Guy St-Jean

Empirical model of a current-limiting fuse using EMTP

An empirical model is discussed for research on current-limiting (CL) fuses used in distribution system applications. The main characteristic of a CL fuse is that it develops a voltage at its terminals which reduces the amount of energy generated in the protected equipment during a fault. The various stages of fuse operation are modeled using electric components. The model is of limited use, but its simplicity enables a nonexpert to use it without spending months to learn and program a sophisticated model. The model makes it possible to establish which closing angle of source voltage will produce the greatest of I/sup 2/t, assuming a melting time shorter than a quarter of a cycle. The model can also show how the let-through value of I/sup 2/t will be influenced by the voltage versus time profile of the fuse voltage. The electromagnetic transient program, EMTP, proved a useful tool for this development. >

Nuisance fuse operation on MV transformers during storms

The authors report on producing in a laboratory a sequence of events leading to nuisance operation of fuses on distribution transformers during thunderstorms. It is observed that such nuisance operations can be caused by long (a few milliseconds) low-amplitude (less than 1 KA) current passing through a surge arrester, causing overvoltage and saturation of its protected transformer and an inrush current that blows the fuse without a fault situation. An experimental sensitivity analysis was performed by varying the surge arrester, transformer, and fuse involved. In general, new ZnO-based arresters, which produce a higher voltage than SiC-based arresters at impulse currents below 1000 A, will result in a higher transformer inrush current and greater likelihood of nuisance fuse blowing. >

Pressure Relief Design and Performance of Metal Oxide Surge Arresters

Surge arresters with porcelain housing must not have explosive breakage of the housing to minimize damage to other equipment when subjected to internal high short circuit currents. Also, arrester porcelain housings are generally susceptible to undesirable thermal shock. As a solution, this paper describes pressure relief design and performance of arresters equipped with a fiber reinforced plastic tube and an optimum pressure relief nozzle. The arresters showed satisfactory performance during a newly developed synthetic pressure relief test using a 25 kA symmetrical rms current with the first half-cycle fully offset.

Comparison of ANSI, IEC, and CSA standards' durability requirements on station-type metal oxide surge arresters for EHV power systems

An analysis of stresses applied to two types of station class surge arresters of the same voltage rating when tested for durability as prescribed by American (ANSI), International (IEC), and Canadian (CSA) standards for 315 kV and 735 kV power systems is presented. The analysis, which is made with an experimentally validated arrester model, reveals that the IEC duty cycle test is the most severe of all. It can bring the varistors of an actual station-type arrester to a peak temperature of 129 degrees C, which leaves a margin of only 46 degrees C to its thermal stability limit at maximum continuous operating voltage. Another actual arrester using lesser V-I-T varistor characteristics but larger varistor volume and better heat transfer from inside to outside the arrester produces 103 degrees C, which corresponds to a slightly better temperature margin of 49 degrees C. It is observed that, even when using the lower-performance V-I-T characteristics of the latter arrester, a thin-wall arrester housing design can improve heat transfer to a point where the margin improves to 101 degrees C on a hypothetical arrester. >

A Method for Calculating Directly the Components of a Synrhetic Circuit for the Testing of AC Circuit Breakers

A method for calculating the components of a synthetic circuit for the testing of ac circuit breakers is presented.

Comparing direct and synthetic tests for interruption of line-charging capacitive current

Using a validated arc model, this paper analyzes current distortion and voltage waveforms during both direct and synthetic tests for interruption of line-charging capacitive current by power circuit breakers. Although the voltage of the electric arc drawn between breaker contacts may produce significant current distortion, it is demonstrated that the most significant parameter affecting the breaking capacity of power circuit breakers in capacitive-current switching tests is the voltage jump appearing across breaker contacts immediately after current interruption. It is essential to correctly define the supply circuit impedances and the associated voltage jump so as not to reduce or increase this test severity unduly.

Comparison of waveshape quality of artificial lines used for short-line fault breaking tests on HV circuit breakers

The authors present a comparison of the waveshape quality of six different artificial-line circuits used to produce the high rate-of-rise of recovery voltage specified by ANSI and IEC standards. For a purely capacitive and inductive pi-section circuit, it is shown that even eight pi sections do not meet the requirements. With the addition of a resistance in the first branch, this circuit design produces adequate solutions but requires a large number of components. The analysis reveals that the KEMA circuit easily meets the requirements for the rated peak factor of 1.6 but for the 1.8 peak factor a compensation would be required for the initial part of the wave. The simplest circuit comprising only three (RLC) components meets the specifications with a high voltage-peak overstress factor of 1.3. >

A 2-MV 4.5-MJ Synthetic Test Source for HV Circuit Breakers

This paper describes IREQs synthetic test source, which underwent commissioning tests in July 1983. Its unusual physical and electrical characteristics are given along with a description of its fully computerized operation. This source has already been used for six different types of test. Tests on full poles of 735-kV circuit breakers as well as on metal-oxide surge arrester sections intended for a 735-kV transmission system were performed.

Comparison of the capabilities of metal oxide and conventional high voltage surge arresters

Abstract The aim of this paper is to draw a comparison between conventional and metal oxide arresters in order to familiarize the surge arrester user with their operating characteristics. Their protective level and durability features are compared in some detail and a simple mathematical model of their voltage-current characteristics is proposed to facilitate the task of selecting suitable arresters for a given system.

A validated high-voltage arrester model for transient network analyzer applications

Abstract This paper describes the development of a dynamic surge arrester model for use on a transient network analyzer to evaluate the arrester instantaneous voltage, current and total energy during conduction. Based on the results of duty-cycle tests, a model is proposed for which three sets of parameters were found to match three different makes of 72 kV arrester. The relative values of these parameters are discussed as well as a general set of parameters that could represent all three types of arrester.