Vacuum Circuit Breakers (VCBs) have widely been used for low and medium voltage level, because of their high current interruption performance, maintenance free operations and environment-friendly characteristics. The VCB is now going to be applied to higher voltage systems for transmission and substation use. In this paper, the recent technical trend and future perspectives of high voltage VCBs are described, as well as their technical background.
This paper presents the results of analyses of the effectiveness of a superconducting fault current limiter (SFCL) to stabilize the synchronous generators, suppress turbine shaft torque oscillations, and limit the fault current in a two-machine-infinite bus system. In this study, the system model with two SFCLs having shunt resistance installed at each generator terminal was used taking 3LG (three lines to ground) fault at 12 fault points into account. These analyses were performed using EMTP/ATP. It is concluded that the use of SFCL with shunt resistance value of 1.1 pu is most effective for all fault points for the stabilization of synchronous generators, the suppression of turbine shaft torque oscillations, and the limitation of fault current.
In recent years, the PMU (Phasor Measurement Unit) receives a great deal of attention as a synchronized measurement system of power systems. Synchronized phasor angles obtained by the PMU provide the effective information for evaluating the stability of a bulk power system. The aspect of instability phenomena during midterm tends to be more complicated, and the stability analysis using the synchronized phasor measurements is significant in order to keep a complicated power system stable. This paper proposes a midterm stability evaluation method of the wide-area power system by using the synchronized phasor measurements. By clustering and aggregating the power system to some coherent groups, the step-out is effectively predicted on the basis of the two-machine equivalent power system model. The midterm stability of a longitudinal power system model of Japanese 60Hz systems constructed by the PSA, which is a hybrid-type power system simulator, is practically evaluated using the proposed method.
The integrated energy service system for a specific area is supposed to deliver electric and thermal energy in an integrated manner for purpose of reducing cost, primary energy consumption and CO2 emission. Under an assumption of the service system, this paper develops a multi-objective optimization model for determining urban energy systems. Considering the various energy system alternatives, e.g. photovoltaic generations for residential houses and fuel-cell cogenerations for business and commercial customers, the model determines the share of the energy system alternatives in order to minimize the above three indices. As numerical examples, this paper illustrates tradeoff analyses in case that the proposed model is applied to 2 kilometers square of an actual city in Osaka. Finally, this paper illustrates the role of various energy system alternatives from CO2 reduction and fossil energy reduction points of view.
This paper addresses the problem of generation planning in the competitive power market with uncertainty of demand growth. The distributed generator (DG) is paid attention against a large-scale generator to correspond uncertain demand growth. Optimization consists in minimizing the average cost and hedging risk over the scenario trees of demand growth. At first, based on the idea of Real Option, Dynamic Programming using the utility function is applied to generation planning. Utility functions can model investor's risk-return profile. The decisions in the first stage indicate that they are influenced by the type of utility functions and demand growth scenarios, and data of generators. Next, Monte Carlo Simulation is applied to Brown motion model of demand growth. This model can increase the possible number of demand level. With this simulation, the case that the distributed generator has advantage against the large-scale generator is quantitatively discussed.
From the view of environmental compatibility, we attempt to develop switchgear without using SF6 gas. As an electrical insulation gas, we focused our research on the compressed air and pure N2, because of their minimum global warming potential. In this paper, we verified the impulse breakdown and impulse partial discharge characteristics under various non-uniformity of electric field. The experimental result shows that the breakdown voltage (BDV) of air is higher than the BDV of pure N2 gas under highly non-uniform gap condition. On the other hand, the discharge inception voltage of air and N2 were almost the same. Furthermore, first partial discharge (PD), leader discharge and its transition to the breakdown were successfully observed through the measurement of discharge current and light emissions under impulse voltage application.
Evaluation of lightning surge waveforms that actually enter into substations is important when investigating the test voltage of electric power equipment. The standard lightning impulse waveform (1.2/50μs) is used for factory tests. However, the actual lightning surge waveforms in actual substations are complex waveforms in which various different oscillations are superimposed. Investigation of insulation characteristics of equipment against the complex waveforms and the standard one has significant importance. We analyzed these waveforms entering actual substations with respect to the insulation characteristics of gas insulated switchigear (GIS). From the results, we defined four types of non-standard lightning impulse waveforms. Then non-standard lightning impulse voltage is generated by an equipment circuit which is consisted of an impulse generator (IG), R, L and C is analyzed with EMTP. Voltage time characteristics were evaluated from the obtained impulse voltages.
Effects of installed SDR (System Dumping Resistors) on the stability of open-cycle disk MHD generator and synchronous generator system connected in parallel to power transmission lines are numerically studied. Usually the SDR is used to absorb the output energy of synchronous generator and to get stability of the power transmission system when faults occur in the A.C. power transmission lines. In this paper, we propose to apply the SDR in the D.C. lines between the MHD generator and the primary side of connected line-commutated inverters. We show that the SDR is effective for the system stability by a time dependent numerical analysis.
In order to develop the environment-friendly transformer, the rapeseed ester oil which is vegetable oil was selected as the new insulating oil and various characteristics of rapeseed ester oil were investigated experimentally. These results showed that the basic characteristics of rapeseed ester oil surpasses as compared with mineral oil.
We propose reducing a thermal resistance of a thermoelectric module by using grooved interlocking plates to increase efficiency of a thermoelectric generator. V-grooved plate thermal contact resistances monotonically decreased with increasing surface contact area. Thermal contact resistances of copper and aluminum plates having five times the contact surface area of planar plates were a quarter and a third of the planar ones, respectively. On the other hand, thermal contact resistances of rectangle-grooved plates decreased in a complicated manner with increasing surface contact area. Electric power and efficiency of a module with aluminum V-grooved plates were 25% and 16% higher than those of the module with planar ones. These results are caused by the decrease of the thermal contact resistances in the interlocking plates.
High frequency model of transformer winding is used to analyze the voltage oscillations due to various excitations such as the very fast transient overvoltage which occurs at the time of disconnecting switch operations. Usually, a circuit of interlinked inductances and capacitances is used for this purpose, in which circuit parameters have to be properly determined. Those constants have been hitherto estimated taking the coil section pair as a unit. In the method proposed here, the section pair can be further subdivided. The time-domain calculation is conducted combining the frequency analysis and FFT technique. The voltage oscillations of the winding subjected to the lightning impulse are calculated. The correspondence with the experimental results is satisfactory. The response to a chopped impulse shows this method's applicability to high frequency analysis. Since the constants are calculated directly from the design parameters of transformer winding, this technique is particularly useful in developing and designing transformers.
The small scale wind turbines have been used as the stand alone power source for years. Particularly these days, there is an increasing demand for the small wind turbines, of the output below 1kW, as monuments and educational materials. It is recommended that wind turbines of a diameter under 1.0m must be the low blade tip speed ratio type, owing to problems of both safety and blade noise. In these circumstances, it would be necessary to develop the system characteristics of the micro wind turbines for the purpose of much higher performance in spite of having the low Reynolds number regions. Therefore, in this work, in order to clarify the optimum aerofoil cross section for the micro wind turbine, we carried out a wind tunnel test of the two dimensional aerofoils in the low Reynolds number regions. Furthermore, we conducted the calculation of the turbine's performance based on the result of this wind tunnel tests. The model blades are manufactured with the blade chord of 0.15m, the blade span of 0.6m, and the maximum thickness of aerofoil cross sections from 8% to 32%. The experimental Reynolds number is around 150, 000. From this work, we have clarified the performance of the aerofoil cross sections in the low Reynolds number regions. Our work further proves that the turbine outputs were strongly influenced by the performance of the aerofoil cross section.
To achieve a rational insulation design for transformers, it is important to evaluate dielectric strength against actually impinging on equipment on-site This paper deals with the dielectric characteristics of a turn-to-turn insulation model for oil filled transformer under non-standard lightning surge waveforms combined with oscillatory voltage. As the results‚ the breakdown voltages and the partial discharge inception voltages of a turn-to-turn insulation model under non-standard impulse wave forms are higher than standard impulse voltages.
To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes evaluation of field overvoltage waveforms and its applications using experimental data of insulation characteristics for single-frequency oscillatory waveforms and double-frequency oscillatory waveforms. As a result, it was obtained that the evaluation method based on duration for which applied voltage is more than 80% of peak voltage. This evaluation method can estimate the insulation levels for field overvoltage waveforms at these for standard lightning impulse waveform. Furthermore, this method was applied to evaluation of filed overvoltage waveforms. It was obtained that this method is applicative and has higher precision than conventional method for evaluation under experimental conditions.
This paper describes the capacitive current interruption capability of circuit breakers from the view point of flashover characteristics between contacts of breakers. Authors obtained flashover characteristics between contacts of breakers with short distance by comparing with new condition and eroded condition after 3 shots of T60 according to new JEC 2300 (1998) and new IEC 62271-100. By comparison of flashover characteristics and electric field calculation obtained by the measurement of new and eroded contacts, deterioration of the dielectric capability is of 10 to 20 %. Authors also conducted flashover tests for the contacts and nozzle after significant number of interruption. The total amount of interruption can be considered as the maximum possible interruption according to CIGRE research. The deterioration of dielectric capability is of 10 to 30 %.
Photovoltaic (PV) power generation is spreading steadily, and the dispersed PV array system is increasing from the architectural restrictions. In the case of dispersed array system, if the arrays are installed in a different azimuth or if the module that constitutes array is different, mismatching loss will be generated when a single inverter is used to convert the output of arrays, because of the difference of optimal operating voltage. The loss is related to the array configuration. However the relation between array configuration and power generation output is not clear. In order to avoid generation of mismatching loss, introducing a distributed inverter system such as string inverter system or AC modules system is considered. However it is not clear which is more advantageous between a distributed system and a concentrated system. In this paper, we verified the output characteristics of two different solar cell arrays with various strings, azimuths and tilt angles, and clarified the relation between array configuration and power generation output by the computer simulations. We also compared the distributed inverter system with the concentrated inverter system, and clarified the optimal configuration of PV system with different solar cell arrays.
It is well known that grounding resistance under huge lightning current injection has current-dependent characteristics, whose mathematical model was already proposed by Liew and Darveniza in 1974. In this paper, where our final goal is reasonable design for lightning protection of 500-kV transmission tower, we adopt the dynamic grounding-resistance model to MODELS-ATP simulation. The effect of the model for the lightning surge analysis on 500-kV transmission line systems is discussed in detail.