The Electricity Supply Industry (ESI) in the UK was nationalised in 1947 and remained so until privatisation in 1990. On Vesting Day (31 March 1990) the nationalised ESI in England, Wales and Scotland was replaced, in accordance with the 1989 Electricity Act, by 19 separate undertakings. In England and Wales these successor companies comprised the 3 generating companies (National Power, PowerGen and Nuclear Electric), the 12 Regional Electricity Companies (RECs) for supply and 1 Transmission Company (the National Grid Company plc) which included the 2 Pumped Storage stations. By the end of 1996 the power stations in England and Wales will be made up of almost 60 centrally despatched power stations (not including auxiliary gas turbines). Thirteen of theses will be owned by non successor companies. The NGC transmission system has a central role linking the generators and the suppliers in the ESI in England and Wales. The transmission is developed to meet the power flows of the NGC customers who use its transmission system to exchange electrical energy. NGC are required under Condition 10 of the Transmission Licence to annually produce a Seven Year Statement covering the seven succeeding financial years. This provides a detailed forecast of customers electrical demand and their view of the generation capacity expected to be available in each of the seven years and provides a view of the generation margin and the power to be transported from one area to another. The paper briefly examines the developments that have taken place since privatisation, the customer forecasts of generation and demand and identifies the uncertainty associated with planning the development of the transmission system to meet future customer needs.

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This paper discusses a power flow control mechanism for the “Open Electric Energy Network (OEEN)” which has been studied by the authors as a demand-side network suitable for a free market of electricity. The important concept of OEEN is that electric energy is treated like a packet of mail with the information about sender (power producer) and receiver (consumer). The control mechanism discussed in this paper is called “Electric Energy Router”, and which includes energy storage device. Electric Energy Router controls the storage device in such a way that the “electricity packet” reaches a specified consumer from a specified power producer autonomously and in the distributed manner. This paper shows that optimal control theory can be applied to determine the control action of Electric Energy Router. The obtained optimal control action minimizes the difference between consumer's load pattern and the Router's supply pattern under the inequality constraints of energy storage capacity, A numerical example is given in order to check the validity of optimal control theory application. Furthermore, in order to manufacture a small scale Electric Energy Router for experiment, its basic structure and power control performance are studied through the simulation studies.

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This paper presents an algorithm for determining an economical operation and introduction schedules of dispersed cogeneration sources in electric power systems considering energy storage systems (ESS). Generally, it is considered that ESS plays some important roles. More specifically, it works as a buffer for regulating the time gap between electric load and thermal load, and also as alternative peaking units. First, this paper defines an index for representing a possibility for introduction of the ESS considering thermal merits of FC system. Using this index, we can determine the optimal operation of the FC system including the ESS. Further, this paper develops an algorithm for determining generation mix considering both FC system and ESS. In this method, the whole generation mix problem is decomposed into two subproblems, i.e., an generation mix problem for generators and FC system and an operation problem of ESS, and each subproblem is solved successively.

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Investigated in this paper is the optimal capacity of photovoltaic systems (PV) from the economic point of view when connected to commercial power systems. Under the assumption that PV outputs at each time interval are given a priori the optimum size of PV capacity is determined as a function of their unit costs. The problem is of typical linear programming type but its solution was derived solely of theoretical analysis of the problem, first with the simplified assumption about system structure and time zones, and next expanded to more complex cases.
The results show that substantial reduction in PV cost is required to realize large scale use of PV in connection with the present power systems.

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Electricity wheeling is defined as the transmission of electric power from a seller to a buyer through a transmission network owned by a third party, and the wheeling will be brought into reality in a substantial scale by the deregulation of electric power industry.
One of the most important questions in the wheeling of electricity is how to set its service rate. It is necessary to set the proper wheeling rate in order to achieve the efficient management of the electricity network, and also in order to expedite the efficient introduction of independent power producers into the electricity markets.
We had already reported a methodology for setting the wheeling rate on the basis of marginal cost theory, but the time span was not taken into consideration in the previous paper. This paper describes the estimation of the long-term wheeling rate using a dynamic model, which includes capacity expansions both in power generation and transmission lines. The problem is formulated as a linear programming problem, and then, the applicability of the proposed method is demonstrated using a simplified network model.

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Electric vehicles are expected to be one of hopeful leveling loads for the difference between the peak time and the off-peak time of electric load. From a global point of view, increasing environmental concerns make us recognize the necessity of replacement of conventional gasoline car by electric vehicle. Due to the problems of the efficiency and the life time of the battery, it will take time to use electric vehicles in general. Electric vehicles are used only in the specialized small fields. Nowadays, automobile makers cooperate to invent advanced batteries for electric vehicle. Thus it is the time to develop appropriate infrastructure standards and technologies to make electric vehicles attractive to the consumers.
In this paper, we investigate closely the impact of electric vehicle on the electric demands, by assuming the analytical models of EV consumption. The charging characteristics cf the battery, the running performance and the practical driving distance of each type of car are used for this analysis. According to the scenario analysis, the simulations are clearly presented the impact of EV introduction using the practical day load duration curve in Tokyo cosmopolitan area.
The authors conclude that the electric vehicle is effective for load leveling under some sort of market regulations. If there is no regulation in the EV market, power shortage will occur on both nighttime and daytime because of the concentration of the nighttime charge and the quick charge.

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This paper proposes a new concept of an electric power delivery system of future decade. The power delivery network consists from a set of meshed networks spread out every demand side block (city or town). On the end point of the power line network, a quality improvement facilities (be referred to as “quality improvement centers”) are installed, and each consumer can select arbitrary quality of the electricity. Thus the system can achieve the multi-menu-services and non-interrupted power supply. The system contains the small scale energy storage and dispersed small scale power generation systems. A main circuit breakers consists of power electronics devices, and communication networks are fully installed so as to control the power electronics devices or power flow according to the systems situations or the fault situations. The communication network also control the demand side management. From the above, the proposed power delivery network is flexible and reliable. The intelligent facilities (computers) are installed in the control centers as well as in the quality improvement centers. They control the system as the most energy conservative one. In this paper, the system is named as FRIENDS (Flexible, Reliable and Intelligent Electrical eNergy Delivery System). The conclusion of this paper summarizes the major research areas which must be completed so as to realize the system.

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To make more efficient electric energy supply system, deregulation in power system is being brought into practice in various country. For example, Independent Power Producers (IPP), combined with wheeling, are introduced into power system. New strategy for utility decision maker should be introduced to cope with new situation.
In this paper, the price difference model, which represent a power system with IPP, is developed. The pricing strategy for power producers (including utility and IPP) is analyzed using game theory. As a result, it is made clear that the pricing strategy for utility must be chosen carefully considering consumer surplus. Also, since wheeling charge has a great effect on consumer surplus, it may not be taken as a strategic variable of utility.

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In this paper, we propose a calculating method of regional transmission capacity pricing based on the interconnection of Independent Power Producers (IPPs) to reflect the proximity of the demand site and to allocate transmission capacity cost. In our model, economic load dispatching (ELD) and power flow calculation are integrated to evaluate regional transmission cost. First of all, in the ELD process, the output of utility's generator and IPPs are determined by the law of equal incremental fuel cost under the total system load demand. Then, power flow of each transmission line in the power system is obtained by the DC method using these generation outputs. Finally, the transmission capacity cost and price are estimated by the proposed allocation rule that reflects the proximity of the demand site and the improvement of reserve margin in the network. The results of case studies show that our proposed method can be applied to the quantification of factors unrelated to cost such as demand side proximity when purchasing from IPPs. We confirmed that our proposed method is a candidate for actual implementation.

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Electric power systems have become large and complex year by year, and also the number of decentralized power sources is rapidly increasing. Therefore, for the guarantee of the high reliability and security, a decent-ralized control based on the decentralization of power system should be developed.
In this paper, first a decentralised system is constructed by looking over the whole system from the generator-bus with the largest power. Since the decentralized system is identified as a one-machine infinitebus power model system with AVR and GOV, the equilibrium point control proposed for one-machine system by the authors can be applied to it. Then, control inputs u_a•u_g for AVR•GOV are determined, and equilibrium points of the decentralised system can be moved by changing the feedback gains. Especially, the unstable equilibrium point is set in each near outside of limitters for AVR•GOV, and the stability in the limitters is guaranteed. Thus, it is shown that, by repeating the same steps for other generators, the decentralized control for the three-machine model system can be completed.

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Fluctuation of plasma properties in nonequilibrium disk MHD generators and its effects on generator characteristics are discussed by numerical simulation, taking account of the fluctuation of seed fraction at the inlet of the generators. Effective electrical conductivity and effective Hall parameter are reduced due to the fluctuation of plasma properties when the partially ionized seed appears. The reduction of these values deteriorates the enthalpy extraction ratio of generators. It is found that the deterioration of enthalpy extraction ratio becomes large when the external load resistance is around the optimum value. It is also found that the distributions of properties along the radial direction become smooth as seen in the experimental data when the fluctuation of seed fraction is taken into account.

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It was reported that breakdown might be caused by the small arc current at the poor contact between conductors in GIS.
The effect of a small arc current on the breakdown was investigated experimentally. In the experimental apparatus, a poor contact portion of GIS was arranged by a rod-to-plane gap with the arc current.
It was clear that the arc current played an important role on the breakdown in the gap at gas pressure of 0.3_??_0.4MPa. The hot gas produced by the arc and the deforming of the contacts due to the arc were the main factors of the reduction of the breakdown voltage. The breakdown voltage was dependent on the arc current, and its reduction ratio increased with arc current. When the arc stopped, the breakdown voltage recovered to the level determined by the deforming of the contacts in a short time. The effects of the contact deforming and the hot gas on the breakdown voltage reduction could be separated by renewing the filled SF₆ gas after the duration of small arc current.

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A New type of pulsed transformer is proposed to apply for pulsed power technology as an alternative of a Marx generator. The transformer is constructed of a coaxially shaped ferrite core and a spiral winding of strip conductor. Transformer of output voltage more than 1 MV is demonstrated to be possible to design with winding ratio of 10:1 and residual inductance of secondary winding of 2.5μH. The performance of the transformer is demonstrated by the example design of the system where output pulse of 1 MV, 100 kA, 50 ns is produced by using 100 kV of 1st stage capacitor bank.

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To evaluate the suitability of the DC withstand test for use as the after-laying test for extrahigh-voltage XLPE cable lines, especially 500-kV XLPE cable lines, we studied the effectiveness of the DC withstand test and the influence of DC voltage application on AC insulating performance, using XLPE cables with artificial defects. DC breakdown strength of the cable with defects does not decrease radically compared with AC breakdown strength due to space charge effects. The defects that are detected by the AC withstand test might not be detected by the DC withstand test and short-circuited trees may appear at earthing after the DC withstand test, degrading the AC insulating performance. The DC withstand test should therefore not be used as the after-laying test for 500-kV XLPE cable lines.

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We investigated the diagnosis of insulation performance in SF₆ gas insulated apparatus like GIS. We performed time-resolved partial discharge (PD) measurements in SF₆ gas using a matching circuit and a digital oscilloscope for a needle-plane electrode arrangement to investigate the frequency component of PD current pulse. We also measured phase-resolved frequency characteristics of PD pulse in SF₆ gas using a spectrum analyzer. The experimental results revealed that PD pulse waveform differed depending on the voltage phase angle even when the magnitude of applied voltage and gas pressure were constant. This means that the frequency component of PD pulses differed depending on the polarity and the phase of applied ac voltage.
Consequently, we pointed out the necessity to select an appropriate frequency range for PD measurement depending on the frequency component of PD pulse.

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Joule dissipation in a nonequilibrium MHD disk generator was successfully estimated from power gener-ation experiments. Faraday current in the disk generator was measured. The reduction of the total pressure caused by the Joule dissipation was also estimated. Experimental results suggest that the isentropic efficiency of the generator is strongly affected by the value of the Joule dissipation.
When the applied magnetic flux density increased, the extraction of electrical power increased remark-ably, however the total pressure loss caused by the entropy production was suppressed. The high MHD interaction caused by the high magnetic flux density did not deteriorate the performance of the generator. It is considered from this fact that the application of higher magnetic flux density is essential to get higher isentropic efficiency.

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Islanding of the utility interconnected photovoltaic (PV) systems mainly installed in residential houses is a most serious problem for safety of utility distribution lines. Output power variation method is one of the recommended measures in the Japanese guidelines on utility interconnection. However, the effectiveness of the measure decreases in the case of parallel operation of PV systems because of a counteraction of output power variation from each system. A new output power variation method applicable to parallel operation of PV systems was examined in this paper through simulation studies, using the simulation method developed based on demonstration tests in Rokko Island. The major results of the study are follows:
- A new output power variation method was proposed in order to match frequency and phase of power variation among PV systems. In the method, phase angle of inverter output current is continuously modulated with instantaneous voltage signal of distribution line.
- The simulation results on the proposed method shows that even when a number of PV systems are operated, islanding can be prevented securely while maintaining power quality of inverter output in nomal operation. This suggests that proposed output power variation method can be applied to actual field.

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Numerical calculations were made on a nonequilibrium plasma and a MHD flow in a disk MHD generator with high MHD interactions. Main objective of the present study is to develop a numerical simulation model which can predict performance of a closed cycle disk MHD generator. The basic equations were quasi one-dimensional equations which govern the behavior of both the nonequilibrium two-temperature plasma and the MHD flow. TVD MacCormack method was first applied for the present system. The steady and stable solutions under wide operating conditions of the generator were obtained owing to the high resolution and stable TVD scheme. The distributions of several physical quantities and the basic performances were predicted and agreed well with our experimental data. A shock wave was induced in the nozzle where an ionization proceeded rapidly. As a result, the stagnation pressure loss reached 45_??_55% at the inlet of the MHD channel. Furthermore, the large stagnation pressure loss at the exit of the MIND channel which was observed in the experiment was predicted in the present calculation.

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In high voltage aerial distribution systems, insulated wires are supported by insulators. If overvoltages caused by lightning occurr in the central line of an insulated wire, creeping discharges progress along the wire surface from the free end of the binding wire and bring about an accident such as punch-through breakdown, disconnection of wire. The clarification of breakdown phenomena in these insulation systems will contribute to the prevention of such accidents. These creeping discharges can take on complicated phenomena due to the change of the electric field intensity on the wire surface so that the potential of the central line of wire is changed by induced lightning.
In this paper, we report the influence of the voltage change of the central line on lengths and aspects of creeping discharge when a standard impulse voltage is applied to the central line or binding wire.

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