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In recent years, “asset management” or “managing assets” technique has been expected to rationalize maintenance and operation of electric power equipment, especially for aging equipment. Some concrete support tools have been developed by considering life cycle cost for substation equipment in “Central Research Institute of Electric Power Industry, Japan,” which include failure risk evaluation. Such cost and risk evaluation are essential for comparative evaluation of different types of equipment. Failure probability is one of the most important factors for the evaluation. Because of its high reliability, electric power equipment can be expected to have a very long lifetime, therefore, durability test is not applicable, but rather relies on analysis of actual operational data. Collection, accumulation, and analysis of actual operational data are necessary for accurate evaluation. This chapter describes the evaluation method for the managing assets, and data collection and analysis to improve the accuracy of failure probability estimation.

The asset management technique, which was developed in the field of financial engineering, is expected to rationalize business operations. There have been some previous investigations on introducing this technique into the maintenance divisions of electric power transmission and distribution facilities in Europe. Therefore CRIEPI (Central Research Institute of Electric Power Industry) is examining its effective introduction into Japan in the last about 15 years by referring to these investigations. In this paper, the evaluation is in terms of cost. Two types of cost, the maintenance cost in ordinary operation and the failure-handling cost including a penalty cost of electric outage, are considered in this investigation. The basic concept and a support program used to select better maintenance scenarios for an oil-immersed power transformer are described in this paper. The candidates are the successive operation of aged equipment by repairing it whenever possible or by large-scale repair (overhaul) until expected lifetime, and replacement by new, low-maintenance-cost equipment immediately or at a certain age. The cumulative maintenance cost is calculated for each scenario as the NPV (Net Present Value). In replacement scenarios, the depreciation is considered for realism. At present, the maintenance cost characteristic and the failure probability by age, which should be input to the support program as parameters, are under investigation. The method and difficulties are also described.

The XLPE power cable has been widely used in power transmission and distribution system since middle 1960’s, and many of them in 60 kV class grid under present operation was laid till mid 1980’s to the end of 1990’s. Their age is reaching their designed lifetime of 30 years or exceeding it, and the grid system operators require information of electrical insulation capability of their XLPE cables. This paper firstly reveals the insulation capability of such aged 60 kV class XLPE cable by the pre-breakdown discharge detection testing techniques. Then, it is clarified that the water tree is dominant degradation cause of such XLPE cables even manufactured by dry-cured and threelayer simultaneously extruded processes, which are considered to avoid water tree generation and development.

Application of Bayes' theorem for the evaluation of diagnostic results of electric facilities is described. A concept of risk assessment method based on the diagnosis results is proposed and the effects of various parameters on the risk are clarified. Based on these results, a rational renewal scheme using diagnostic results is proposed. In addition, the prior probability based on the data of actual facilities is investigated and it is found that the data available so far is insufficient and more data are required for the detailed analysis. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Spectroscopic and imaging analyses using electromagnetic waves in the far IR or submillimeter region [0.1-20 terahertz (THz)] are emerging technologies in the field of optics research. Thanks to recent advances in related science and technology [l]-[6], it has been proposed that THz technology be applied in many fields such as early diagnosis of cancer, detection of counterfeit bills, and moisture analysis.

The features of lightning shielding of transmission lines have been calculated using the electrogeometric model (EGM) proposed by Armstrong and Whitehead. Discrepancies, however, have been found in the case of ultra-high voltage (UHV)-designed transmission lines. UHV-designed transmission lines often pass through high-altitude mountain areas, where foggy or rainy conditions are common when there is lightning. While the electrogeometric model determines the striking distance based on the lightning stroke current, environmental conditions, and how they might affect lightning discharge paths, they are not considered. It is possible, therefore, that foggy conditions may cause differences in the performance of transmission-line lightning shielding. This study used scale models of transmission lines for discharge tests with a 1-m air gap and analyzed differences in discharge paths and locations in dry and foggy conditions. The results showed that the polarity of the discharge had a significant influence, but differences in dry and foggy tests were negligible.

The electric geometry model suggested by Armstrong and Whitehead was used to calculate the performance of lightning-shielded transmission lines. However, since the ultra high voltage (UHV) designed transmission lines were brought into 500 kV operation, it has become evident that their actual performance is different from the calculated predictions in terms of their actual faults, lightning observation results, etc. It is thought that the UHV designed transmission lines are subjected to foggy or rainy conditions when lightning strikes, because they often pass through mountainous areas at higher altitudes. However, according to the electric geometry model, the striking distance is determined by the lightning-stroke current value only, and the model does not consider the environment of discharge path for the relevant lightning strokes. These considerations suggest that foggy conditions may affect transmission line lightning shielding performance. In this study, discharge tests were conducted using a scaled-down transmission line with a 5 m air gap. The discharge point to the simulated conductor was analyzed in both dry and foggy conditions. Tests were also conducted with a DC bias applied to the simulated power lines, to take the operating voltage of the lines into consideration. These experiments have shown that the effect of fog on the discharge ratio to the conductors is negligible.

Development of decision support tools for maintenance strategy of electric power equipment based on the asset management technique becomes very intensive in order to reduce maintenance cost due to the liberalization of power business. In these years many theses have been presented about asset management in this area, but there are not yet so many concrete researches. This article introduces two approaches of decision support tool development for power equipment in CRIEPI. One is to support evaluation of dissolved gas analysis for oil-immersed transformers. It provides comparison to data obtained from the same kind of transformers, and criteria among them. The other is to evaluate average annual maintenance cost by considering an overhaul effect and failure risk. It provides an optimum overhaul strategy with suitable parameters.

From the viewpoint of reducing the cost of electric transport, a pole transformer has been operated, for a trial, under a short-time overloaded condition. It is not clear how long it takes a pole transformer to deteriorate under an overloaded condition, therefore, a pole transformer lifetime evaluation method is necessary. To realize this method, we developed a transient temperature calculation method from the load pattern and temperature of the outer section of the temperature, and evaluated its accuracy by comparing measurement results and calculations. We developed an estimation method of the degree of polymerization of insulating paper at varying temperature from the measurement result at various temperatures and times in the pole transformer atmosphere.

Electromagnetic waves are named depending on their wavelength range. For many years, the generation methods, detection methods and applications of almost all electromagnetic waves have been investigated. However, there remains an unveiled range owing to a lack of appropriate generation methods. This wavelength range is from several tens to several hundreds of micrometers, and has a frequency range from one to several tens of THz. Generally, waves in this range are called the THz waves. Some generation methods for THz waves have been developed recently, the characteristics of these waves are still under investigation, but some applications have been proposed. One of the important properties of THz waves is their high transmissivity in opaque dielectric materials. Generally, insulating materials are opaque to visible light, and it is difficult to observe internal defects externally. However, if THz waves show sufficient transmissivity and proper interaction with internal physical quantities, they are expected to be a useful measurement tool for insulating materials. In this study, polyethylene, which is a typical insulating material, is choosen as the measurement target, and void interfaces and mechanical strain are detected using THz waves.

As mechanical vibration usually exists in HV motors and generators, its influence on the partial discharge (PD) needs to be studied so as to improve the reliability of on-line PD monitoring method. In this report, the mechanical vibration frequency was synchronized to the power frequency and the effects of vibration phase and frequency were investigated. Because the length of the discharge gap changed with the vibration, obvious variation in the slot-PD patterns was observed at different vibration lead phase and frequency. Moreover, when the vibration amplitude was large, it was also found that the PD behavior at low voltage just above the PD inception voltage was different from that at higher voltage. This was explained in terms of the effects of the field variation in the gap due to the vibration and the charges left on the insulating surface due to PD.

Partial discharge (PD) inception characteristics of liquid nitrogen (LN_2)/ polypropylene (PP) laminated paper composite insulation system for high temparature superconducting (HTS) cables were investigated in terms of the volume effect and the V-t characteristics. The electrical and optional measurements of PD inception characteristics showed that initial PD could be generated between PP laminated paper layers, as well as in a butt gap. Using a parameter called satistically stressed liquid volume (SSLV) based on the discharge probability in both butt gaps and LN_2 filled thin layers between PP laminated papers, we could systematically analyze and evaluate the volume effect on PD inception stress (PDIE). Furthermore, experimental results revealed that n values of V-t characteristics at PD inception were as high as 80-110. On the other hand, the lower n values obtained at breakdown were interpreted by the intensified PD development in thermal bubbles generated after the PD inception.

The allowable current of an underground power cable system is evaluated on the basis of the temperature rise of a conductor. Generally, the steady allowable current is evaluated on the basis of saturated temperature rise. Because there is a large difference between the time constant of heat conduction in a cable and that in soil, loss factor (Lf) is generally used. However, when an allowable current is calculated using Lf, there is a possibility of overestimation, such as in a shallow laying case. We previously developed programs for evaluating the transient temperature rise of power cables in a protection pipe with actual transient load change. Using these programs, we can evaluate the overestimation due to Lf in this study. Among the cases we assumed to be normal, there occurred 5°C of overheating of a protection pipe and 3°C of overheating of a conductor.

Although surface discharges are one of the principal kinds of phenomena associated with faults in electrical apparatus, they have not yet been fully elucidated. Electric field measurements in and around a corona streamer during the creeping advance of a surface discharge are very helpful in analyzing discharges. Pockels crystals have been used in the optical measurement of electric fields, and an optical waveguide technique has been successfully used to miniaturize the sensors. Electric field measurements are made just beneath a surface discharge with an optical waveguide Pockels sensor installed on a PMMA plate and output signals expressing the development of the discharge are obtained. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 28–34, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10185

Most of the aged high-voltage (HV) power capacitors are the oil-immersed paper capacitors in Japan. Hence, it is necessary to establish an on-site partial-discharge (PD) diagnosis of the oil-immersed paper capacitors. The capacitance of the capacitors is very large, so it is difficult to apply HVAC to the capacitors. Therefore, it is difficult to perform the PD measurements of the capacitors. These difficulties may be overcome by an oscillating-wave test system (OWTS) that has the compatibility between high output and compactness. In this paper, to investigate the applicability of OWTS to PD diagnosis of the capacitors, PD measurements of the aged capacitor were attempted by OWTS. Furthermore, the various countermeasures against high charging current of capacitors in PD tests by high-frequency current transformer (HFCT) were investigated.

The present paper describes two kinds of techniques aiming at improving THz imaging for detecting rust under coated steel plates. First, it is revealed that a THz camera considerably shortens the THz-imaging time, but fringe patterns due to high coherence light source sometimes prevent image concatenation. Second, a program flowchart to quantitatively estimate the degradation level of rust is also presented.

In 2011, Japan suffered from a massive earthquake and tsunami. Thermal power plants operated by the Tohoku Electric Power Company were also affected by seawater inundation. Almost all power equipment such as switchgears, motors, cables, wires in Shin-Sendai Thermal Power Plant were inundated. This study investigates seawater intrusion in several low voltage wires, and discusses the refurbishing criteria required to realize rapid restoration of the plant. Nearly 2600 wires were subsequently reused, and recovery was completed within five months. The plant resumed its commercial operation at the end of 2011, and wires have been working well until now.

Electric utilities have tried to improve their quality of services. At the same time, total expenses should be reduced as much as possible. In this paper, a method to analyze economical operation period of transformers is proposed to solve the problems. There are two approaches performed in this paper, analysis using transformer failure statistics and analysis using transformer operational data. Analysis using transformer failure statistics and population data is carried out as general economical operation period characteristic of the transformers that operate at PLN Java Bali Transmission and Load Dispatch Center. Another analysis using transformer operational data is carried out to give specific economical operation period characteristic of transformer. Four operating conditions with different load and water content are studied to determine economical operation period of transformers for each condition.

Degree of polymerization (DP) is thought to be a good index to determined deterioration level of insulation paper in power transformers. In practical conditon, using this method is complicated and expensive due to the necessity of disasembling the transformer. Therefore an alternative method has been expected. In this paper a new method to estimate DP from load and temperature histories is proposed. The exsistence of moisture also considered. Mechanical strength of insulation paper of power transformers in Java Bali Region is assesed using the estimated DP based on the real load and temperature data. Furthermore failure probability of those transformers is considered based on the design stresses in a transformer winding generated by fault currents. Finally the estimated DP values are compared with those from furfural test.

To establish maintenance strategies to reduce costs is one of the crucial issues of electric power industry. So asset management support tools are expected to be developed. The authors have developed support tools for asset management of several kinds of electric power equipment, such as transformers, gas-insulated switchgears, overhead transmission lines. In this report, some of the tools are explained and some important points to develop those tools based on the authors experiences during development processes of those tools. Those tools are aimed to give the minimum maintenance cost over target time interval such as 30 years based on the maintenance cost data. The authors also develop an evaluation model for typical maintenance methods, CM (corrective maintenance), TBM (time based maintenance) and CBM (condition based maintenance) which utilizes several input information, such as equipment age distribution, life time probability density distribution and accuracy of life time diagnosis. This model can evaluates annual and average maintenance cost during operation period of equipment, and these maintenance methods are compared each other.

Making good balance between power demand growth-and power equipment installation is one of important issues of electric power companies. Appropriate strategies of managing existing power equipment and reinforcement are necessary for obtaining the maximum quality of electricity supply with the optimum energy cost. Strategies for the existing equipment include maintenance and replacement planning. In this article, a method to evaluate average annual cost for maintaining a transformer is introduced based on real failure data of transformers. Using the method, an economical service period of transformers can be eventually estimated. Cost analysis includes transformer's initial cost, maintenance cost, and cost in the event of failure. Analysis is performed using statistical data from PT. PLN Indonesia.

The applicability of terahertz (THz) waves to the detection of rust in coated steel plates has been examined. Spectral intensity measurements of reflected light from a sample coated with epoxy resin show that optical coherence tomography using near-infrared light and THz waves can detect the hidden rest region. This region can be reproduced by so-called THz imaging without contact. Since rust exhibits strong absorption in the frequency range from 1 to 5 THz, the absorption coefficient can be used to estimate the rust state with high sensitivity. In contrast, neither X-ray fluorescence nor Fourier transform infrared spectroscopy can detect the rust, because of the strong X-ray and IR peaks of the coating. Electro-chemical impedance measurement, which is one of the promising diagnostic methods, judges the water blocking ability of the coating. The impedance value and THz absorption due to rust shows good correlation until the amount of water in the film reaches its maximum.

One of the recent topics of optical measurement techniques is the generation and utilization of the “Terahertz wave (THz wave)”. In the long history of the research on electromagnetic waves, it remains as the last unrevealed area because its generation and detection techniques have not been sufficiently developed. In recent years, some useful and convenient devices have become commercially available, and much related research is being carried out. One important feature of THz wave is the high transmission probability through some opaque materials, many of which are dielectric materials through which a visible light beam cannot pass. Solid insulating materials are usually opaque dielectric materials, and it is difficult to measure their interior by conventional optical measurement techniques. If THz wave can pass through an insulating material sufficiently, the same measurement technique as with a visible light beam, already developed and practically applied, such as the technique of utilizing polarization, will become applicable. In this chapter, the research work on the introduction of THz wave techniques to the internal measurement of solid insulating materials is reviewed [1,2].

The authors have confirmed that most major cause of degradation for 6 to 60 kV class XLPE cable in Japan is water trees with needle shape, which would develop only a few in an XLPE cable with its length of 100 m or so. Therefore, establishment of the detection and diagnostic methods for such water trees is important for degradation assessment and lifetime prediction of aged XLPE cables. The authors have focused on the application of damped ac high voltage (DAC) combined with partial discharge measurement for the water tree diagnosis. This paper deals with the influence of repetitive application of DAC on the insulation performance of water tree aged XLPE cable in order to confirm harmlessness of DAC application from viewpoint of partial discharge characteristics.

6 to 60 kV class XLPE cables are widely used and playing important roles in power distribution and transmission systems in Japan. The aging degradation is dominated by water trees in these XLPE cables. Therefore, water tree diagnosis with high precision is quite important for operation, maintenance and replaces planning of these XLPE cables. The authors have been investigating the applicability of the Damping oscillating high voltage (DOHV) to the water tree detection as well as insulation diagnosis for these XLPE cables. This paper firstly proposes the nondestructive insulation diagnosis using DOHV application. Then, some empirical results obtained by its application to water-tree degraded XLPE cable are discussed.

Many plant infrastructures in Japan were set up in the high-growth period (from the 1960’s to the 1980’s), and electric equipments installed with them have become old. Some maintenance is being made in order to extend their life, but the effects are limited and renewal should be planned. Generally, investment in equipment is concentrated on a high productivity area. The renewal of old equipments doesn’t make large profit, and the distribution ratio of investment tends to be small. It is very important subject to utilize the limited investment effectively for maintenance and renewal. For this theme, there is a great deal of interest in asset management techniques that incorporate economic indicators and trouble risk evaluation for service-aged equipments. “Plant Asset Management” is expected for not only maintenance cost cutting but also stable and effective plant operation.

Two types of resin-coated papers were investigated; kraft papers and heat-resistant kraft papers partially covered with epoxy resin; those were laminated to some thickness. They were thermally degraded at 120degC for 240 to 1320 hours, and their mechanical strength, i.e. tensile strength was measured. The tensile strength of the resin-coated kraft paper decreased with the heating time and became smaller than that of the pressboard after 500 hours while the tensile strength of the resin-coated heat-resistant kraft paper almost retained the initial value after 1320 hours of the heating time. Then, electrical breakdown characteristics of composite insulation systems with a resin-coated paper and insulation oil were investigated. In the system, an oil-filled gap was artificially introduced between the resin-coated paper and a plane electrode to induce partial discharge (PD) initiation at the same location. PDs occurred before breakdowns and their PD inception electric field strength was almost as high as pressboards and the effect of the heating time was negligible. Characteristics of electrical breakdown field strength were similar to the PD inception field strength; negligible effects of the type of the resin-coated papers and the heating time. Electrical breakdown occurred at the oil-filled gap and the edge of a high voltage electrode.

In this paper, only very small parts of research topics in CRIEPI are introduced. CRIEPI welcomes all the researchers who are interested in the field mentioned in this paper, to have variable discussion for the technologies and investigations mentioned above.

6 kV to 60 kV class XLPE cables are widely used and have been playing important roles in power distribution and transmission systems in Japan. For the XLPE cables in these voltage levels, the water tree dominates aging degradation. Therefore, precise on-site detection techniques of water trees in their length are considered to be important for operation and maintenance of these XLPE cables. The author has been investigating the applicability of the dumping oscillating high voltage (DOHV) to the water tree detection as well as insulation diagnosis for these XLPE cables. This paper firstly investigates on the partial discharge measurement under DOHV application for water tree deteriorated 6.6 kV XLPE cable. Then, authors discuss the applicability of OHWV to the insulation diagnosis of XLPE cables combined with partial discharge measurement under DOHV application.

We discussed partial discharge (PD) inception characteristics of liquid nitrogen (LN/sub 2/)/polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables. In this paper, we measured PD inception characteristics under lightning impulse voltage application by both electrical and optical methods. The impulse PD inception characteristics were compared with those under ac voltage application, and the PD generation mechanisms were discussed. Experimental results revealed that PD detection sensitivity under lightning impulse voltage application reached as small as 6 pC. PD was verified to be generated not only inside the butt gap but also outside the butt gap under both lightning impulse and ac voltage applications. AE sensors could also be applied to PD measurement under ac voltage application.

With the aim of developing XLPE insulation for extra high voltage cable, we investigated the morphology of cross-linked polyethylene. We used a kind of base materials and additives, and controlled curing condition and amount of additives. The effect of addition of additives on morphology of XLPE such as lamellar density, orientation and additive layer were analyzed using TEM analysis and X-ray diffraction test. For evaluation of breakdown strength of XLPE insulation with additives and base materials, the mold-type XLPE specimens were made and evaluated with Weibull plot parameters, and compared with morphological characteristics. We applied this result to model cable and this model cable was found to have superior dielectric strength and morphological characteristics compared with non additive added model cable.

As mechanical vibration usually exists in HV motors and generators, its influence on the partial discharge (PD) needs to be studied so as to improve the reliability of on-line PD monitoring method. In this report, the mechanical vibration frequency was synchronized to the power frequency and the effects of vibration phase were investigated. Because the length of the discharge gap changed with the vibration, obvious variation in the slot-PD patterns was observed at different vibration phase. Moreover, when the vibration amplitude was large, it was also found that the PD behavior at low voltage just above the PD inception voltage was different from that at higher voltage. This was explained in terms of the effects of the field variation in the gap due to the vibration and the charges left on the insulating surface due to PD.

In this paper, we discussed partial discharge (PD) inception characteristics in liquid nitrogen (LN/sub 2/)/polypropylene (PP) laminated paper composite insulation system in terms of volume effect and V-t characteristics, both for PD inception strength (PDIE). Different kinds of butt gap condition were applied in the experiments, using parallel plane and coaxial cylindrical cable samples. Experimental results revealed that the volume effect on PDIE could be evaluated by the statistical stressed liquid volume (SSLV) taking account the discharge probability not only in the butt gap but also in the other thin layers between PP laminated papers. Furthermore, the indices n of V-t characteristics at PD inception were estimated to be 80/spl sim/100, irrespective of the butt gap condition.

This paper introduces concepts of the all solid insulated substation, which features environmental benignity, compactness, reduction of construction cost, being free from maintenance work, and so on. In the actualization of the all solid insulated substation, many problems have to be conquered, such as the development of the solid insulating materials with high heat conductivity and reasonable electrical insulating performance for a solid insulated transformer, a solid insulated compact connection system between power equipment, nondestructive diagnostic technique for the solid insulating materials, semiconductor switching devices for mechanics less power equipment, etc. This paper also depicts some part of our investigation.

In order to reduce construction cost of substations and to become more environmentally benign, we have been proposing the All Solid Insulated Substation as a next generation substation, in which the high voltage section like busbars and transformer windings are insulated by the solid insulating materials such as epoxy resin and silicone rubber. In the All Solid Insulated Substation, compact connection systems between each piece of power equipment have to be developed for the reduction of the volume and area of the substation. From these viewpoints, this paper introduces the concept of the All Solid Insulated Substation and describes basic experimental investigation for the development of the compact connection system.

Though many studies on life extension of power apparatus have been carried out recently, it is inevitable to replace them in the not too distant future. However, if replacements of apparatus occur simultaneously, manufacturers may not able to supply the apparatus within a reasonable cost. This letter proposes a rational replacement scheme to avoid such supply risk. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.