Susumu Nishiwaki

Suppression of VFT in 1100 kV GIS by adopting resistor-fitted disconnector

With 1000 kV transmission lines planned in Japan, very fast transient (VFT) phenomena will be suppressed by installing a resistor in a disconnector of gas insulated switchgear (GIS). In this paper the VFT overvoltage suppressing effect of the resistor and the duty required of the resistor are clarified. A 1100 kV resistor-fitted disconnector was tested by constructing a charging current interruption test circuit. It has been clarified that the disconnector accepts the required duty. The disconnector tested is used for the field test.

Estimation of Restriking Transient Overvoltage on Disconnecting Switch for GIS

On an actual 550kV GIS (gas-insulated switchgear), the restriking surges of disconnecting switches at a high frequency of several MHz were successfully measured by employing two different methods. Further, by comparing the measured waveforms with waveforms obtained through calculations, it has been proved that restriking surge of disconnecting switches can be estimated by conducting calculations with considerably high accuracy. Also included, in this paper are certain suggestions regarding GIS simulation methods to be adopted for the calculations, while concurrently reported are the results of calculations on 111 circuit configurations at 10 different GISs.

DC current interruption in HVDC SF/sub 6/ gas MRTB by means of self-excited oscillation superimposition

The Kii-Channel HVDC Link under construction in Japan is equipped with metallic return transfer breakers (MRTBs) in one converter station. A new MRTB for an interrupting current of 3500 A DC was developed. To interrupt a DC current, a method that produces a current zero point by superimposing a self-excited oscillatory current on a DC arc current was employed. For this purpose, a LC circuit was coupled in parallel to a SF/sub 6/ gas circuit breaker. Developing a SF/sub 6/ gas circuit breaker that has a large arc voltage drop gradient against currents permitted a large oscillatory current to be generated. A modified Mayr-type dynamic arc equation was newly presented. The DC interruption limits calculated using this equation agreed with the measured values.

Computation of Arrester Thermal Stability

Full-scale thermal stability type tests on substation class metal oxide arresters are not practical. As a result, standards such as IEC 60099-4 specify the use of a reduced-scale model and define test methods which are intended to assure that the reduced-scale model is conservative relative to the full-scale arrester. The authors succeeded in computing the thermal stability of full-scale arresters based on the operating duty arrester type test specified in IEC60099-4 and ANSI in a few hours using transient nonlinear finite element software customized for the purpose. Based on these computations, the cooling mechanism of a polymer arrester and the effect of arrester structure on thermal stability could be evaluated. The authors are continuing this approach with the expectation of achieving more accurate prediction of full-scale arrester stability computationally than can be achieved using reduced-scale models. The present paper contributes to the understanding of appropriate reduced-scale models, their relationship to the thermal stability of full-scale arresters, and how to define the thermal stability of a full-scale arrester.

Surge Discharge Capability and Thermal Stability of a Metal Oxide Surge Arrester

The surge discharge capability and the thermal stability of a metal oxide surge arrester were examined experimentally.

Development of 800 kV gas-insulated switchgear

An 800 kV gas-insulated switchgear, with a capacity level recognized as the largest in the world, was developed as the first development of UHV gas-insulated switchgear, and good results were obtained in the type tests for this switchgear. With the gas circuit breaker and the disconnector used in this gas-insulated switchgear, tests on a scale innovative from a global viewpoint were carried out. Taking recent research into account, test methods were renovated. The long-term reliability of all insulators was demonstrated by submitting them to long-term voltage and current tests. Finally, measuring surges due to the switching of a disconnector and a shunt reactor on the equipment installed at the site, it was verified that measured and calculated values agreed. >

Study of Thermal Runaway/Equivalent Prorated Model of A ZnO Surge Arrester

Zinc-oxide surge arresters experience thermal runaway when the temperature rises beyond the permissible limit. This phenomenon is created by increased leakage current resulting from a resistance drop of ZnO elements in the low current region which occurs along with the temperature rise.

Effects of hot SF/sub 6/ on post-arc circuit breaker design

SF/sub 6/ is blown through the arc during interruption of an SF/sub 6/ puffer circuit breaker. This hot gas flows down an exhaust tube into the chamber of a dead tank circuit breaker where it can lower the dielectric withstand between the exhaust tube and the tank of the circuit breaker, leading to dielectric breakdown during the transient recovery voltage after clearing. This paper presents experimental evidence that any such breakdown is controlled by the hot gas near the exhaust tube, with cold gas in the remainder of gap having little effect on the breakdown voltage. This experimental conclusion is supported by a detailed theory for conditions under which breakdown can occur.

Reignition surges at reactor current interruption in cable-system GIS

A 150 MVA reactor current interruption test using a GIS (gas-insulated switchgear) on an actual 275 kV cable system and a laboratory high-frequency current interruption test using a 300 kV SF/sub 6/ gas circuit breaker were conducted. The results of these tests and their analyses, made simultaneously, permitted (1) the calculation of reignition surges and the detection of high-frequency arc extinctions caused when the reactor current was interrupted by a GIS on a cable system and (2) an evaluation of voltage escalation caused at high-frequency arc extinctions. >

Electromagnetic interference with electronic apparatus by switching surges in GIS-cable system

Thyristor malignitions and protector relay failures caused by gas circuit breakers closing in the gas insulated switchgear (GIS) of a power cable system could not be controlled by reducing the ground impedance or adding surge absorbing capacitors. As a result, a study was carried out on this problem with a 66 kV mock-up apparatus installed in a factory. It was found that malignitions and failures such as those mentioned above could be controlled by preventing 10 MHz ultra high-frequency surges emitted by the GIS from leaking out into the grounding system. >