The 17^th Power & Energy Society Annual Conference was held on September 13-15, 2006 at University of the Ryukyus. There were 52 technical sessions and 453 papers. A panel discussion, technical exhibitions and technical tours were also organized. In this article, the outline of the conference is reported.

View full abstract

In order to reduce CO₂ emission from residential sector in Japan, PEFC with high efficiency and low environmental impact is expected as one of the promising micro co-generation (μCGS) system. However, the energy demand in houses are largely different each other and the profiles are also changed every day. So, when μCGS is actually introduced, it is necessary to examine the equipment capacity and operation of μCGS in each house respectively. In this paper, the optimization model is developed in order to evaluate the μCGS based on daily-basis demand data. Using actually monitored energy demand data in four households, the differences between using daily-basis data and using the monthly average data are evaluated from viewpoints of economic and environmental performance of μCGS systems. Moreover, by adding the penalty factor to disposal heat of μCGS, the results have been that system configuration and system operation of μCGS can attain CO₂ reduction and energy conservation as well as cost reduction.

View full abstract

In order to grasp properly the power generation performances of PEFC (Polymer Electrolyte Fuel Cell), it is necessary to know the water management data, such as diffusion coefficient of water vapor through MEA (Membrane Electrode Assembly) and GDL (Gas Diffusion Layer), and electro-osmotic coefficient of MEA, and power loss data, such as activation and resistance overpotentials. In this study we have measured these data to analyze our experimental results of PEFC power generation tests by our two-dimensional simulation code. Our code solves simultaneously the mass, charge and energy conservation equations, and the equivalent electric-circuit for PEFC to get numerical distributions of hydrogen/oxygen concentrations, cell potential, current density, and gas/cell-component temperatures. The current density distributions calculated by our simulation code were compared with the measured distribution by our segmented electrodes cell. The measured distributions under various operating conditions agreed well with the calculated ones showing that our code is reliable. The concentration overpotential through GDL was also estimated by the parallel fine pores model, but the estimated concentration overpotential was very small and could be neglected in the power generating performance of PEFC.

View full abstract

In order to keep power supply reliability at a certain level, electric power utilities have a certain amount of reserved capacity. When no generator outage or no unexpected large power demand occurs, however, the reserved capacity is regarded as surplus facility. To reduce the reserved capacity, some margin is reserved in tie lines between utilities. This margin is called Capacity Benefit Margin (CBM). In this study, a method of calculating optimal CBM in tie line under deregulated environment is described and two kind of optimal CBM are proposed. As a result, it is shown how the deregulation affects the optimal CBM by using numerical simulation for IEE Japan West 30 test system.

View full abstract

Recently, total number of distributed generators (DGS) such as photovoltaic generation system and wind turbine generation system connected to an actual distribution network increases drastically. The distribution network connected with many distributed generators must be operated keeping reliability of power supply, power quality and loss minimization. In order to accomplish active distribution network operation to take advantage of many connections of DGS, a new coordinated operation of distribution system with many connections of DGS is necessary. In this paper, the authors propose a coordinated operation of distribution network system connected with many DGS by using newly proposed sectionalizing switches control, sending voltage control and computation of available DG connection capability. In order to check validity of the proposed coordinated operation of distribution system, numerical simulations using the proposed coordinated distribution system operation are carried out in a practical distribution network model.

View full abstract

With recent development of power electronics technology, power system stability enhancement and optimal power flow control by using Flexible AC Transmission System (FACTS) devices have so far been studied. The FACTS devices to relieve multiple constraints can also make it possible to enhance Available Transfer Capability (ATC) without construction of new transmission lines. In this paper, a new method for improving transient stability by Unified Power Flow Controller (UPFC) is proposed. Then the proposed method is applied to an OPF control method by using UPFC for relieving multiple constraints. The new OPF method is used for enhancement of ATC taking into account Transient stability constraints as well as overload and steady-state stability constraints. The OPF problem is formulated to minimize total capacity of inverters of UPFC. Effectiveness of the proposed method is shown by numerical examples for IEEJ East-10-machine test system.

View full abstract

For considerations of risk managements of electricity market trading, this paper presents a time series analysis of the day-ahead spot price traded in the PJM power market, taking correlations among hourly price motions into account. The time series was decomposed into the deterministic and stochastic components, the latter of which was analyzed by using the AR-GARCH model both for hourly data (single-factor model) and daily data of hourly prices (multi-factor model), where hourly data were given as a series of hourly prices. The Monte-Carlo price simulation with resulting model parameters well reconstructed the original hourly time series. It was demonstrated to estimate optimum bidding prices in the day-ahead electricity spot market by using this price simulation for an example of its application.

View full abstract

This paper addresses a new robust control methodology to enhance the power system stability and voltage regulation as an integrated design approach. The automatic voltage regulation (AVR) and power system stabilizer (PSS) design problems are reduced to solve a single H∞ based static output feedback control problem. To determine the optimal gains, an iterative linear matrix inequalities (LMI) algorithm is used. A four-machine infinite-bus system example is given to demonstrate the efficiency of developed approach. The proposed robust technique is shown to maintain the robust performance and minimize the effects of disturbances, properly.

View full abstract

The authors have studied the frequency characteristics of synchronous generator equivalent circuit model. The authors examined the frequency characteristics of damper winding circuits using FEM. Then the new transient analysis method considering the impedance change with frequency is proposed during the transient phenomena such as out-of-phase synchronization using the electromagnetic transients program (EMTP-ATP).

View full abstract

Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuel. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which cause fluctuating power of wind turbine generator (WTG). In order to reduce the fluctuating power of WTG, this paper presents a output power leveling technique of WTG by pitch angle control using H_∞ control. H_∞ control is required to consider the measurement deviation and modeling error. The simulation results with using actual detailed model for WTG show the effectiveness of the proposed method.

View full abstract

Recently, because of the environmental burden mitigation, energy conservations, energy security, and cost reductions, distributed generations are attracting our strong attention. These distributed generations (DGs) have been already installed to the distribution system, and much more DGs will be expected to be connected in the future. On the other hand, a new concept called “Microgrid” which is a small power supply network consisting of only DGs was proposed and some prototype projects are ongoing in Japan.
The purpose of this paper is to develop the three-phase instantaneous valued digital simulator of microgrid consisting of a lot of inverter based DGs and to develop a supply and demand control method in isolated microgrid.
First, microgrid is modeled using MATLAB/SIMULINK. We develop models of three-phase instantaneous valued inverter type CVCF generator, PQ specified generator, PV specified generator, PQ specified load as storage battery, photovoltaic generation, fuel cell and inverter load respectively. Then we propose an autonomous decentralized control method of supply and demand in isolated microgrid where storage batteries, fuel cells, photovoltaic generations and loads are connected. It is proposed here that the system frequency is used as a means to control DG output. By changing the frequency of the storage battery due to unbalance of supply and demand, all inverter based DGs detect the frequency fluctuation and change their own outputs. Finally, a new frequency control method in autonomous decentralized control of supply and demand is proposed. Though the frequency is used to transmit the information on the supply and demand unbalance to DGs, after the frequency plays the role, the frequency finally has to return to a standard value. To return the frequency to the standard value, the characteristic curve of the fuel cell is shifted in parallel. This control is carried out corresponding to the fluctuation of the load. The simulation shows that the frequency can be controlled well and has been made clear the effectiveness of the frequency control system.

View full abstract

Superconducting generator (SCG) with superconducting field winding has many advantages such as small size, light weight, high generation efficiency. In particular, the property of low synchronous reactances, which is not realized in conventional generators, is able to improve power system stability. Installation scheme of SCGs in multi-machine power system becomes one of the topics that should be considered. It concerns how and where SCGs should be installed and parameters setting of machines and controllers. New methods for determining the optimal locations and machine parameters such as synchronous reactance X_d of SCG and control parameters based on approximated eigenvalue sensitivity and genetic algorithms for improving dynamic stability are proposed in this paper. Effectiveness of those methods are verified in IEEJ East 10-machine and it is shown that the proposed methods are effective installation schemes for improving power system stability.

View full abstract

Distributed Generation (DG) can provide several advantages to the distribution system. The advantages of DG can be achieved if the necessary concerns are strictly followed to prevent the unfavorable problems. It is known that voltage violation is the most important constraint for the maximum allowable DG. This paper takes into account the issue of system voltage profile, while the total DG is being calculated. In a number of cases, the total DG is limited since the system voltages are over or lower than the limits. This is because DG can cause the voltage fluctuation to the system. This voltage fluctuation due to DG may cause problems to the existing voltage regulation. However, DG itself can be used to regulate or support the system voltage profile if the installation has been well studied and carried out. With the varieties of dispersed locations, operating modes, and installed capacities, DG, in contrast, can be properly designed and controlled to help system voltages be maintained within their standard levels. This paper uses the varieties of locations, modes, and capacities to balance and maintain the system voltage profile to acquire the maximum total installed capacity of DG. The solution is achieved by the optimization process. Moreover, the issue of stochastic uncertainty of renewable energy resources is taken into account. Probabilistic Load Flow (PLF) is employed to ensure that the solution will be effective in the acceptable range of deviation. The analysis and discussion are presented as a feasible study for the system utilities or DG owners. The proposed method is applied with IEEE 34 Bus test system, and the numerical results show that the satisfactory system voltage profile is obtained as well as the maximum total DG.

View full abstract

In small power system, such as a black start of a power system, an overvoltage could be caused by core saturation on the energization of a transformer with residual flux. Such an over-voltage might damage some equipment and delay power system restoration. Through an actual field test and EMTP simulations, we have found that such phenomena cannot be accurately simulated using a normal transformer model with inductance data measured during the factory test. This paper proposes a new calculation scheme of transformer inductance by using actual field test data in order to grasp the saturated transformer characteristics accurately. We also show an analytical scheme for calculating the saturated inductances from shunt currents in delta windings that give extensive influence to over-voltage under flux saturation.

View full abstract

Generation expansion planning and transmission planning are strongly related. It is increasingly demanded in power industry to optimize such a generation-transmission planning so that whole power system can be operated in a more economic and reliable manner. So far most of existing methods are to either solve generation expansion planning or transmission planning due to the computational burdens, in particular for a large-scale system, and also there are no commercial packages available to solve such a problem directly. In this paper, we propose a bi-level model that divides the original problem into a master problem and two sub-problems. Optimization for such bi-level model is facilitated by using the long-term nodal marginal costs, which is acted as economic signals for the master problem and the sub-problems. To demonstrate the proposed method, we adopt several test systems, which verify the effectiveness of the proposed algorithm.

View full abstract

Recently, distributed resources are increasingly connected to distribution networks and management of the voltage distribution system has become more difficult. As a countermeasure, it is necessary to properly adjust the transformer tap setting of pole transformers in order to increase the ability to manage the voltage. However if the taps of a pole transformer is modified, it becomes necessary to reexamine and adjust the parameters of the voltage control equipment and to carefully arrange the equipment in the distribution system. Optimizing the configuration of the distribution system becomes more important, however, the problem is very complex and there has been no excellent solution until now.
In this paper, we propose a method to manage the feeder voltage of a distribution network by optimizing the pole transformer tap setting. The voltage profiles are calculated by load flow calculation under the several conditions that the load is heavy or light, the output of the distributed generators (DG) are maximum or minimum. The tap setting of the pole transformer, setting point of the step voltage regulator (SVR) and sending voltages of the feeders are decided in a way that satisfies the voltage constraint 101 ± 6V for each load condition. The problem is formulated as a combinational optimization problem. The optimum solution can be obtained by using branch-and-bound search method with effective bounding operations. The outline of the algorithm and calculation examples using a sample feeder are also described in this paper.

View full abstract

The “New Energy Plant” had been built at the Aichi EXPO. 2005 site as part of the “Demonstrative Project of Regional Power Grid with Various New Energies”. The plant includes three types of fuel cells, photovoltaic power generation system and Sodium Sulfur (NaS) battery. One of the purposes of the demonstrative project is to verify supply/demand control to minimize the effect on the utility grid. Isolated operation of a microgrid is an ultimate state to be no interaction between utility grid and the microgrid. It also increases value of the microgrid. These new energy generators and battery are connected to the microgrid via inverter and there are no rotating generators. There are no established techniques to startup and control voltage and frequency of such system. The authors carried out a verification test of isolated operation of the microgrid.
This paper presents the control strategies for isolated operation of a microgrid configured with some new energy generators. Simulation results of system excitation, load share operation, and response for load change such as an induction motor is connected are shown. This paper also presents the test result of isolated operation of a microgird on Aichi EXPO. 2005. The system had separated from utility grid, and performed stable controllability for load change for around three weeks.

View full abstract

This paper presents an Adaptive Particle Swarm Optimization (APSO) for Unit Commitment (UC) problem. APSO reliably and accurately tracks a continuously changing solution. By analyzing the social model of standard PSO for the UC problem of variable size and load demand, adaptive criteria are applied on PSO parameters and the global best particle (knowledge) based on the diversity of fitness. In this proposed method, PSO parameters are automatically adjusted using Gaussian modification. To increase the knowledge, the global best particle is updated instead of a fixed one in each generation. To avoid the method to be frozen, idle particles are reset. The real velocity is digitized (0/1) by a logistic function for binary UC. Finally, the benchmark data and methods are used to show the effectiveness of the proposed method.

View full abstract

Opened wholesale electric power market in April 2005, deregulation of electric power industry in Japan has faced a new competitive environment. In the new environment, Independent Power Producer (: IPP), Power Producer and Supplier (: PPS), Load Service Entity (: LSE) and electric utility can trade electric energy through both bilateral contracts and single-price auction at the electricity market. In general, the market clearing price (: MCP) is largely changed by amount of total load demand in the market. The influence may cause price spike, and consequently the volatility of MCP will make LSEs and their customers to face a risk of revenue and cost. DSM is attracted as a means of load leveling, and has effect on decreasing MCP at peak load period. Introducing Energy Storage systems (: ES) is one of DSM in order to change demand profile at customer-side. In case that customers decrease their own demand at jumped MCP, a bidding strategy of generating companies may be changed their strategy. As a result, MCP is changed through such complex mechanism. In this paper the authors evaluate MCP by multi-agent. It is considered that customer-side ES has an effect on MCP fluctuation. Through numerical examples, this paper evaluates the influence on MCP by controlling customer-side ES corresponding to variation of MCP.

View full abstract

Recently, basic framework of electric power systems has been changed greatly by deregulation of electric power industry. Independent Power Producers (IPPs) or Power Producer and Suppliers (PPSs) as new entrants are increasing in the power generation division. For power system stability, conventional electric utilities and PPSs have to take a balance between supply and demand. More specifically, PPSs maintain the difference between energy supplied by generators and energy consumed by demand within fluctuation range of the 30-minute balancing rule and, general electric utilities eliminate its imbalance in the whole power system.
This paper investigates PPSs' effects of retail wheeling from both sides of PPSs and a general electric utility. First, from the point of PPSs, it presents a control method of generators under the condition where PPSs produce electric power economically. And from the point of a general electric utility, it evaluates the generation capacity for load frequency control as effect of retail wheeling on the frequency control. The validity of the proposed technique and influence evaluation to the frequency control are shown by the simulation which MATLAB/Simulink is used for.

View full abstract

The authors have proposed Flexible, Reliable and Intelligent ENergy Delivery System (called “FRIENDS”), which is a new concept for future power distribution systems. Also, “Micro grid” which is the similar concept to FRIENDS has been developed. In Micro grid, on independent distribution system can be constituted by a number of distributed generators. In this paper, FRIENDS, Micro grid and conventional distribution systems are compared quantitatively in supply reliability and system cost through time sequential Monte Carlo simulations. In addition, for cost evaluation, interruption costs are included to show risk incurred by unsupplied energy. Finally, authors search for preferable form with install and operation of distributed generators and network composition according to social cost including interruption cost and system cost.

View full abstract

The Islanding detection device of the most important protection instrument for the Utility—Interconnected Photovoltaic inverters the islanding phenomenon by the influence of the resurrection energy of the motor load and the resonance load. In the main discourse, it experimented on the individual operation by both measurements, and compared the amounts of electric energy of the motor load and the resonance load using PCS of a real machine and the effectiveness of the motor load was confirmed.

View full abstract

In Japan, forest thinning residues as woody biomass have potential to increase domestic primary energy supply, because there still remain many conifer plantations where thinning is not carried out. However, taking the reduction in carbon stock in forests into account, the additional thinning for energy supply may not contribute to the reduction in CO₂ emission. Considering the change in the carbon stock in forests, this paper discusses the potential of reduction in CO₂ emission by biomass power generation with thinning residues. As power generation systems with thinning residues, co-firing with coal in a utility's power station and a molten carbonate fuel cell (MCFC) with gasification system are taken into account. The results suggest that the co-firing of woody biomass supplied by the additional thinning at utilities' coal-fired power stations has a potential for reducing overall CO₂ emission.

View full abstract

In the 21^st century, global warming has become a very serious ecological problem. It is necessary to prevent global warming from increasing the greenhouse effect gas such as carbon dioxide. A new energy saving technique using mechanical pump system is proposed as a solution to this problem. The pump carrying the water, which is the heat source, for the air conditioner has an effect on energy saving by using effective automatic control. Since there is a lack of knowledge related to mechanical pump, effective automatic control systems combined with some pumps are implemented only in a few buildings. In this paper, the machine characteristics of a mechanical pump and a system design combined with some pumps are applied to a decrease in energy consumption. Based on the characteristics of the pump, the automatic control techniques are constant discharged pressure control technique, estimated end pressure control technique and real end pressure control technique. In this paper, the estimated end pressure control technique is recommended as a result of testing the automatic control system combined with the pumps. Also, improvement in conditions of the pump is proposed as a new energy saving technique.

View full abstract

This paper presents the application of Independent Component Analysis (ICA) in power system. ICA is a method for finding unknown signals from observed ones. Given that observations are linear mixture of independent signal sources, then we can estimate signal sources from just only observations using ICA method. ICA is based on a linear-mixture model, in contrast, power system is a nonlinear system. However, applying DC power flow model, branch active power flows are represented as a linear mixture of active power injected into bus. DC power flow model matches ICA model. Therefore, in power systems, we can estimate bus injections from observed branch power flows using ICA. In this paper, we extend this idea to power estimation of Distributed Generation (DG) connected to radial distribution system. Note that ICA has two indeterminacies, scaling and permutation. To solve these matters, we use preliminary knowledge, DG maximum output power, connected node and network topology. We demonstrate the validity of this approach on a 69-bus distribution system, and then discuss the results with error analysis and spectrum analysis.

View full abstract

An electrolytic solution surface was used to simulate the surface of wet polluted insulators. When a local discharge propagates on the electrolytic solution under an impulse voltage, the discharge current flows in the electrolytic solution through the contacting surface between the local discharge and the electrolytic solution. Accordingly, a potential distribution occurs along the electrolytic solution. The authors examined the shape of the contacting surface between the local discharge and the solution. By using the shape of the contacting surface, an electric potential near the tip of the local discharge on the electrolytic solution was calculated. A source of the discharge current at the contacting surface is replaced by charge and the potential on the electrolytic solution is calculated with the image method. In this paper, the potential was measured along the solution in the low pressure air with a probe. The calculated values and the measured values of the potential agreed well regardless of the peak value of the applied voltage, the resistivity of the solution, and the waveform of the applied voltage.

View full abstract

The maintenance rationalization to the equipment under operation and the lifetime protraction based on appropriate diagnosis result are necessary for the reduction in cost of gas insulated equipment. Therefore, the accurate state observation method for inside of equipment is requested. In this research, the new state observation method which enabled the high sensitivity detection of decomposition gas by setting up the absorbent outside of the equipment was proposed. As the result, it was shown without ruining the reliability of the equipment by the absorbent unit setting up outside of the gas insulation equipment that the high sensitivity detection of decomposition gas is possible. Because the concentration of decomposition gas shows a remarkable correlation between total electric charge of partial discharge and the lifetime is different depending on the kind of the decomposition gas, the possibility that the detailed state of the equipment can be diagnosed was shown according to the detected gaseous species and its amount. Moreover, we succeeded in the detection of the decomposition gas from the absorbent, therefore the availability of this method was shown.

View full abstract

Waterproof layer is used to prevent penetration of water which is one of the factors of dielectric breakdown in XLPE cables more than 66kV class. A XLPE cable sheath with waterproof layer is done landfill disposal as industrial waste because separation of waterproof layer is difficult for technology and cost.
However, around 20 years passes after waterproof layer was introduced, and social consciousness for environment changes during these 20 years, and responsibility of company for environment of a society grows bigger. We report the result that examined techniques for separating waterproof layer.

View full abstract

An advanced analysis method for grid connected PV systems is developed in this research. To investigate the issues which may happen in the clustered PV systems, “Demonstrative research on clustered PV systems" is being conducted from December, 2002, in Oota, Japan. More than 500 residential PV systems will be installed in the demonstrative research area, battery integrated PV systems are developed to avoid the restriction of output power due to the raising of grid voltage. Annual performance of commercial PV systems without battery is analyzed and resulted in around 80% of performance ratio on the average. Over voltage of power distribution line and snow are two major factors of very low performance ratio on daily basis. Effects of batteries are also analyzed, the results indicate that there will be some improvement for the energy loss due to the grid voltage but PCS's efficiency will be around 8% worse than that of the commercial PV systems. It is also found that the non-optimized operation of battery sometimes results in the fully-charged situation during the noontime and maximum reverse power flow may not be minimized in this situation.

View full abstract

The national-standard-class measuring system for the impulse voltage measurements in Japan was developed in 1999, and its performance has been evaluated annually supported by Ministry of Economy, Trade and Industry (METI). The system has participated in the worldwide comparison tests and its good performance has been confirmed. The low voltage calibration system which is the part of the standard measuring system was compared among 4 countries in a different series of international comparison tests, and the domestically-evaluated low uncertainty of the Japanese system was proved to be reliable.
In this paper, the details and the results of the international comparison tests on low voltage impulse carried out in 2004 and 2005 are reported.

View full abstract

The present paper has investigated the effect of sheath grounding on a control cable based on EMTP simulations, when a lightning current flows into counterpoises representing a part of a grounding mesh. Voltages and currents observed on the control cable are given as a superposition of an well-known induced voltage due to the lightning current on the counterpoise, of a voltage transferred from the counterpoise to which the cable metalic sheath is grounded, and of a lightning current circulating in a closed loop composed of the metalic sheath and the counterpoise when the cable both ends are grounded. The induced voltage from the counterpoise is not necessarily dominant even in a long cable because the current along the counterpoise decreases rapidly as the distance from the sending end increases. Although the sheath grounding decreases the node voltage due to the induced voltage, but at the same time increases a voltage transferred from the counterpoise. The inductance of a grounding lead reduces a current flowing into the cable sheath during a high frequency transient, and thus a more current flows through the counterpoise. This results in a higher induced voltage to the control cable from the counterpoise.

View full abstract

At substations where shunt reactors are installed, when a ground fault occurs near the reactor, d.c. current flows from the reactor to the fault point. There are cases where circuit breakers installed near the reactor interrupt only the d.c. current from the reactor with long arcing times. In those cases, attention should be paid to the damage of the contacts.
This paper shows the investigation of the d.c. current interrupting performance for the 550kV one-break SF₆ gas circuit breaker. In the range of some hundreds amperes, the d.c. arc voltages with long arcing times of the 550kV one-break circuit breaker were measured. The d.c. current waveform and arcing time at the d.c. current interruption by 550kV one-break circuit breaker in the 500kV cable system were calculated. Interrupting test circuit for the d.c. current interruption was constructed in the high power laboratory. From the interrupting test results, it was made clear that the circuit breaker had a good interrupting performance after the d.c. current interruptions.

View full abstract

The time constants of the D.C. component of asymmetrical fault current are trend to increase. It is said that interruption capability of gas circuit breaker degrades at asymmetrical current interruption.
This paper shows the investigation of the interruption capability of 550kV one-break SF₆ gas circuit breaker at asymmetrical current interruption. Interrupting tests of asymmetrical current with time constant 100ms, 150ms were carried out in high power laboratory. At the interrupting tests, arcing time was changed due to the time constant of the D.C. component. From the interrupting test results, arc energy was calculated. Degradation of the interrupting capability at asymmetrical current interruption was investigated by using measured arc energy.

View full abstract

The lightning-induced voltage has been one of the factors for the insulation design of a power distribution line. The authors have developed a method of analysis of induced voltages where the Agrawal's model is adopted as a field-to-line coupling model. In this paper, the sparkover rate of a medium-voltage line associated with indirect hits is investigated based on numerical calculations and statistical analysis by taking account of the correlation between the peak value and the front duration of the return-stroke current waveform. Regardless of the intensity of the correlation between these parameters, the sparkover rate associated with a subsequent stroke is higher than that associated with a first stroke when the line is equipped with surge arresters. Furthermore, it is shown that the sparkover rate significantly decreases with the increase of the correlation coefficient. This demonstrates the importance of the study of the correlation between the return-stroke current parameters.

View full abstract

This paper investigates frequency-dependent parameters of a counterpoise which are identified from measured voltages and currents by a numerical optimization technique. Based on the investigation, the frequency characteristics of the impedance and the admittance are made clear. Then, Sunde's formulas of the frequency-dependent impedance and admittance, which are not widely used because of requiring iterative calculations to determine the final values, are compared with the measured results. It appears that Sunde's iterative formulas show a similar trend to the frequency-dependent parameters identified from the measured results, and can be adopted in a frequency lower than 100kHz. However above the frequency, the formula is case sensitive and is not reliable.

View full abstract

This paper presents the results of an investigation of the contamination flashover voltage characteristics of cylindrical polymer insulators with different core diameters under simulated rain. The specimens had the same or very similar shed profiles but different core diameters. On the contrary to the results obtained under heavy fog conditions, flashover voltages of transmission line insulator with the smallest core diameter were not significantly higher compared with those of station insulators having larger core diameters, such as station post insulators and bushing shells. The dominant flashover mechanism of hydrophobic polymer insulators under contaminated and rain conditions is water streaming along the insulator surface and the bridging between the adjacent shed tips by dripping water irrespective of core diameter. So, the flashover voltage of a contaminated cylindrical polymer insulator is not significantly influenced by its core diameter under rain conditions. Based on our investigation results, combined with the results obtained under heavy fog conditions reported in our companion paper (part I), it can be said that contamination flashover/withstand voltage tests may be conducted only under heavy fog conditions for evaluating polymer insulators having larger core diameters, while tests under simulated rain conditions as well as under heavy fog conditions may be necessary for evaluating transmission line polymer insulators having the smallest core diameter. The investigation results of flashover voltage characteristics of hydrophobic polymer insulators presented in this paper will be helpful in the selection, design and maintenance of polymer insulators for contamination areas.

View full abstract

An impulse voltage measuring system of which performance is able to regard as the national standard class in Japan was developed in 1999. The same year, international comparison tests of the impulse measuring system were carried out among 23 countries. The performance of the impulse voltage measuring system in Japan was excellent.
For this measuring system in Japan, some tests to evaluate various performances of the components were carried out and the overall uncertainty of the system was estimated after the international comparison tests.
In this paper, the national standard class impulse voltage measuring system in Japan is described and its measuring uncertainty is discussed.

View full abstract

In this paper, the flame spread and damaged properties of residual current protective devices (RCDs) by tracking were analyzed. Pictures of tracking process were taken by High Speed Imaging System (HSIS), and fire progression was observed by timeframe. During the tracking process of RCD, it seemed to explode just once in appearance, but in the results of HSIS analysis, a small fire broke out and disappeared repeatedly 35 times and a flash of light repeated 15 times. Finally, an explosion with a flash of light occurred and lots of particles were scattered. Electric muffle furnace was used for heat treatment of RCD cases. The surface characteristics of specimens due to heat treatment and tracking deterioration were taken by Scanning Electron Microscope (SEM). Chemical and thermal properties of these deteriorated specimens were analyzed by Fourier Transform Infrared Spectrometer (FT-IR) and Differential Thermal Analyzer (DTA). The carbonization characteristics showed different chemical properties due to energy sources, and the results could be applicable to judge the accident causes.

View full abstract

Many high-Tc superconducting (HTS) tape manufactures make an effort to improve the transport characteristics of HTS tapes. When AC or DC current flows in the HTS tape, AC or DC magnetic self-fields are induced around the conductor by the current and these self-fields affect on the AC loss and the critical current like the transport characteristics of HTS tapes. The spatial distribution and magnitude of the self-field are variable due to the neighboring materials on the HTS tape. In this paper, the relation between the transport characteristics and the self-field distribution of HTS tapes with paralleled ferromagnetic material (Ni tape) and/or diamagnetic material (BSCCO tape) is experimentally investigated. The self-fields according to the DC and AC transport currents were measured by hall probe with axial and radial magnetic field components. The critical currents of HTS tapes with paralleled the Ni tape are slightly decreased and the transport current losses markedly increased. However, the critical currents and transport current losses of HTS tapes with paralleled BSCCO tape showed more improved performance than those of single HTS tape. We explain these results using the change of the spatial distribution and magnitude of self-field on HTS tapes by the neighboring magnetic materials.

View full abstract

On UHV transmission line, it is known that the secondary arc extinction time after clearing fault arc will be long and there is a possibility of auto-reclosing failure. Connecting shunt reactors with a neutral reactor to the transmission line is one way to reduce the secondary arc extinction time. Double circuit transmission line requires consideration of inter-circuit capacitance as well as inter-phase capacitance, which causes difficulty in configuring optimal shunt reactor. This paper proposes a simple method optimizing the shunt reactors connected to the double circuit transmission line.

View full abstract