Vacuum Circuit Breakers (VCBs) have been widely used for medium voltage level, because of their performance: compact size, light weight, maintenance free operations and environment-friendly characteristics. They become most comfortable breakers for our needs from other breakers: oil, air, magnetic blast and gas. In this paper the history of vacuum, and latest trends of circuit breakers and related technologies are described, as well as merits or demerits of using vacuum technologies.

View full abstract

The geothermal power generating facilities that utilize the geothermal energy from the earth are environment-friendly, because they scarcely emit the greenhouse gases such as carbon dioxide (CO₂) or the environmental pollution substances such as nitrogen oxides (NOx) and sulfur oxides (SOx). On the other hand, they should work swallowing the geothermal steam that contains much amount of chemical impurities such as hydrogen sulfides (H₂S), sulfates (SO₄^2-), chlorides (Cl^-), silica (SiO₂), etc. Therefore, it is not too much to say that the geothermal power generation is a fight against the chemical impurities. Since the first practical geothermal power generating facility in Japan began operating with a small capacity of 30kW in 1960 at Hakone Kowakien, Japanese manufacturers have been developing geothermal power generating facilities and supplying them worldwide. The geothermal power generation is one of the technical challenges that gives a hope for a sustainable development of the human society.

View full abstract

SF₆ gas is applied widely to medium voltage switchgear because of its high insulation reliability and down-sizing ability. However, SF₆ gas was placed on the list of greenhouse gases under the Kyoto Protocol in 1997. Since then, the investigation and development concerning SF₆-free or less has carried out activity. Therefore, we paid attention to the solid material which has higher dielectric strength than SF₆, and we have newly developed solid insulated switchgear (SIS) achieved by molding all main circuit. A new epoxy casting material is applied, which contains a great deal of spherical silica and a small amount of rubber particles. This new material has the high mechanical strength, high thermal resistance, high toughness, and also high dielectric strength because of directly molding the vacuum bottle, down-sizing and reliability.
This paper describes about the technology of a new epoxy casting material which achieves the SIS. In addition, the mechanical and electrical reliability test of SIS applied a new epoxy resin are carried out, and effectiveness of the development material and the mechanical and electrical reliability of SIS are verified.

View full abstract

A new 72kV rated low pressured dry air insulated switchgear applying electromagnetic actuation and function that supports CBM has been developed. First, dielectric characteristics in dry air under lightning impulse application has been investigated at bare and insulator covered electrodes. Dependence of the breakdown electric field strength on the effective area has been clarified to apply the configuration design of the insulation mold for the vacuum interrupter. In addition, moisture volume dependence on surface resistance has been clarified to decide moisture volume in gas pressure tank. Next, a new vacuum circuit breaker (VCB) has been designed. To keep dimensions from former 72kV SF₆ gas insulated switchgear, distance between contacts in vacuum interrupter is needed to be shorter than that of former switchgear. Voltage withstand capability between electrodes practically designed for vacuum interrupter has been investigated under dc voltage application simulated the small capacitive current breaking test. Gap configuration including contacts and slits has been optimized and distance has been shortened 11% from former switchgear.
As a result, the new low pressured dry air insulated switchgear has been designed comparably in outer size to former SF₆ gas insulated switchgear. Using dry air as an insulation medium with low pressure has been able to reduce the environmental burden.

View full abstract

Electrode conditioning is very important technique for improvement of the insulation performance of vacuum circuit breakers (VCBs). This paper discusses the spark conditioning mechanism under non-uniform electric field focused on the pre-breakdown current. We quantitatively evaluated the spark conditioning effect by analyzing the pre-breakdown current based on Fowler-Nordheim equation. As a result, field enhancement factor β decreased with the increasing in breakdown voltage in the beginning of conditioning process, and finally β was saturated with the saturation of breakdown voltage. In addition, in case of non-uniform field, we found that β on high voltage rod electrode after conditioning varied according to the electric field strength on the rod electrode.

View full abstract

To investigate the reliability of equipment of vacuum insulation, a study was carried out to clarify breakdown probability distributions in vacuum gap. Further, a double-break vacuum circuit breaker was investigated for breakdown probability distribution. The test results show that the breakdown probability distribution of the vacuum gap can be represented by a Weibull distribution using a location parameter, which shows the voltage that permits a zero breakdown probability. The location parameter obtained from Weibull plot depends on electrode area. The shape parameter obtained from Weibull plot of vacuum gap was 10∼14, and is constant irrespective non-uniform field factor. The breakdown probability distribution after no-load switching can be represented by Weibull distribution using a location parameter. The shape parameter after no-load switching was 6∼8.5, and is constant, irrespective of gap length. This indicates that the scatter of breakdown voltage was increased by no-load switching. If the vacuum circuit breaker uses a double break, breakdown probability at low voltage becomes lower than single-break probability. Although potential distribution is a concern in the double-break vacuum cuicuit breaker, its insulation reliability is better than that of the single-break vacuum interrupter even if the bias of the vacuum interrupter's sharing voltage is taken into account.

View full abstract

A new electromagnetically actuated vacuum circuit breaker (VCB) has been developed for a 72kV rated switchgear. Each phase of this VCB has a plurality of compact electromagnetic actuators linked mechanically providing the required driving energy. The mechanical linkage working as a lever magnifies an actuator stroke to the required stroke of a 72kV rated vacuum interrupter. An electromagnetic analysis coupled with motion, which considers the mechanical linkage of the plural actuators, has been developed for designing the driving behavior of this VCB. Using this analytical method and a quality engineering method known as the Taguchi method, we have clarified effective parameters to reduce the time difference of the driving behavior for tolerance specifications. Moreover, analyzing the oscillatory behavior closing the contacts, a structure of this VCB has been designed to reduce the bounce duration. The developed new VCB has been confirmed that a time difference is short enough and bounce duration is reduced. This VCB is highly reliable against variations in manufacturing and environment.

View full abstract

Switching surges are of primary importance in insulation co-ordination of EHV and UHV networks, as well as in designing insulation of apparatuses. The magnitude and shape of the switching overvoltages vary with the system parameters, network configuration and the point-on-wave where the switching operation takes place. Although some studeis were carried out for design of the networks, but power systems are gradually developed and their configuration is changed. It is important for the utilities to ensure that the peak overvoltage and global risk of the network resulting from the switching operations are well within safe limits. Optimization problems of power networks are very difficult to solve because the power networks are complex and widely distributed. This paper presents a simulation optimization approach in order to find the peak value of switching overvoltages and optimum location of arresters, as protective device, in EHV and UHV networks. In the proposed method, the Artificial Neural Network (ANN) as meta model estimates the peak value of overvoltages and global risk of failure generated by switching transients. An optimization method based on genetic algorithm (GA) determines the best positions of surge arresters on power networks so as to minimize the global risk of the network.

View full abstract

The influence of voltage sag to electric equipment has become big issues because of wider utilization of voltage sensitive devices. In order to reduce the influence of voltage sag appearing at each customer side, it is necessary to recognize the level of receiving voltage drop due to lightning faults for transmission line. However it is hard to measure directly those sag level at every load node.
In this report, a new method of efficiently estimating system voltage sag profile is proposed based on symmetrical coordinate. In the proposed method, limited recorded sag data is used as the estimation condition which is recorded at each substation in power systems. From the point of view that the number of the recorded node is generally far less than those of the transmission route, a fast solution method is developed to calculate only recorder faulted voltage by applying reciprocity theorem for Y matrix. Furthermore, effective screening process is incorporated, in which the limited candidate of faulted transmission line can be chosen.
Demonstrative results are presented using the IEEJ East10 standard system and actual 1700 bus system. The results show that estimation accuracy is sufficiently acceptable under less computation labor.

View full abstract

The number of damages of home electric appliances due to lightning surges have recently increased. Instllation of SPDs (Surge Protective Device) in interior wireing is one of countermeasures against the damages and is also spreading after an amendment of the regulation on indoor wires in 2005. Past study showed effective mthod, the earth line of SPD is connected with that of home appliances and is grounded at one place at home.
However, because the institution ways of the distribution line at each home are various, it is difficult to estimate the effect of SPD at every home, and the high-precision analysis by EMTP for interior wiring and SPD at home is required. In this study, experiments were conducted with interior wiring and varisters which constitues SPD, and this paper report the results by those experiments and EMTP analytical models.

View full abstract

The authors have developed an innovative FL (Fault Locator) System, which takes the 3-phase unbalance into consideration by simulation of a power transmission line with the distributed constant circuit and use of the theory of mode transformation. The system developed by the authors automatically reads the waveform data of voltage and current from the fault recorder which is time-synchronized to the GPS (Global Positioning System) and measures distance to the fault point using the above-mentioned data and power transmission system data which are set in advance. The authors carried out field tests of the FL System developed by the authors on fourteen lines of the 66kV power transmission system of TEPCO (Tokyo Electric Power Company) and obtained good results that showed a mean error of 0.43[km]. This paper presents these results.

View full abstract

Household cogeneration systems using proton exchange membrane fuel cells (hereinafter abbreviated as PEMFC systems) have attracted attention for their high energy efficiency. To bring out a PEMFC system's performance, it is crucial to use effectively both of electric power and hot water produced from a PEMFC system. Therefore, the optimal scheduling problem of a PEMFC system is very important. However there are difficulties due to the uncertainty of the household energy demand. A difficulty, to which little attention has been paid so far, lies in the difference between the scheduled electric power output and the actual electric power output of a PEMFC system caused by rapid fluctuations of the electric power demand. In this paper, we propose a new method to cope with this problem. In our method, we treat the energy demand as a random variable and calculate its probability density at each time step. Then a constraint that takes into acount the energy demand fluctuations is defined through the probalility density and is cooperated in the original optimal scheduling problem of the PEMFC system. Using our method, we can deal with rapid energy demand fluctuations under the setting of the scheduling problem with long time intervals.

View full abstract

This paper focuses on economic evaluations of a coal-fired thermal power station with a carbon dioxide capture and storage unit (CCS) by which an existing coal-fired thermal power station (COAL) is replaced. Decision makers decide to construct CCS considering both of contrary elements; one is waiting more favorable conditions such as a higher value of carbon credits which CCS has, another is reducing opportunity costs due to delay of construction of CCS. New methods using a real option approach are proposed. Firstly we calculate an economic value of CCS as an American coal option with dividend considering carbon emission costs of COAL as opportunity costs. Secondly we evaluate construction time of CCS using binominal decision tree taking into account the options. Numerical examples show that a real option value of CCS is from 28% to 44% of sales revenue, which are higher than net present values due to a value on waiting for more favorable conditions. And they also show that an earlier construction is exercised and the value becomes lower, the more challenging the benchmark of carbon emissions is or the higher the change rate of maintenance cost of COAL becomes. An effect of a lifetime of power stations is also analyzed.

View full abstract

In recent years, the total capacity of wind power plants connected to power grid has increased drasticaly. However, intermittent output of wind power affect the frequency of the power system. In the night-time the capacity of Load Frequency Control (LFC) tends to be insufficient. On the other hand, Plug-in Hybrid Electric Vehicles (PHEV) are being developed as environment-friendly vehicles. PHEV is a kind of hybrid electric vehicles that can be charged from power grid. The batteries of PHEVs are charged mainly in night-time.
In this paper, the authors proposed the charge control of batteries for PHEVs that compensate the capacity of LFC in the night-time and evaluated the allowable capacity of wind power generations in the penetration scenarios of PHEVs in three areas in Japan. The charge of the batteries was based on driving patterns of passenger vehicles and charging patterns in the night-time that the authors analyzed in this paper. Thereafter, charge control for PHEVs was simulated using transfer fanction models. The authors conducted the simulations and obtained the following results. (1) Charge control for PHEVs can suppress the frequency deviation caused by short period fluctuation of wind power. (2) Charge control for PHEVs including optimal scheduling of charging electric energy with centralized control would suppress the frequency deviation more efficiently than charge control without optimal scheduling.

View full abstract

Using an industrial lithium-ion battery that has higher energy density than conventional valve-regulated lead-acid batteries, a rack-mounted DC-power-supply system was assembled and tested at a base transceiver station (BTS) offering actual services. A nominal output voltage and maximum output current of the system is 53.5V and 20A, respectively. An 80-Ah lithium-ion battery composed of 13 cells connected in series was applied in the system and maintained in a floating charge method. The DC-power-supply system was installed in a 19-inch power rack in the telecommunications equipment box at BTS. The characteristics of the 80Ah lithium-ion battery, specifications of the DC-power-supply system and field-test results were shown in this paper.

View full abstract

As an anti-Vandalism measure, polymer insulator which is light and shows good performance in contamination withstand voltage is already adopted to many new power transmission lines mainly in U.S.A. However, it is said that aging deterioration is promoted by ultraviolet rays, ozone, leakage current and partial discharge because polymer insulator is made of organic materials. It is important that we seize the characteristics of aging deterioration to maintain power transmission lines. As polymer insulator for power transmission lines is more expensive than ceramic one, it is scarely used in Japan, and there is no data in the field.
In this study, we installed polymer insulator to 77kV power transmission line and carried out field test for nine years from 1997 to 2006 and investigated electrical and mechanical characteristics of them.

View full abstract

The overvoltage associated with direct lightning hits has been the important factor for the insulation design of a distribution line. In this paper, the sparkover rate of a medium-voltage line associated with direct lightning hits is investigated based on numerical calculations obtained by using EMTP and statistical analysis by taking account of the correlation between the peak value and the front duration of return-stroke current waveform. When the line is equipped with surge arresters at the interval of 100m in addition to the overhead ground wire, the sparkover rate associated with subsequent strokes is higher than that associated with first strokes. This demonstrates the importance of the study of current parameters for subsequent strokes.

View full abstract

Results of experimental study on performance of the supersonic closed loop with a disk MHD generator are described. The high temperature (> 1900K) argon circulation was carried out successfully during 2.4 hours. The heat gain and loss of argon was investigated, and a large heat loss was found at the diffuser and the exhausting duct although an energy efficiency of recuperator was high. The large heat loss was ascribed to water cooling at the diffuser and the exhausting duct. At the same time, the enhancement of heat transfer coefficient was suggested. The argon temperature and the heat loss calculated under an assumption of four times larger heat transfer coefficient have shown a good agreement with experimental ones. The pressure ratio inside the loop was discussed, and the result has indicated that the total pressure at the upstream of nozzle throat is decided by the total temperature and the mass flow. On the other hand, the total pressure at the downstream is determined by the total mass in the loop and the total pressure at the upstream. The first power generation was carried out, and a good correlation between the load resistance and the Hall voltage was observed. However, the power output remained very small.

View full abstract

The purpose of this research is to verify the validity of the rotation mechanism theory of the SMA engine by experiment. The main results obtained by this research are as follows. We drew up the theoretical formula which predicts rotation speed and output power of the SMA engine. We manufactured the large-sized experiment equipment to measure simultaneously rotation speed and torque, and obtained a maximum output power 3.74W. We compared the experiment values of the rotation speed and the torque with the theoretical values, and partially verified the validity of the theory. We drew up the empiric formula which predicts the maximum output power of the SMA engine.

View full abstract

This paper describes the phenomenon of internal pressure-rise due to arcs that were ignited between the metal rod electrodes in the air. Firstly, the internal pressure-rises in a closed chamber due to arcs were measured with the current within the range of 1 to 12.5kA. The rod electrodes were made of copper, iron and aluminum, and 20mm in diameter. As a measured result, it was clarified that the maximum pressure-rise distinctly differed with each electrode material under the same total arc energy, namely, the maximum pressure-rise was the highest in the case of the aluminum electrode and was the lowest in the case of the iron electrode. Next, to quantitatively verify this difference, the internal pressure was estimated taking into account the energy balance in the closed chamber on each electrode material. As a result, it was clarified that the estimated value of the pressure-rise approximately agreed with the above experimental result by consideration of the oxidation reaction of electrodes, the melting and vaporization of electrodes and radiation loss of arcs under certain realistic assumptions.

View full abstract

Using a high-temperature superconductor, we constructed and tested a model superconducting fault current limiter (SFCL). The superconductor and vacuum interrupter as the commutation switch were connected in parallel using a bypass coil. When the fault current flows in this equipment, the superconductor is quenched and the current is then transferred to the parallel coil due to the voltage drop in the superconductor. This large current in the parallel coil actuates the magnetic repulsion mechanism of the vacuum interrupter and the current in the superconductor is broken. Using this equipment, the current flow time in the superconductor can be easily minimized. On the other hand, the fault current is also easily limited by large reactance of the parallel coil. This system has many merits. So, we introduced to electromagnetic repulsion switch.
There is duty of high speed re-closing after interrupting fault current in the electrical power system. So the SFCL should be recovered to superconducting state before high speed re-closing. But, superconductor generated heat at the time of quench. It takes time to recover superconducting state. Therefore it is a matter of recovery time. In this paper, we studied recovery time of superconductor. Also, we proposed electromagnetic repulsion switch with reclosing system.

View full abstract