Shingo Shirakawa

Maintenance of surge arrester by a portable arrester leakage current detector

An instrument is described that detects leakage current without disconnecting the arrester ground wire. Better means were developed for detecting deterioration of a surge arrester than the existing appearance inspection, insulation resistance measurement, and leakage current measurement. The device measures only the in component of the current, which is proportional to the power loss. The change of the latter is the recognized measure of deterioration. >

Influence of Uniformity on Energy Absorption Capabilities of Zinc Oxide Elements as Applied in Arresters

This paper describes electrical uniformity of the zinc oxide nonlinear resistor element (ZnO element) used for ZnO arresters. A simple and useful method for the uniformity evaluation makes use of thermography, obtained by an infrared radiation thermo-camera, of the metallized surface. Relationships between uniformity and energy absorption capabilities were obtained experimentally.

Improved zinc oxide surge arresters using high voltage gradient 300 V/mm, 400 V/mm ZnO elements

Zinc oxide surge arresters using zinc oxide (ZnO) elements have been widely used for insulation coordination in the worlds power systems. These ZnO elements have basically reference voltage of about 200 V/mm. Recently, new ZnO elements having about 1.5, 2 times high voltage gradient zinc oxide element have been developed. This paper describes applications of high voltage gradient 300 V/mm ZnO elements to high performance porcelain type surge arresters and oil immersed surge arresters, and 300 V/mm or 400 V/mm ZnO elements to gas insulated tank type surge arresters for power systems. Adequate selection of voltage gradient of ZnO elements makes more compact design of the surge arresters.

Power dissipation characteristics of zinc-oxide arresters for HVDC systems

The voltage waveforms applied to HVDC surge arresters do not have a simple sinusoidal shape, so that the leakage current contains high-frequency components. The power dissipation characteristics of a thyristor valve arrester were measured using a 1/25 prorated arrester section with a 5 kV/500 kW thyristor bridge. High-frequency power dissipation characteristics of the zinc-oxide elements were measured, and it was found that the high-frequency power dissipation of the thyristor valve arrester is larger than that of an AC system arrester. The determination of the equivalent continuous operating voltage for the performance testing of an HVDC arrester is considered. >

Application of high voltage gradient zinc oxide elements to SF/sub 6/ gas insulated surge arresters for 22 kV-765 kV power systems

Zinc oxide elements have been developed for the surge arrester elements. Basically, these zinc oxide elements are evaluated by the reference voltage V/sub N/mA. Newly developed high voltage gradient zinc oxide elements have about twice value V/sub N/mA/mm of normal zinc oxide elements. This paper describes the application of the high voltage gradient zinc oxide elements to SF/sub 6/ gas insulated tank type surge arresters for 22 kV-765 kV power systems.

Application and development of a ceramics resistor for use as a neutral grounding resistor (NGR)

A super-compact SF/sub 6/ gas insulated neutral grounding resistor (NGR) is presented that uses recently developed high-power resistors made of a novel ceramic material. The microstructure, voltage-current characteristics, and current-carrying characteristics of the resistor element are examined. The composition and features of the NGR are discussed. >

Relation of insulation resistance and deteriorated ratio of reference voltage of oil-immersed surge arrester elements enclosed in pole transformers

About ten years have passed since oil immersed surge arrester elements enclosed in 6.6 kV pole transformers were first used. At present, technical developments are being demanded to judge the soundness of these oil immersed surge arrester elements by a simple method, allowing one to judge easily whether these elements can be used or not onsite. The authors empirically investigated the correlation between the insulation resistance and the deteriorated ratio of the reference voltage of these oil-immersed surge arrester elements. It was found that the deterioration of the oil-immersed surge arrester elements can be detected by measuring the insulation resistance.

Evaluation and application of oil‐immersed zinc oxide elements enclosed in pole‐mounted distribution transformers

Voltage due to lightning surge is now a major problem to be overcome to ensure full reliability of any power supply. Hence, gapless oil-immersed surge arresters using zinc oxide elements have been applied to pole transformers. These surge arresters are used as a means of insulation coordination for pole transformers. These arresters contribute to the reduction of the number of failure of pole transformers. This paper describes applications and effects of specially developed oil-immersed surge arresters in pole transformers on 6.6-kV distribution lines.

Operating duty test of surge arresters for HVDC transmission systems

An operating duty test of a high-voltage (64 kV) dc arrester was performed in the field. The results obtained were compared with those of a laboratory test on a prorated section of thec same arrester (8 kV). This comparison demonstrated the validity of the equivalent prorated test method. In another operating duty test conducted under the severe condition of deblocking with full rectifier voltage against an open inverter end, the operating capabilities of a prorated section were demonstrated.