Mitsuhito Kamei

Partial discharge diagnosis method using electromagnetic wave mode transformation in gas insulated switchgear

Though the gas insulated switchgear (GIS) insulation diagnosis method using ultra high frequency (UHF) band signal is widely used as a method to detect partial discharge (PD) sensitively, diagnosis methods for the electromagnetic wave mode propagation behavior in GIS tanks have not been investigated enough. Especially, diagnosis methods based on the electromagnetic wave distribution of the circumferential direction have been rarely discussed. In the preceding studies by the authors comparing investigations were made by experiments and analyses on the electromagnetic field distribution patterns of the GIS circumferential direction in front of or behind the L-shape or T-shape structures. It was found that the electromagnetic field distributions that are characteristic of mode transformations are seen when the electromagnetic waves of the PD signals are propagated through the L-shape and/or T-shape structures in the GISs. In this study, the diagnosis algorithm is constructed by extracting the characteristics in the output of the high order mode electromagnetic waves transmitted through the L-shape part and/or T-shape part. If the output distributions of the signals detected before and/or after the transmitting have those characteristics, the signals can be determined to be the ones propagated inside and the information on the circumferential direction position of the signal source can be obtained. A simple diagnosis method with high precision has been developed as a GIS-PD diagnosis technology in the field based on the diagnosis algorithm as above. The diagnoses in the field can be classified into the first order diagnosis for high sensitivity detection and the second order diagnosis for high precision judgment by using the algorithm to do more reliable evaluation.

Simulation of propagation characteristics of higher order mode electromagnetic waves in GIS

Numerical simulation of electromagnetic fields was performed to investigate the transmission and reflection characteristics of electromagnetic waves excited by partial discharge through spacers, L-shaped sections of a GIS bus structure. The resonance frequencies of a cavity between spacers agreed roughly with the experiment. The modes of electromagnetic wave are shown to transform to different modes, e.g., from TE11 to TE21 mode, after transmission and reflection through L-shaped sections of a GIS. The frequency intervals of the resonance in tanks longitudinal direction for a L-shaped section are different between horizontal and vertical excitation of partial discharge source. The two characteristics, mode transformation and the dependence of resonance frequency on excitation direction, were confirmed experimentally

Partial discharge diagnosis method using electromagnetic wave mode transformation in actual GIS structure

The diagnosis algorithm using ultra high frequency (UHF) method with the higher-order electromagnetic wave (EM-wave) was examined as the advanced partial discharge (PD) diagnosis method in a gas insulated switchgear (GIS) in the former paper. Previous studies evaluated the characteristics of EM-waves propagated in a simple coaxial cylindrical pipe, or through an L-shaped or a T-shaped pipe formed by combining these. In the present study, components (a hand hole, a post-type spacer, etc.) present in an actual GIS structure were identified, and an evaluation done mainly through an analysis on what effects their presence has on the mode transformation of EM-waves propagated inside a GIS tank. The direction in which a GIS tank is bent is horizontal (0deg) in the L-shape structure. If there is either a post-type spacer or a shield ring inside, and the signal source is in the 0deg direction, the distribution of the EM-wave strength varied according to through the L-shape structure. Also in the case of a T-shaped structure, the distribution of the output after signals are transmitted through the T-shaped junction varied depending on each component. Based on these characteristics, the diagnosis algorithm for PD with higher-order mode EM-waves was improved taking into account the effects of various components existing in an actual GIS, and a PD diagnosis method more suitable for an actual structure was established.

Development of SF6 decomposition gas sensor

Abstract Gas sensors for detecting SF6 decomposition products have been pursued as low-cost instrumentation for detecting and locating faults in gas-insulated switchgear (GIS). We have developed an amperometric solid-state ionic sensor using fluorine ion-conductive solid electrolyte. In order to improve its sensitivity, the surfaces of the electrolyte are roughened by sandblasting, and are covered with the gas permeable Au electrodes. The roughness of the surfaces and the thickness of the electrodes are optimized. It has been confirmed that the sensor responds promptly to 1 ppm HF gas at room temperature, and returns to its original level once the HF gas is removed.

Resonance characteristics and identification of modes of electromagnetic waves excited by partial discharges in GIS

Electromagnetic waves are used for detection of partial discharges (PD) in GIS (gas-insulated substations). A very wide frequency band up to 1.5 GHz is utilized for detection. There are three categories of electromagnetic wave which can be excited and propagate in coaxial cylindrical structures like GIS, namely, TEM, TE, and TM modes. The characterization and identification of each mode is indispensable to understanding the partial discharge phenomena in GIS. In this paper, peaks in the frequency spectrum excited by PD are identified in each mode and the resonant characteristics of each mode are studied. The following are the major results: (1) The resonance peaks appear at the frequencies defined by the spacer distance. (2) The intensity of each mode depends on the position of discharge source along the radial direction. The lower-order modes including TEM are excited when a discharge source is located near the center conductor. On the other hand, higher-order modes are excited when the discharge source is at the enclosure surface. (3) The experimental profile of each mode excited by PD along the radial direction approximately agrees with the general theory of electromagnetic wave propagation in coaxial cylindrical cavity.

On-Line Monitoring Of Surface Roughness By Using Laser

This paper deals with a basic research on an on-line monitoring of surface roughness by using laser. The relation between an intensity distribution of the reflected laser light and the surface profile is studied. A function of the processed r.m.s. roughness is used, which is taken from the spatial filtering of the surface profile measured by stylus method. An experiment was carried out by using a rolled metallic sheet and pieces finished by an electrical discharge machine. The results show that the intensity distribution is approximately proportional to the r.m.s. roughness of a certain filterd surface profile. The experimental results are proved to be reasonable by theoretical analysis.

Insulation characteristics of epoxy insulator with internal crack-shaped micro-defects - study on the equivalence of accelerated degradation by frequency acceleration test

Generally, insulating spacers of gas insulated switchgear (GIS) have outstanding durability and are not considered prone to insulation failure within a design life of about 30 years, provided the products conform and have passed the partial discharge (PD) test. However, to assume operation over 30 years, degradation characteristics are important in cases where an extremely microscopic defect below the detection level in the PD test is present or produced inside the insulator. Accordingly, to date, the authors have obtained the breakdown voltagetime (V-t) characteristics using epoxy insulators provided with three types of micro-defect (crack, void, and delamination); the apparent PD of which is equivalent to 1 pC for an actual 550 kV-GIS spacer. It emerged based on these V-t characteristics that the breakdown risk peaked for a crack defect among those three types of shape and that it was essential to obtain data on long-term breakdown characteristics at the actual operating electric field level to rigorously evaluate the breakdown risk under long-term operation. Therefore, this paper includes a study on the equivalence of accelerated degradation by frequency acceleration as a means of determining the long-term breakdown characteristics. In the study, the dependency of various PD characteristics on frequency was initially examined by changing the frequency of the applied voltage within the range 60 to 3000 Hz. Consequently, the increase in the number of PDs per unit time proportional to frequency could be confirmed without any abnormal phenomena, such as suspended discharge, observed within the frequency range this time. In other words, it was clarified that the degradation due to PD could be accelerated by increasing the frequency. Subsequently, breakdown tests were conducted with frequency as a parameter to evaluate the frequency up to which the equivalence of accelerated degradation could be maintained based on breakdown times. As a result, it was found that the equivalence of acceleration degradation by frequency acceleration was valid in acceleration at up to 1500 Hz because the breakdown time was shortened in reverse proportion to the frequency.

Development of optical travel sensor for power circuit breaker

A travel sensor detects a motion of a mechanical part of a circuit breaker and checks its condition of the operation mechanism. We have developed a new optical travel sensor which measures a motion of a sealing rod with no contact. The design of the travel sensor and its fundamental inspections will be mentioned in this report. In our proposed sensor, the silhouette of the sealing rod is detected optically, and the motion of the rod is detected with no contact. Using optical fiber sheets, electric components such as the light source, the image sensor, and signal processing circuits are located remotely from the circuit breaker. As a result of this construction, the sensor is not affected by electro-magnetic noise. The travel sensor is constructed with two mirrors retro-reflecting illuminating light and prisms inverting the rod image. It is easy to adjust the mirrors according to the retro-reflecting construction. As the prisms compensate for the inverting effect of the lenses, intensity fluctuation of the rod image decreases. As a result of our fundamental inspections, we confirmed that the travel sensor had the detected range of 125 mm and the position resolution of 1 mm.

A Vapor Leak Sensor Using Polarization Property For Plant Inspection

This paper deals with the development of a vapor leak sensor for plant inspection. The sensor requires the ability to selectively detect troubles in various circumstances. The method to detect vapor leak is based on the detection of scattered light. The experiment on polarization property shows that there is large difference between the scattered light from vapor and that from structures in a plant, and that the method is effective for the distinction of the two scattered lights. As a result of our experiment, it is confirmed that the sensor enables us to selectively detect the vapor leak with high sensitivity even in a plant and has high performance for plant inspection.

A simplified visual inspection system using a personal computer

For a practical visual inspection system, data processing in real time, flexibility for variety of products, and cost performance have been required. This article describes a simplified visual inspection system that has well-balanced performance that meets these requirements. Inspection data processing by software makes the inspection system flexible. Development of a simplified pattern matching method based on limiting the inspection within the area pointed by an user and direct memory access of binary image data performs a high speed inspection function. By using a personal computer as a processor of this system, a cost effective inspection system is realized.