Etsunori Mori

Optical Voltage and Current Measuring System for Electric Power Systems

Recently, optical voltage and current measuring methods based on a principle different from that of the existing apparatus have been developed. As the most promising method among them, a voltage measuring method which uses an electrooptic effect called the Pockels effect and a current measuring method which uses a magnetooptic effect called the Faraday effect have been proposed. The authors have developed an optical voltage measuring system based on the electrooptic effect in bismuth germanium oxide Bi4Ge3O12 and a current measuring system based on the magnetooptic effect of borosilicate crown glass for the purpose of utilization in electric power systems. As a result of the development, high accurate voltage and current measuring systems such as non linearity error less than ±0.4% and temperature stability less than ±1.0% were obtained. Furthermore, short-circuit current was measured with the current measuring system, and an accuracy within 0 to -4% in the range of 30 kApeak to 150 kApeak was obtained. When the measuring systems were mounted on the model of 70 kV class gas insulated switchgears, it was verified that the measuring systems had satisfactory linearity and temperature stability.

Niew Apparatus for Detecting Transformer Faults

A diagnostic apparatus for detecting gases dissolved in transformer oil is described, in which a tetrafluoroethylene-perfluoroalkylvinylether copolymer membrane is used to separate H2 CO, CH4, C2H2, C2H4, and C2H6 from the oil. These gases are detected with a new gas detector, which consists of a catalytic gas sensor and a gas chromatograph using air as the carrier gas. Using the gas concentration, the apparatus automatically determines whether a transformer is operating normally or not and, in the latter case, what kind of fault may have occurred. By the above diagnostic apparatus, a transformer could be diagnosed simply and inexpensively. This apparatus should prove useful for identifying what kind of fault may have occurred.

New Apparatus for Detecting H2, CO, and CH4 Dissolved in Transformer Oil

This report presents a new method of separating H2, CO, CH4, C2H2, C2H4, and C2H6 dissolved in transformer oil and detecting H2, CO, and CH4, in which a tetrafluoroethylene-perfluoroalkylvinylether copolymer membrane is used to separate gases from the oil. The quantities of H2, CO, and CH4 that permeated through the membrane were relatively large. These gases were detected with a new gas detector, which consists of a catalytic gas sensor and a gas chromatograph, and which uses air as the carrier gas. Compared with conventional methods of gas analysis, H2, CO, and CH4 dissolved in transformer oil can be analyzed simply and inexpensively with this method. As a result, this new method should prove useful in determining whether a transformer is operating normally or not.

Apparatus for Continuously Monitoring Hydrogen Gas Dissolved in Transformer Oil

This report presents an apparatus for continuously monitoring of hydrogen gas dissolved in transformer oil, in which a polyimide membrane is used to separate the hydrogen from the oil. The hydrogen is allowed to permeate through the membrane and contact a gas sensor every 72 hours. The characteristics of the permeation of the hydrogen gas through the polyimide membrane and of the detection of the hydrogen gas by the gas sensor are described under various conditions. Problems encountered when the apparatus is installed on a tran are also studied and solved. As a result, this new apparatus was found useful in determining whether a transformer is operating normally or not.

Development of an Optical Current Transformer for Adjustable Speed Pumped Storage Systems

The design and testing of a passive optical current transformer utilizing the Faraday effect is described. The optical current transformer (OCT) was developed to measure the rotor excitation current of a 400 MW adjustable speed pumped storage system. Overall dimensions of the bulk optic sensor are 250/spl times/250/spl times/40 mm and the OCT functions as an overcurrent sensor to a maximum current 35000 A/sub p/. This OCT has been practically applied at the Ohkawachi Power Plant of the Kansai Electric Power Co., Inc. since December 1993.

Development of a Prototype UHV Transformer and its Application to 500 kV Transformers

Development principles of an insulation structure for a prototype UHV transformer are presented. New interleaved windings having gradual apportionment of series capacitances were developed, and shown to have approximately uniform voltage distribution for lightning impulse and high reliabaility in their dielectric characteristics. The insulation structure developed for the UHV transformer was applied to a 500 kV transforrner, which allowed its floor space, weight and loss to be reduced about 20 % compared to a conventional 500 kV transformer.

A diagnostic method based on RVM (return voltage measurement) for condenser bushings with oil–paper insulation systems

The bushing of a transformer is one part of the transformer system, but is as vital as the transformer itself because it forms a part of the main circuit. Deterioration and abnormal condition of the bushing possibly cause its destruction, shortage of the main circuit to the Earth, and fire in the systems, so that diagnosis of the bushings is thus very important. At present, mainly visual inspection from outside of the bushing is carried out. Inspection of the inside condition of the bushing by dissolved gas analysis of the inside oil is done only as sampling for selected bushings because it is difficult due to the sealed construction of the bushings. Therefore, a simple diagnostic method for bushings has been expected for a long time. In Eastern Europe, the RVM (Return Voltage Measurement) method based on scanning the polarization spectra was applied to the oil–paper insulation systems inside the transformer as a diagnostic method. In this paper we investigate theoretically the principle of the RVM method applied to bushings with the same oil–paper insulation systems as the transformer by using the equivalent circuit, and the possibility of using this novel diagnostic method for condenser-type bushings is demonstrated by a model experiment.