Cost and primary energy consumption are investigated, imaging that a photovoltaic/solar heat/cogeneration system (here, it is called a proposed system) is equipped in a hotel and a hospital. The proposed system is operated using a dynamic programming into which hourly data of electric load, heat load, insolation intensity and air temperature during a year are input. In the dynamic programming, the objective function is the cost or the primary energy, i. e., the former case is the cost minimum operation and the latter case is the primary energy minimum operation. The proposed system is compared with a conventional system, a cogeneration system and a photovoltaic/solar heat system. The results of the cost minimum operation shows that the proposed system in the hotel (the floor area ratio: 1000 %, the heat storage tank : 50 m³) reduces the primary energy to 84% and the cost to 96% of the conventional system. And the proposed system reduces the primary energy to 91% of the photovoltaic/solar heat system and 92% of the cogeneration system. The proposed system with the same size in the hospital reduces the primary energy to 90% while increases the cost to 101% of the conventional system. The primary energy minimum operation reduces the primary energy still lower than the cost minimum operation, while increasing the cost a little.

View full abstract

A stability criterion for nonlinear oscillations in power systems is proposed. It consists of calculation of a limit cycle by application of Hopf bifurcation theory and nonlinear transformation of the coordinates using invariant manifolds. The proposed method is verified in a single-machine infinite bus system.

View full abstract

Abstract-Power generation systems using natural energy sources such as Wind Turbine Generators (WTGs) are attracting attention because they offer solutions to environmental problems and cost reduction. They need another power compensating system to control the fluctuating power. In this paper, we propose using a Battery Energy Storage System (BESS) for the power control together with the WTGs in a Hybrid System. Active-power response of BESS is defined at characteristics of generators and frequency of the power system. A simple model for the Diesel Engine Generator (DEG) is used to analyze when WTG is applied to the power system on an isolated island. This model is useful to define the power response of BESS. Performances of two 280kW Hybrid Systems using BESS and WTGs are confirmed on Hateruma and Tarama islands in Okinawa Prefecture Japan.

View full abstract

Composite insulators have not a few advantages over ceramic insulators on contamination performance, safety, handling and cost. This article presents the results of development of the termination for XLPE Cable using composite insulator instead of ceramic one. Study of the contamination performance and the behaviour against moisture ingress of the composite insulator is introduced, and also the results of the electric performance test and the line-to-ground fault test of the several composite insulator terminations are introduced.

View full abstract

A new approach for location of electrical faults along power transmission lines has been proposed in this paper. In the new approach, the electrical current signals of a fault at various locations along a transmission line are introduced into two fiber optical cables that could exhibit two different propagation speeds, and the fault location is found by using the time differences of arrival of the output signals from the two optical cables. To evaluate this approach, two types of experiments, one with square pulse generators for relaying the signals before being introduced into the optical cables and the other without any relay, have been carried out and the results show the location can be found with an error less than 10 m for a simulated power transmission line.

View full abstract

1Hz current signals can be detected when in-service insulation diagnostic measurement is used for the maintenance test of XLPE power cables. By using “transmission mode” and the water tree deteriorated XLPE cables, the author had disclosed the detection mechanism of the 1Hz current signals By using “generation mode”, this paper describes detection mechanism of 1Hz current signals of in-service insulation diagnosis of XLPE power cables. Two kinds of generation mode operation mechanism had been studied. One, non-liner voltage and current characteristics of deteriorated insulator and beat-down operation create 1Hz signal, and another create wide band frequency signals like void discharge which is not proofed sufficiently using dried deteriorated specimen.

View full abstract

The temperature of a transmission line conductor is one of the important factors used to determine its current carrying capacity. There are several standards and methods by IEC, IEEE, CIGRE and ICS on the calculation of conductor temperature. Apart from heat dissipation by convection where some differences exist, almost the same formulae are used in these standards and methods in calculating the other terms of the heat equation that is used in determining the conductor temperature.
In this paper, a comparison of how the heat dissipation by convection is assessed using these standards and methods is reported. In order to compare the conductor temperature obtained by calculation and that measured experimentally, laboratory experiment of temperature measurement of ACSR conductors was carried out under several currents, surface and wind conditions. In the calculation, CIGRE method is used because it is virtually adopted worldwide. Under low wind velocity, however, the difference between calculated and measured conductor temperatures is quite significant. A new equation is proposed in order to narrow the differences between the measured and calculated temperatures under low wind velocity conditions. By applying the probabilistic technique or approach, the proposed equation and the CIGRE method were then employed to assess conductor temperature using actual climatic and current data. This is to provide a wider basis for comparison.

View full abstract

This paper describes a modeling of dispersed energy market involving cogeneration systems (CGS) and tariff system with multi quality classes. Regional dispersed energy supply systems are expected to improve the energy efficiency and the environmental pollution issues since they provide electric power and thermal energy simultaneously. Electric power wheeling and thermal energy transportation expand their potential benefits. At the same time, multi quality electric power system is also proposed. These diversification of energy supply options can achieve higher economic efficiency in the context of economic theories. However, since the power distribution system is provided by the utility, the theoretical optimality derived by the perfect competitiveness is not guaranteed in the market. The imperfectness of market condition will affect the electric power price, wheeling price and the contribution of CGS. This study develops a simulation model involving three players, i.e. utility, cogenerator and consumer. Electric power wheeling, heat transportation, the capacity of CGS as well as equipment and equilibrium prices of electric power are solved simultaneously. Multi quality tariff system is also involved. The model deals with two different market conditions - the perfect competition and Stackelberg behavior employing two level optimization. The simulation results exhibit the various effects of market conditions.

View full abstract

The Ar-SF₆ inductively coupled thermal plasma (ICTP) at atmospheric pressure was successfully generated for different SF₆ admixture ratios in order to investigate the quenching effect of SF₆ injection on thermal plasma from the viewpoint of elucidating a remarkable interruption ability of SF₆. Spectroscopic observation was carried out to measure the radial distributions of the radiation intensity of Ar lines and temperature for the Ar-SF₆ ICTP. It was found that only 0.5% SF₆ injection caused a 1/2 decrease in the radiation intensity and 1000 K decline in the temperature on the centre axis at 10 mm below the coil end. A two-dimensinal hydrodynamic model was developed for Ar-SF₆ ICTP to simulate flow and temperature fields on the assumption of the local thermal equilibrium. The results obtained from the calculation indicated that a little SF₆ addition to Ar ICTP decreased high temperature area above 9000 K drastically. This temperature decaying tendency agreed with the experimental results.

View full abstract

Decaying process of an arc conductance around a current zero was theoretically calculated for gases of SF₆, N₂, O₂, Air, CO₂, H₂, He and Ar at a pressure of 0.1 MPa. The calculation was performed both for wall-stabilized arc sustained in an axial gas flow and for that in no axial gas flow. The time variation in the conductance of the arc burning in each gas was determined from a static conductance and an arc time constant. This arc time constant for each gas was obtained from the radius r_c of a conductive zone and a thermal diffusivity at the radial distance of r_c on the basis of Frind's theory. Calculation result for the time variation in the conductance revealed that for SF₆, O₂, H₂ and He the conductances of arcs sustained in the gas flow proved to decay extremely just around current zero with a passage of time. Furthermore, concerning the H₂ and He, the conductance for the case in absence of the gas flow also proved to decrease in a similar aspect to that for the case in presence of the gas flow. On the basis of the result obtained, the suggestion on the alternative quenching gas used in the circuit breakers was given.

View full abstract

This paper deals with the breakdown voltage characteristics of oil filled transformer insulation models under fast front short duration impulse voltages(FFSDV). Types of tested insulation models are an oil gap, a turn-to-turn insulation model and a section-to-section insulation model. Breakdown voltages of three kind models have been measured with standard lightning impulse voltages and FFSDV. As the results, the breakdown voltages of three kind models under FFSDV are 1.3_??_1.5 times higher than those under standard lightning impulse voltages.

View full abstract

The current carrying capacity of the overhead transmission line greatly influenced by the forced convection cooling from the conductor. The velocity of the wind to determine the current carrying capacity is, less than 1.0m/s, and it is a breeze area. Because of that, there are a few examinations for forced convective cooling by using the actual conductors from difficulty of handling of the breeze until now.
So, we started the investigation about the ralitities forced convective cooling from the conductors, using wind tunnel, which shows good characteristics in breeze. In the examination, temperature of conductor was measured as a parameter, wind velocity, wind direction, current, and conductor size. A tendency about rise in conductor temperature was grasped, and a new calculation technique could be established as that result. When this new calculation technique is used, it is possible that electric wire temperature is predicted more precisely. Therefore, it can reflect on employing equipment effectively

View full abstract

The effects of externally applied radio-frequency (rf) electromagnetic field on the non-equilibrium and the performance of a disk MHD generator were examined experimentally. As a preliminary experiment, the plasma production by applying the rf electromagnetic field was attempted in the disk generator (Disk-PIA), in which rf induction coils were embedded in one-side disk wall, under the conditions of no seeding, no flow and no magnetic filed. From the result of the preliminary experiment, it was confirmed that the argon plasma (_??_110Torr) was produced uniformly in the azimuthal direction by the rf electromagnetic field even in the presence of exposed anodes in the faced disk wall and metallic support at the disk center. In MHD power generation experiments with the Disk-PIA installed in the shock-tube facility, the increase in the electrical output and more indiscrete discharge attributed to the rf electromagnetic field were verified with well reproducibility for the first time.

View full abstract

Lightning strokes with a large amount of energy sometimes occur on the Sea of Japan coast in winter. Winter lightning often damages overhead power distribution lines, in particular, those supplying power to high structures located in mountainous areas. We have investigated the characteristics of lightning outages on such distribution lines in order to establish effective countermeasures against damages from winter lightning. The ratio of surge arrester damages with respect to all damaged installations on such power distribution lines is the largest of approximately 50%. We have experimentally examined the effectiveness of installing two sets of surge arresters in parallel on a single pole as a method for preventing distribution surge arrester damages. In the case of installing 2.5kA and 10kA rated arresters with different voltage-current characteristics in parallel, the 10kA rated arrester stop flowing currents, when the 2.5kA rated arrester discharge. The current finally flows into only the 2.5kA rated arresters. We have clarified that to install surge arresters in parallel is effective in reducing the energy absorbed by surge arresters if these surge arresters have the almost same discharge voltage and voltage-current characteristics.

View full abstract

In winter, high-energy lightning strokes sometimes occur on the coast of the Sea of Japan. This winter lightning often damages overhead power distribution lines, in particular, those supplying power to customers with a tall structure located in mountainous areas. We have investigated the characteristics of lightning outages on such distribution lines in order to establish effective countermeasures against damages due to winter lightning. The number of damaged surge arresters amounts to approximately 50% of all damaged installations on such power distribution lines. We have examined the effectiveness of installing an overhead ground wire for branching a surge current in addition to a conventional overhead ground wire as a method for preventing distribution surge arrester damages using the EMTP. Installing an overhead ground wire for branching a surge current over four spans with the grounding resistance of which is 30Ω can reduce arrester damages by half as compared with installing only a conventional overhead ground wire.

View full abstract