Wa van der Linden

Disconnector switching in GIS: three-phase testing and phenomena

Certification tests in accordance with the requirements of the recent IEC 61259 standard for switching of bus-charging current by disconnecters of a (three-phase enclosed) 145 kV gas insulated switchgear (GIS) are described. These tests are primarily aimed at verifying that the discharge between the disconnector contacts does not introduce internal arc faults. Special emphasis is given to the high-frequency measuring system, used to verify a sufficiently severe waveshape of switching transients in the MHz range. Three-phase tests were performed, showing phenomena that were not demonstrated in practice before: first, it was shown that phase-to-phase voltage transients with a higher amplitude than the phase-to-ground values do actually occur. Second, the phase-to-phase capacitive coupling of the busbar system could raise the trapped charge, left after at the load side of the installation after disconnection, to values above 1 pu. In addition, measurements of induced voltages in the secondary system are reported.

The testing of SF/sub 6/ generator circuit-breakers

Generator circuit-breakers face much higher current and voltage stress than distribution switchgear. This has led to a special standard (ANSI C37.013). Strictly in accordance with this standards requirements, test circuits and parameters for a 100 kA and 120 kA (25.3 kV) SF/sub 6/ generator circuit-breaker have been defined. The circuit-breaker is equipped with capacitors at both sides of the extinction chambers. The effect of these is to reduce the TRV severity and this is quantified for the relevant switching duties. Adequate test-circuits are described. Also, the optional verification of interruption of generator-fed faults with very large DC components has been demonstrated. Herein, delayed current zero can extend arcing time. The importance of arc voltage in reducing the longer arcing time is illustrated in a calculated example.

A New Artificial Line For Testing High-Voltage Circuit Breakers

In a high-power laboratory, artificial lines are used for short-line fault testing on high-voltage circuit breakers. Over the years, several different configurations of artificial lines have been designed and used in testing laboratories. This article describes an artificial line for testing circuit breakers with current ratings up to 100 kArms. The artificial line combines constructional advantages with good practical results and has been successfully in use in KEMAs High-Power Laboratory since 1978.

Verification of the Short-Circuit Current Making Capability of High-Voltage Switching Devices

Switching in of short-circuit current leads to pre-arcing in the switching device. Pre-arcing affects the ability of switchgear to close and latch. In three-phase systems, making is associated with transient voltage phenomena that may have a significant impact on the duration of the pre-arcing period. An analysis of these transients is presented. It was found that pre-arcing times in three-phase systems can be considerably prolonged with respect to a single-phase situation. On the other hand, it is demonstrated that the three-phase interaction has a moderating influence on the peak value of asymmetrical current. A test circuit is described, able to perform three-phase synthetic make tests up to 245 kV at current up to 63 kA, representing all transient phenomena. Specific tests are described requiring the maximum available laboratory power: one with a circuit breaker subjected to direct test and one with a high-speed grounding switch subjected to synthetic tests.

A Three Phase Synthetic Test-Circuit for Metal-Enclosed Circuit-Breakers

Metal-enclosed circuit-breakers with all three phases in a common enclosure are used when a compact and economical substation lay-out is required. The three interrupters influence each other during the interrupting process. According to the latest IEC-Standard, three phase testing is necessary to cover all possible interactions between the interrupters. Several test methods and test circuits have been proposed and used in the past. This paper describes a synthetic test circuit for three phase tests, which has been used with success since 1981. It can be used to test metal-enclosed circuit-breakers with a rated voltage up to 300 kV. The results of tests on a 145 kV - 40 kA three phase GIS are presented.

Magnetic saturation at short-circuit tests on power transformers

The post-set and pre-set short-circuit test methods for power transformers are discussed. KEMAs testing experience with special attention to the pre-set method, inrush currents and premagnetization, are highlighted. By means of premagnetization inrush currents can be avoided to a large extend The saturation of the supply side transformers leads to a distortion of the supply side voltage, thus preventing saturation of the test objects. The different saturation modes of the transformer under test are briefly mentioned in relation to the dynamic stresses on the windings.

Short Circuit Testing Methods for Generator Circuit Breakers with a Parallel Resistor

ANSI-Standard C37.09-1979 describes design and testing of AC high voltage circuit-breakers under fault conditions. For synthetic test methods application guide ANSI/IEEE C37.081-1981 is added. Presently, generator circuit-breakers of the airblast type are built with a low ohmic parallel damping resistor. At this time there are no standards establishing test circuits or test procedures for this type of circuit-breaker. This article outlines the problems involved in testing generator circuit-breakers equipped with parallel resistors and gives a qualitative analysis of several test circuits.