This article deals with trend of sensing, monitoring, diagnostics and maintenance technology in electric power apparatus, especially, gas insulated switchgear (GIS). Partial discharge measurement is one of key technology and the most promising method for developing highly reliable diagnostics for insulation performance of the high voltage apparatus. The review is made by focusing UHF sensors and acoustic method for detecting electromagnetic and ultrasonic waves caused by partial discharges in GIS, respectively.

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We constructed a leakage current measuring system which can separate it into three frequency components in frequency domain, low (0_??_360 Hz), middle (360 Hz_??_5 kHz), and high (10MHz) frequency. The low, middle and high frequency components are intended to correspond to surface leakage current, dry-band arc and corona discharge, respectively. We verified the developed system so as to confirm that the leakage current mainly containing dry-band arc component has frequency spectrums dominating near several kHz. This new separative leakage current measuring system was applied to the salt-fog test using porcelain samples as a reference. Consequently, we found that the proposed separative measurement is effective to discuss quantitatively the degradation properties of polymer materials as well in the accelerated degradation evaluation test.

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A fault diagnosis system has been developed to prevent serious accidents in a hydraulic turbine generator by detecting anomalies in their early stages. The system predicts the bearing temperature change by using the physical dynamic model of the bearing related components, such as the bearing pad and lubricating oil cooler. The unmeasurable parameter values in the model, e.g. bearing gap width, are estimated on-line by minimizing the differences between the measured and calculated values of bearing and oil temperatures using a nonlinear optimization method. The system detects and diagnoses the anomalies based on the prediction results and estimated parameter values.After evaluating the feasibility using a 1/3 scale test facility, the system was installed in the Okutataragi Pumped Storage Power Plant of the Kansai Electric Power Co., Inc. Accurate prediction performance was confirmed for the system which is now being used for commercial operation.

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At substations or sectioning posts of Shinkansen, a pair of single-phase power sources are provided in different phase. When a Shinkansen car passes the boundary between the two power sources, the changeover section (about 1km long) with a pair of vacuum changeover switches the power sources for the car instantly.
There were no ways to detect the flashover of vacuum switch used as a changeover switch before, so we wasted a long time sometimes to specify the fault reason.
We analyzed the fault current carefully, to find the facts:
When the changeover switches are normal, a current flows through only one switch.
When the fault occurs on a changeover switch with no cars in the changeover section, fault current flows through both switches to make the currents in the two switches the same.
When a fault occurs on a changeover switch with a car in the changeover section, both fault current and load current flow. In this situation the currents in the two switches are different.
Then we have developed a new type protective relay for Shinkansen changeover switches based upon the facts. This relay has a pair of over current detectors with a pair of optical current transformers to detect the current in each changeover switch. When it detects the over current of both switches, it can judge that a flashover has occurred in one of the changeover switches.

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A thermal image has been often used to inspect a power apparatus. If an automatic diagnosis method for the apparatuses by thermal images is developed, it makes inspection more efficiently. Then, a new method of diagnosis of a power distribution apparatus by a thermal image is developed as one of functions incorporated into a monitoring device that moves on a ground wire. The method consists of both extraction of an apparatus from a thermal image by using installation pattern of apparatuses and detection ofa faulty apparatus by local temperature gradient. The experiments with the proposed method were done under many different conditions like different weather, time, and season. An error rate of 3%is obtained with the experiments of extraction of an apparatus. And an error rate of 17% is obtained with the experiments of detection ofa malfunctioning apparatus. The proposed method could extract and detect them except the case that the distance between a pole and an infrared camera was so far that the intensity sensitivity was not sufficient.

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To check and protect the water-wheel generators with a much faster and simpler method during the operation, an insulation diagnostic method using an AE (Acoustic Emission) sensor has been proposed. The insulation diagnostic technique needs to separate the AE signal generated by the partial discharge from the AE signal including the machine noise. Therefore, the AE signal during the normal operation was compared to the AE signal when the rotor revolved at the non-excitation condition. Moreover, we measured the AE signal while the generator was operated normally for a long time. The AE signal were analyzed using the FFT and Wavelet processing techniques. As a result, the AE signal could be separated in to the machine noise level and the AE signal level produced by the partial discharge, and the temperature of stator winding was related to the partial discharge from the measured AE signal.

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This paper describes a new method of measuring partial discharge (PD) via coaxial bonding wire for direct-buried power cable, with which partial discharge can be measured at the so-called link box usually installed beside the joint but on the ground. When cable joints are directly buried under ground, it is difficult to use the conventional measuring method to detect PD, since it is necessary to install a PD detection sensor directly at or on the joint. For direct-buried cable line, the formation of sheath bonding for each joint can be usually determined at a link box that is connected to joint via coaxial bonding wire. Five kinds of PD sensing circuits were proposed for PD measurement at link box and the methods have been verified through several experiments using sample cables in laboratory or being carried practically on a real cable line on-site. The paper summarizes the experimental results and gives a comparison of each method. The paper also shows the possibility of measuring PD for three phases instantaneously at one joint bay on-site. Some practical PD measurement for those kinds of direct-buried power cable conducted onsite will be also introduced with on-site photos.

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Recently, power systems have become larger and more complicated, and the rate of constant power load has increased. Under the situation like this, concerns about voltage instability phenomena have been raised. Therefore, in addition to the conventional local voltage control, the necessity of global on-line voltage control scheme has risen.
In this paper, we propose a method of on-line voltage stability control including preventive and emergency-preventive controls to retain voltage stability even if a severe fault occurs. According to the result of contingency analysis for severe faults, we consider operation of control equipment as preventive control. And in case that the fault seems still severe after preventive control, we consider load curtailment as emergency-preventive control. When we select the control equipment and loads to curtail, we use voltage stability index VIPI sensitivity. And we determine the amount of control and load curtailment using Optimal Power Flow calculation. The effectiveness of the proposed method is verified by simulations using a 28-bus system.

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As for harmonic, which is one of the electric power qualities, it becomes important to obtain harmonic voltage/current distribution of the power system precisely because the use of power electronic apparatus is increasing widely. However, there are some difficulties on evaluating the measured data in comparison with the simulated results; i.e. measurement errors of the harmonic voltage/current, difficulty of the synchronized measurement at several substations and so on. In order to evaluate power system harmonics precisely, we applied the harmonic state estimation method to power system of our company and verified the method.This paper describes the research that precision grasps of the harmonic distribution in power system by using the multi-function measuring system via GPS and harmonic state estimation method.

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For improving electric power system transient stability, synchronous generators in power systems are generally equipped with the controllers such as AVR, PSS, and GOV. Since the various oscillation modes occur according to system conditions, however, these fixed parameter controllers deteriorate the control performance.
We propose adaptive power system stabilizer(PSS) using frequency domain analysis for improving electric power system transient stability for multi-machine power systems. In the proposed method, at first, the frequency components of the generator's swing are detected by real time FFT. The conventional PSS parameters are tuned online by a fuzzy controller based on the obtained frequency domain analysis. We verify that the proposed adaptive PSS using frequency domain analysis can damp the generator's swings effectively.

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The rechargeable batteries like Redox Flow which aren't aged by frequent charging/discharging, have a quick response equivalent to SMES and outstanding capability of overload. The response time and the maximum overload rate of Redox Flow battery are verified as 350μs and 4.6 times. The battery efficiency increases when the cycle period of charging/discharging becomes shorter. The battery is advantageous for secondary control in the power system and maintenance of power quality as distributed power resource in addition to leveling load. The instantaneous controls using these systems are also effective for dynamic stability, flicker, voltage dip and charging/discharging regenerative power of electric railways. The authors clarify the chemical reactive characteristics of Redox Flow battery physically and make the Redox Flow Battery Model which can be used for impact study for maintaining power quality and calculation of operational cost. The comprehension about these performances can be used to determine the optimum rechargeable battery system for each end use.

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EIE-core type variable inductor is the equipment of variable inductance, which is controlled by dc current. This device controls the cancellation effect of AC magnetic flux. Accordingly, the device always keeps the flux density on the magnetic path within a saturation flux density on control-mode. And, the device cancels a high harmonic distortion, does not need the gaps, which reduce a distortion. Therefore, the device is simply structured, and is easily to scale up.
This paper describes a basic structure, basic characteristics (exciting, distortion, ...etc.), and examples of application for the electric power equipment.

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The MHD flow behavior and the performance of an experimental nonequilibrium subsonic disk MHD generator driven by a shock-tube facility have been examined with time-dependent r-z two-dimensional and r-θ-z three-dimensional Large Eddy Simulation for the first time. The calculation region is extended and covers a hot duct through a downstream duct including the subsonic MHD generator with two throats. For optimal and high load operations, the flow chokes at the downstream throat and the subsonic flow is maintained in the generator channel. The discharge structure is uniform in the θ direction, and the suitable fluid flow is realized in the generator channel, although the large boundary layer separations and eddies are observed behind the downstream throat. For low load operations, the flow chokes at the upstream throat and the flow becomes supersonic, where pseudo-shock waves and large eddies are observed in the generator channel and the downstream duct. The ionization instability in the r-θ plane occurs in the generator channel, which deteriorates the generator performance. Asymmetric flow at the generator inlet, which is attributed to the change of flow direction from the hot duct, seems not to be significant for the generator performance.

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A drawback of direct methanol fuel cell (DMFC) is too much permeation of methanol through a polymer electrolyte membrane (PEM), which reduces fuel efficiency and the cell performance. We have been studied direct di-methyl-ether (DME) fuel cell instead of DMFC for some years ahead. This paper reports the permeation properties of DME through a PEM as compared with that of methanol through a PEM.
The permeability coefficient of DME through a PEM was about one-tenth as small as that of methanol through a PEM. It decreased extremely with decrease of humidity, whereas the permeability coefficient of methanol changed little with decrease of humidity. Effects of temperature on the permeability coefficient of both DME and methanol were relatively small. Nafion^® 112, Nafion^® 115, Nafion^® 117 and Aciplex^® s-1002 were tested as the PEMs. Asiplex^® s-1002 showed lower permeability coefficient than Nafion^® of the same thickness. When aqueous methanol was fed instead of gaseous methanol the permeability coefficient of methanol through a membrane increased with increase of temperature. The difference of methanol permeation properties between gas feed and liquid feed can be explained by the gas-liquid equilibrium of aqueous methanol.
Direct DME fuel cell is attractive from a view point of low fuel permeation through a PEM.

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Abstract: The concept of “frequency response of damping torque coefficient” as a performance index of power system damping controller is discussed. It is pointed out that the concept does not have sound theoretical basis. The frequency response may be an approximation to damping torque coefficient only on representative oscillatory frequency. All other points on the frequency response curve, however, don't have any meaningful information on damping of oscillation.

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