摘要:

AbstractThis paper describes the development of dc XLPE cable. Through a series of material investigations, an XLPE compound containing highly purified special filler was developed.To check the dc insulation performance of the cable insulated with this new material, a prototype cable with 9 mm insulation thickness was manufactured. It was confirmed that the performance of the prototype cable was excellent. Based on the study of the prototype cable, a 250‐kV dc cable with 20 mm insulation thickness was designed and manufactured. Through a series of voltage tests, excellent dc insulation performance of the developed cable was verifie

ISSN:0424-7760    

DOI:10.1002/eej.4391140801

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes the development of the reliability analysis system for transmission systems from primary substations on high‐voltage trunk line systems to distribution substations. This system has been developed on an engineering workstation. The user can input the network data of power systems from primary substations to distribution substations and the structure of buses and connections of transformers in substations using graphics. This analysis system can evaluate reliability at each distribution substation by simulating outage and recovery process for all fault modes which can occur, defining the capacity of facilities, probability of fault at each facility, the value of load at each bank, and the points where switching elements are turned off in the network as input data. In the calculation of the recovery process of each fault mode, the constraints of operation of radial power systems are considere

ISSN:0424-7760    

DOI:10.1002/eej.4391140802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWith present‐day global environmental and energy problems, high expectations exist for solar power generation to reduce carbon dioxide generated by the consumption of fossil fuels.On the other hand, power consumption in residential homes is increasing every year. Among the many household appliances, the power demand for air conditioners increases dramatically during the summer, particularly in the afternoons. Since this pattern closely matches the output pattern of solar cells, it should be possible to combine a photovoltaic array with an air conditioner to decrease the energy consumption within the home.In this paper a residential solar‐powered air conditioner is developed that operates through a combination of photovoltaic array and commercial power. Also, the configuration and specification of the solar‐powered air conditioner are described, and its performance characteristics are examined by analysis of the characteristics of the solar

ISSN:0424-7760    

DOI:10.1002/eej.4391140803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn general, electric power companies must prepare power supply capability for maximum electric load demand because it is very difficult at present to store electric power. It takes several years and requires a great amount of money to construct power generation and transmission facilities. Therefore, it is necessary to forecast long‐term load demand exactly in order to plan or operate power systems efficiently. Several methods have been investigated so far for the long‐term load forecasting. However, because the electric loads consist of many complex factors, good forecasting has been very difficult.This paper proposes a long‐term load forecasting method using a recurrent neural network (RNN). This is a mutually connected network that has the ability of learning patterns and past records. In general, when interpolation is used for unlearned data sets, the neural network provides reasonably good outputs. However, when extrapolation is used, such as in long‐term load forecasting, some kind of tunings have been necessary to obtain good results. Therefore, to solve the problem, a method is proposed in which growth rates are used as input and output data. Using the proposed method, successful results have been obtained and comparisons have been made with the conventional

ISSN:0424-7760    

DOI:10.1002/eej.4391140804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe power supply system for a metropolitan area consists of multiple 275‐kV power cable systems to supply power to a large number of consumers. Each system has a large charging capacity (capacitive reactive power). When 275‐kV power cable systems experience a voltage drop, their charging capacity decreases. However, the reactive power losses increase in the 275‐kV overhead transmission lines, which supply large power to power cable systems, thus causing the performance of the power supply system to deteriorate.In this paper, the following three points are reported:1When the secondary power system of the trunk substation is a large‐scale power cable system, new techniques can greatly improve the voltage and reactive power characteristics by controlling the rise of the sending‐end voltage at the secondary side of the trunk substations and maintaining the voltage of power cable systems at a constant level.2In the use of this control technique, it has been demonstrated that controlling by the direct‐detecting method of a voltage drop in the primary power system is superior to one that controls by the indirect‐detecting method, which increases load power in the cable system.3The results of simulations obtained by using a 275‐kV cable system model and a performance power system model show that the use of this control technique can produce a good effect despite the allowances made for the opposite effect, i.e., a decrease in the capacity of power capacitors resulting from voltage drop at the tertiary voltage of a 500‐kV transformer.This study is carried out to examine the possibility of lightning control using a photoionized plasma produced by a UV laser without an optical air breakdown. As the fundamental experiment, the characteristics of a laser‐triggered spark gap (LTSG) are examined, where a laser beam is not irradiated on the surface of the electrodes. In this experiment, the KrF excimer laser is very effective in increasing the plasma densityneand the reduction ratiopof 50 percent breakdown voltage against the self‐breakdown voltage. The relation betweenneandpis increased by generating a long and high‐density plasma parallel to the discharge axis.On the other hand, the abnormal discharge process in triggered lightning using a rocket is examined, and it is indicated that the most important condition to trigger a lightning discharge is the production of a plasma channel of length 200 m and density about 1019m−3. It is suggested that such a plasma channel could be produced by a KrF excimer laser with an en

ISSN:0424-7760    

DOI:10.1002/eej.4391140805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractWith the progress of superconducting wires for ac power use, research on superconducting power transformers is increasing. These transformers can be divided into two types: the iron‐core type [1, 2]; and the air‐core type [3–9]. The latter type has such advantages as absence of iron losses and magnetic saturation, and greater possibility of reduction of size and weight. However, the air‐core transformer has a large magnetizing current due to the absence of iron core. Hence, research has been carried out on the possibility of using the air‐core transformer also as a shunt reactor in a power transmission system. However, the operating characteristics of the air‐core transformer, such as voltage regulation and reactance voltage, are not clear at present.In this paper, the equivalent circuit without losses is proposed first. Since this equivalent circuit is expressed by means of the magnetic coupling factor and self‐inductances of windings, the effect of these parameters on the transformer characteristics can easily be investigated. Then, based on this equivalent circuit, the per‐unit expressions for the air‐core transformer characteristics are derived and the characteristics are analyzed in detail. The validity of the theoretical results are confirmed by experimental results obtained by the use of an experimental supercondu

ISSN:0424-7760    

DOI:10.1002/eej.4391140806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractFor the optimum design of photovoltaic power systems, it is very important to estimate their annual maximum amount of output. In general, the annual maximum amount of output has been calculated by using photovoltaic module efficiency under irradiance of 1 kW/m2at AM 1.5 with solar cell temperature of 25°C. Since the spectral distribution of solar radiation changes with weather, season and time, the efficiency of solar cells is not always constant.This paper describes a method evaluating the maximum amount of output in photovoltaic modules, ‘the spectral method,’ by using the measured annual spectral solar radiation and the spectral response of various photovoltaic modules.The calculated values using the spectral method agreed well with the measured values for amorphous silicon photovoltaic modules from March 1991 to February 1992. The spectral method proved most effective for optimum design of amorphous silicon photovoltaic power sys

ISSN:0424-7760    

DOI:10.1002/eej.4391140807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes low torque pulsation and high‐power control of permanent magnet synchronous motor (PM motor) with distorted electromotive force (emf).The experimental model of PM motor is a 40‐kW, 190 r/min, salient‐pole, six‐phase machine. An individual single‐phase transistor inverter is connected to each phase of PM motor as a power source. By adopting full pitch and concentrated winding in the armature of the motor, the rate of flux utilization and output torque per mass can be increased. This winding causes trapezoidal distortion in the phase voltage waveform at no load. For realization of high‐performance control of PM motor, the current waveform should be determined so as to minimize torque pulsation and to maximize the output torque of the motor under the rated current.This paper proposes also the method to determine the optimum current waveform. The currents and emfs are expressed as N‐dimensional vectors (N: the number of phases). Due to the characteristics of the particular structure of the motor, the armature reaction is small enough to be neglected. In this case, the optimum current vector can be derived under two conditions: (1) the direction of the current vector always agrees with that of the emf vector; and (2) the scalar product of the two vectors is held constant. Supplying the optimum current vector provides no torque pulsation and the nearly maximum output torque under the rated current. This method also can derive the new optimum current corresponding to open‐phase operation.The validity of the method is confirmed experimentally. The characteristics of the experimental model of PM motor also are describe

ISSN:0424-7760    

DOI:10.1002/eej.4391140808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe important design factor of a superconducting generator is estimating the electromagnetic forces at the rotor dampers on a sudden three‐phase short‐circuit. In this paper, the armature current and electromagnetic forces on such a short‐circuit are simulated directly by two‐dimensional transient analysis, considering the following complex terms: 1 induced current by the speed electromotive force caused by the rotor rotation; the connection of three‐phase windings; and 3 the resistance and reactance at the armature coil‐end.The speed electromotive force is considered by using the combination method, which is FEM combined with BEM at the air gap. The connection of the armature winding and the effect of the armature coil‐end are considered by using the analysis combined with the external circuit equations. Moreover, the effect of the Röbel transposition of the armature winding is approximately considered.As a result of analysis, the electromagnetic forces at the rotor dampers can be calculated with a

ISSN:0424-7760    

DOI:10.1002/eej.4391140809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractParametric oscillations which occur in a nonlinear two‐phase circuit with nonlinear reactors and capacitors are applied to many kinds of power devices. When the devices are operating under light load, the output voltage of these devices exhibits unstable oscillations, i.e., subharmonic oscillations, quasi‐periodic oscillations or chaotic oscillations. This paper analyzes the abnormal oscillations and confirms the validity of the analysis experimentally.In this paper, new circuit equations are presented that can be applied to the analysis of a two‐phase nonlinear circuit in which reactor saturation curves are sharp. It is clarified by this analysis that the parametric oscillations of the circuit which contains reactors of moderate saturation characteristics become subharmonic or quasi‐periodic with the existence of resistances of the power supply side. Also, when the nonlinearity of the reactors in the circuit is sharp, the parametric oscillations may change into chaotic oscillations in addition to the aforementioned oscil

ISSN:0424-7760    

DOI:10.1002/eej.4391140810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY