its effect on the internal response of transformer windings. The material presented should promote the understanding required for consideration of changes in standard test waveforms.

Switching Surge Flashover Characteristics of Long Disk Insulator Strings Under Polluted Conditions

Switching surge voltage tests were conducted on 280- by 170-mm standard-type disk insulator strings, and on 320-by 170- mm deep-rib-type disk insulator strings of 3.5 to 7.5 meters in length, under artificially polluted conditions.

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.

Surge Protection for Pipeline Motors

Recent field tests on motors in service on pipelines and powerhouse systems have shown that the switching surge voltage appearing at the motor terminals during initial energization for starting frequently reach magnitudes approaching 2.0 per unit normal crest line-to-ground operating voltage with time-to-crest as short as 0.2 As. This is more severe than normally believed and may endanger turn-to-turn insulation.

The Effect of Test and Abnormal System Voltages on Transformer Insulation

In service, a transformer will be subjected throughout its life to three different types of voltages. These are: power frequency, switching surge, and impulse voltages. Recent computer studies and field investigations of EHV systems have provided data on the magnitudes and durations of these voltages. Laboratory tests and factory tests of transformer insulator structures have provided new data on performance. Impulse test levels have been defined for many years. Modern lightning arresters can be selected to provide adequate protection against switching surges.

Flashover Characteristics on Insulators covered with Snow

This report describes flashover characteristics of the insulatorstrings and the rod-plane gaps covered with snow by switching surge and standard impulse voltage. From the various tests, it is shown that switching surge withstand voltage of a suspension string whose surface is covered with snow, is extremely lower than that under dry clean conditions about 50% ones.

Minimum Phase-to-Phase Electrical Clearances for Substations Based on Switching Surges and Lightning Surges

One method has been developed for estimating phase-to-phase clearances to withstand switching surge voltages and lightning surges in substations. Consideration has been given to the simultaneous occurrence of opposite polarity switching surges on adjacent phases, and propagating characteristics of lightning surges on the transmission lines.

Switching Surge Sparkover Characteristics of Air Gaps and Insulator Strings Under Practical Conditions

Sparkover characteristics of rod-rod gaps and insulator string by switching surge are presented under the following conditions: 1) With simultaneous application of switching surge voltages to both electrodes of a rod-rod gap. 2) With application of a switching surge voltage of the upper electrode in synchronizing to the peak of 50-cycle voltage which is continuously applied to the lower rod. 3) With surfaces of post insulator stacks and suspension insulator strings covered with snow or ice. 4) With surfaces of suspension insulator strings contaminated by salt.

Switching Surge Test Results EHV Substation Bus Configurations

Results of an extensive switching surge test program on extra high voltage substation bus arrangements are presented. Emphasis was placed on obtaining wet positive switching surge data under careful control of laboratory and analytical procedures. Evaluations are made of the switching surge characteristics of the air gaps for a variety of EHV bus arrangements. Involved are the effects of the dispersion for large air gaps on switching surge withstand levels and ranges of absolute crest switching surge voltage values that are to be expected. The air gaps between the several arrangements tests and the EHV data from other sources are compared.

Interim Report-Minimum Electrical Clearances ror Substations Based on Switching Surge Requirements

A method has been developed for estimating line-to-ground and phase-to-phase clearances to withstand switching surge voltages in substations. Clearances have been calculated for standard system operating voltages through 500 kv with an assumed switching surge magnitude of 2.8 times the maximum line-to-neutral crest voltage. Consideration has been given to the simultaneous occurrence of opposite polarity switching surges on adjacent phases. Clearance values will be verified by testing programs before being recommended for design purposes.

Effect or Preceding Bias Voltage on Switching-Surge Operation of Spill Gaps and Lightning Arresters

Line-dropping tests on the Southern California Edison Company system showed that previously encountered spill-gap operation was not caused by extremely high switching-surge voltages, but by abnornally low sparkover of bushing-mounted gaps. In some cases lightning arresters also operated at abnormally low switching-surge voltages. Laboratory tests showed that a nonuniform gap field and trapped charges on the adjacent porcelain surface rendered spill-gap sparkover susceptible to wave front steepness and, particularly, to preceding voltages of opposite polarity. A gap located remotely from porcelain surfaces was found to be relatively free from these effects.

Probability Method for Determining Insulation of EHV Lines

A probability method is presented for the design of clearances and number of insulators for extra-high-voltage (EHV) lines. The method involves determination of a tolerable probability of flashover for critical switching operations and the corresponding switching-surge voltages. The probabilities of flashover for various insulation designs are then calculated from data on wind, conductor swing, climatic, and insulation-strength probabilities. From these, the adequacy and economics of the insulation design can be determined.

Switching Surge Voltages Due to the Interruption of Transformer Magnetizing Current

Switching Surge Voltages Due to the Interruption of Transformer Magnetizing Current