In Japan, since the development of large power system, there have been spontaneouse low-frequency oscillation and local mode oscillation. The conventional PSS has been applied to generators in trank power system as a measure to improve the damping power oscillation. However, it is difficult for this PSS to improve the damping power system oscillation because of the hardware and the design of fixed PSS control constants. It has therefore become necessary to develop a new adaptive PSS system. This paper explains the development of new adaptive PSS system and the simulation of low-frequency and local mode oscillation for this new PSS system.

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Electric load forecasting in power system is very important for insuring reliability and for economical operation. Especially, daily peak load forecasting and daily load curve for following day are the basic operation of generation scheduling. Therefore, many statistical methods and empirical methods have been conventionally used for such forecasting. However, it is difficult to obtain the accurate forecasting. Moreover, it has been difficult to construct a proper functional model and to investigate factors related to electric load and weather conditions.
This paper presents an electric load forecasting system using artificial neural networks. The system forecasts electric load curves for following day and current day using two forecasted loads previously, weather conditions and the information of holiday. The system has been practically used in the central load dispatching center of Tohoku Electric Power Co., since July 1998. The forecasting results show the effectiveness of the proposed methods.

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This paper presents a new parameter setting method for line drop compensator (LDC) and step voltage regulator (SVR) considering interconnection of distributed generators. The proposed method can generate sub-optimal parameter setting considering various loading conditions and power output of distributed generators. Several LDCs and SVRs are sometimes installed in practical distribution systems and coordination of the parameter setting for the LDCs and SVRs should be considered. Therefore, considering various loading conditions and the number of parameters for LDCs and SVRs, the target problem can be formulated as a large combinatorial optimization problem. The objective function is to minimize the difference between a predetermined target voltage and calculated voltages at several nodes and to minimize losses in the target distribution system. The method considers upper and lower limits of voltage at each node and upper limit of current at switches and lines as constraints. The method utilizes a reactive tabu search and an enumeration method for optimization tools. It narrows the appropriate parameter ranges using the reactive tabu search at the first stage. At the second stage, the method optimizes the parameter setting using a multi-stage enumeration method. The feasibility of the proposed method is demonstrated on practical distribution system models with promising results.

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This paper presents a distribution state estimation method considering practical equipment in distribution syStems. Practical equipment in distribution systems causes nonlinear characteristics in an objective function. Conventional distribution state estimation methods assume that the objective function can be differentiable and continuous. Therefore, considering practical equipment, the conventional method can not be applied. This paper propose a novel distribution state estimation method using the hybrid particle swarm optimization. The proposed method can find load values and distributed generation output values considering practical equipment. The feasibility of the proposed method for the problem is demonstrated and compared with the original particle swarm optimization on practical distribution system models with promising results.

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This paper presents a long-term network expansion planning method for practical distribution systems. A long-term network expansion planning is one of the important activities in distribution control centers. Several objective functions, including new equipment installation cost, utilization rate, reliability, and loss minimization should be evaluated considering yearly increase of network loads and newly installed loads for each year at planning stage. However, only a few cases have been evaluated by experienced persons practically because of the limited planning time and it is difficult to evaluate the optimality of generated plans. This paper proposes a long-term expansion planning method considering new equipment installation cost, utilization rate, reliability, loss minimization, and yearly increase of network loads. The feasibility of proposed method is demonstrated on a practical distribution system models with promising results.

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Optimal power flow (OPF) with transient stability constraints is a nonlinear optimization problem in functional space which is not easy to deal with precisely even for small scale power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for the large scale power systems with a large number of transient stability constraints.

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This paper presents a practical algorithm for solving unit commitment (UC) problems with network constraints represented in Optimal Power Flow (OPF). The proposed algorithm is based on Successive Approximation Dynamic Programming (SADP) according to a Unit Decommitment Ranking (UDR) which is a priority list for unit decommitment procedure. The UDR can be determined by Dynamic Programming (DP) according to the information of OPF consisting a set of Lagrange multipliers (dual variables). Since the set of Lagrange multipliers represents the relationship between the optimal value of objective function and OPF constraints, the proposed algorithm can determine power system resource scheduling in consideration of network constraints, such as line flow and voltage constraints. The feasibility and effectiveness of the proposed algorithm are demonstrated on a modified IEEE Reliability Test System.

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For improving electric power system transient stability, synchronous generators in power systems are generally equipped with the controllers such as AVR, PSS, and GOV. Since various oscillation modes occur according to system conditions, such fixed controllers deteriorate the control performance.
We propose the adaptive power system stabilizer(PSS) using frequency domain analysis for improving electric power system damping. In the proposed method, at first, the frequency components of the generator's swings are detected by online FFT. The conventional PSS parameters are tuned online by a fuzzy controller based on the frequency domain analysis. We verify that the proposed adaptive PSS using frequency domain analysis can damp the generator's swings effectively.

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In this paper, a combined controller of Superconducting Magnetic Energy Storage (SMES) with series compensator for the stabilization of power system is proposed. The apparatus injects voltage of variable magnitude and phase in series with a transmission line and it is capable of absorbing or releasing energy from a generator freely. A new control scheme of this controller for the power system stabilization has also been proposed here. Under normal condition, it is controlled in order to compensate reactance by injecting voltage which has phase lagging behind the line current by 90°. When a disturbance occur, injected voltage from phase shifter is applied to the damping control of generator swing and the voltage regulation by using new concept. The active power control is contributed to the generator terminal voltage regulation and the reactive power control is contributed to the damping control of generator swing. When a large disturbance occurs, it is controlled in order to absorb the accelerating energy from a generator by using superconducting coil. This new controller apparatus is expected to be a promising fault current limiter because during a short circuit, the output voltage from series compensator is insignificant compared with the voltage across leakage reactance of series compensator. As a result, the proposed controller is expected to improve steady-state stability as well as transient stability. The effectiveness of the proposed controller is evaluated from the viewpoints of current limiting, transient stability improvement and steady-state stability improvement based on numerical analyses.

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Power demand is still increasing day by day in Japan although the economic condition is not so good. As a result power systems are becoming larger and more complex to meet power demand, and hence, power system stability enhancement is becoming more and more important. On the other hand, researches and developments on superconducting fault current limiter (SFCL) are moving forward in accordance with the advancement of superconducting technology, which are expected to be applied to practical power system. This paper describes the results of analyses about stabilizations of synchronous generators by SFCL under balanced and unbalanced faults occurred at different points, and the effects of malfunctioning and the quench time of SFCL on the generator dynamics

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Recently the wind power generation has attracted special interest and many wind power stations are being in service in world. In the wind power stations, induction machines are mostly used as a generator. Since induction machines also have a stabi problem like the transient stability of synchronous machines, it is important to analyze the transient stability of power system includ wind power stations. This paper presents a model of induction generators, develops methods of power flow calculation and transi stability simulation of power system including induction generators, and presents considerations on the characteristics of transi stability of induction generators on the basis of numerical simulations.

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Introduction of IPP and wheelings gives various influences to electric power systems. Especially, retail wheelings cause influences to reactive power balance and operating reserves and so on. Ancillary services for minimizing these influences to operate power system efficiently and stably are important.
This paper focuses on the ancillary services to estimate the influences by introduction of wheeling to power systems. Further, this paper tries to estimate that how retail wheelings give influences to power system operation, mainly from reactive power control and frequency control points of view. First, from reactive power control viewpoint, the influence on the transmission loss is evaluated by using Optimal Power Flow (OPF) calculation. Also, in case of providing the reactive power from IPPs, this paper proposes an index for evaluating the value of reactive power from the IPPs. Furthermore, from the frequency control viewpoint, this paper evaluates an influence of the wheelings on Load Frequency Control (LFC) capacity [MW] and LFC speed [MW/min] that electric power utilities should maintain a system frequency.

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The authors have already developed the Flexible, Reliable and Intelligent Electrical eNergy Delivery System (FRIENDS) as a future promissing delivery system. The most important function in FRIENDS is to execute customized power quality services by introducing Quality Control Center (QCC) between a distribution substation and electric consumers. Further, QCC can also supply a DC power directly using DC type dispersed generators such as fuel cell system (FC system), micro gas turbine (MGT). Therefore, if there are enough demands to the DC supply, introducing QCC or FC system (MGT) may give an economical value.
This paper considers a model of a quality control center which will be installed in an underground of an office building and analyzes the values of the DC supply using the model. Further, this paper proposes a method for determining the optimal capacity of facilities to be installed in QCC corresponding to the rate of DC demand to AC demand from an economical viewpoint. Also, this paper examines the optimal capacity of facilities to be installed in QCC considering the multi-quality power supply that classifies loads in the demand side according to the qualities.

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A physical-based model of a pn diode is extremely important for a successful design and development of not only electronic circuits but also power electronics systems such as a HVDC (high voltage direct current) system or FACTS (flexible ac transmission system), because the pn diode is a basic semiconductor device. This paper has proposed a pn diode model based on divided charge distribution for EMTP-type simulators such as EMTP and EMTDC. The proposed model physically represents drift and diffusion phenomena of a pn diode in model equations accurately to realize steady and transient characteristics including the forward and reverse recovery characteristics in the EMTP-type simulators. It has been also explained how the model parameters influence the diode voltage and current of the proposed pn model. With the diode voltage and current, the transient characteristic of the model variables have been also presented to understand a relation between the physical meanings of a diode and the model variables in the proposed model. Results calculated with a combined iterative method show a satisfactory coincidence with measured results.

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To search desirable energy pricing strategy which gives both of energy consumers and suppliers econotr incentives to mitigate environmental impact, analysis on the effect of energy pricing was performed. In paper, a total energy supply system in urban area which supplies all kinds of energy totally is considere Energy models of consumers and suppliers were developed to calculate the energy supply and demand the area. The energy supply and demand was determined to minimize the cost for consumers and suppliei Environmental impact and economic loss and profit was calculated from the energy flow as evaluation index of the energy pricing in order to evaluate the effect of the energy pricing quantitatively.

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Recent progress in microprocessor makes it possible to use real time Discrete Fourier Transform (DFT) with sufficiently short sampling period for the ac voltage phase detection. Though the frequency characteristics of the gain were already discussed by several authors, but the error of detected phase has not been discussed yet. This paper discussed about the phase detection error of DFT, and proposed the error correction scheme using the ac frequency. The required accuracy of the ac frequency for phase correction was presented in the paper. The authors used the phase obtained from DFT to calculate the ac system frequency and assessed the frequency error caused by the detected phase error. The presented system can suitably correct the phase detection error. They were expanded to the positive sequence phase detection of the 3-phase ac system. This paper also evaluates the suitability of the presenting error correction scheme to the 3-phase ac system.

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In the transformer insulation system, the oil gap is subdivided by pressboards. In DC insulation, higher field is applied to the pressboard having higher resistance compared with that of oil. There are a lot of pressboard joints in an actual insulated structure. The high field inside the pressboard transfers to other pressboard at the joint. This field transference causes high field concentration on creepage surface along pressboard. This higher field could trigger a creepage discharge. Regarding the field transference phenomena, we change condition of the pressboard joint and numerically calculate the field intensity caused at the joint in this paper. Discharge field strength is formulated by analyzing results of dielectric breakdown tests measured so far. These results allow us to offer an insulation design method about the field transference.

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When the thermoelectric generator is applied to the intermittently generated waste heat for the waste heat recovery, a heat accumulator enables a thermoelectric generator to reduce a generating cost. Because a heat accumulator stores a part of waste heat generated intermittently so that a thermoelectric generator can operate using the stored heat even while no waste heat is generated. On the other hand, when a thermoelectric generator is operated with heat stored in a heat accumulator, the temperature of heat source drops and causes decrease of generated power and conversion efficiency. So it is necessary to track the maximum point of net power, which is subtracted power required for circulation from gross power generation. In this paper flow rate control for maximum net power tracking of the thermoelectric generation with a heat accumulator is experimentally investigated with a commercially available thermoelectric generator. On the basis of the experimental result we evaluated the effect of introduction of a heat accumulator on performance of thermoelectric generation by use of intermittently generated waste heat on the view point of the rate of operation and generating cost.

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This paper proposes to use a multilevel converter configuration for back-to-back (BTB) HVdc Link. A multilevel converter is a kind of voltage sourced converter (VSV). IBC can control its reactive power independently from transmitting real power. Therefore, VSC has much better stability and controllability than conventional line-voltage commutated thyristor converter (LCC). However, VSC has some disadvantages. One is large switching loss. The cause of this loss is snubber circuit used for voltage balancing of series connected switching devices. A multilevel converter can reduce this loss since it decreases the number of series connected switching device and the switching frequency. We investigated the stability and controllability of multilevel converter used for BTB HVdc Link by computer simulation. The results show good stability in DC voltage and substantially quick response in real and reactive power control.

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Conventional voltage control on a distribution line has been carried out by Load Ratio Transformer (LRT) and Step Voltage Regulator (SVR). However, since the object of these control methods is slow voltage fluctuation, the high-speed voltage control system is required according to the spread of electronic equipment. This paper presents a series Static Voltage Compensator (SVC). It is possible to compensate momentary sag due to active and reactive power. The voltage control method is described and it is also shown that this technique makes possible co-operating work with SVR. Furthermore, the equipment built-in the voltage control method of a SVC is made as an experiment. The voltage compensation performance is verified by the connection with Real Time Digital Simulator (RTDS). In addition, a 75 kVA SVC is developed, and it was confirmed that the voltage control performance of a SVC achieved our desired end.

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The design strength of concrete pole is determined by wind pressure to overhead electric wire. The design value of wind pressure is decided by the value of wind pressure to electric wire as it becomes when the average velocity of wind is 40m/s.
If the wind pressure can be reduced, the cost for concrete pole and the damage to equipment from typhoon would be lowered and customer's service reliability would be incleased as well.
This research was made on a low wind-pressure electric wire that can reduce wind pressure the most in high velocity of typhoon wind at the speed of 40m/s to 60m/s by making grooves on the surface of insulated wire for overhead power supply line.The following are results:
(1) We found the shape of grooves that can reduce the wind pressure most in high velocity of wind at the speed of 40m/s to 60m/s comparing with the regular electric wire by wind tunnel test.
(2) In field including turbulence flow, the effect of reduce wind pressure by the low wind-pressure is good and the results is as good as wind tunnel test.
(3) The effect of wind pressure reduction is from 17% to 36% by using the low wind-pressure electric wire.

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Frequency converters are divided into two categories: rotating machine based frequency converters and semi-conductor based frequency converters. The frequency converters in the both categories require two rotating machines or converters whose capacities are nearly equal to that of their interchange power.
This paper proposes a new type of rotating machine based frequency converter which utilizes induction frequency converter and we call an adjustable speed induction frequency converter. The proposed frequency converter can drastically reduce the capacity and the losses of the conversion system and it can realize a compact and efficient frequency converter system. Firstly, the operational principle and control system of the adjustable speed induction frequency converter are described. Secondly, the simulation results of the proposed system are discussed. Finally, the preliminary design of 100 MVA adjustable speed induction frequency converter is presented and the comparison of the proposed system and conventional frequency converters is carried out.

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For Partial Discharge (PD) measurement, not only detecting the signal magnitude of PD is enough for evaluating the insulating constructions of HV equipment such as GIS, GIL, power cable, and cable joint, but also localization of the PD position is important to them. PD localization can help to find out the defect point effectively and determine the cause of PD, improve the manufacturing process, and increase the insulating properties. This paper describes multiple new methods of PD localization including 1) use of metallic foil electrode sensors, 2) excitation of X-ray radiation, 3) application of acoustic emission sensor, applied to a EHV prefabricated joint in a length scale of about 2m long. Comparing with the conventional PD localization for long size of cable, it is more difficult to locate a PD for the short size of joint due to the pulse reflection, the pulse propagating route and the difference of propagating velocity, based on the materials and shape of the part units of the joint. Several successful PD localization shown that the method can locate PD with sufficient accuracy.

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This paper describes a new developed automated partial discharge (PD) measuring system, which is not only for the small scale PD measurement of sample test in laboratory, but also for the large scale after-laying test of power cable line on site. The system comprises an 8-channel fast A/D transformer, a central signal processing unit and four computers, providing real time measuring for monitoring eight signals at the same time automatically. The judgment of PD or discrimination of PD and noise can be divided into three phases. In the first phase, PD judgment is executed automatically based on multiple signal gates: f-gate for frequency, n-gate for pulse count rate, q-gate for pulse magnitude, φ-gate for PD phase position, t-gate for continuous time, set logically in serial or in parallel. The alarm signal in this phase has three levels determined by the gate output. When an abnormal signal is detected the abnormal signal channel can be automatically fixed and connected to other sub-units, and the signal will be judged in the next phase. In the second phase, the abnormal signal will be recognized by three pattern discrimination units: a neural network based on the φ-q-n pattern, a multiple frequency pattern logic gate based on f-q-t pattern, and a statistical x pattern logic gate (x represented source position of the signal) based on x-q-t pattern. In the third phase, the operator can give a final judgment according to the summarized information including the original waveform displayed by oscilloscope, spectrum analyzer, and the signal processing results shown with more than six kinds of 3 D graphics by computer display. Furthermore, a helpful offline processing can give several kinds of serial graphics based on time history or voltage history to help observations and comparisons. The system has been put into practical uses for several PD measurements and all results have shown the system can perform with high sensitivity of PD detection and high accuracy of discrimination of PD and noise. In this paper, some examples of practical PD measurement on site are introduced.

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The experiment triggering rain by rocket scattering AgI vapor in cloud has been carried out from five years ago. The triggering effect has been observed sometime on the rader-echo with vertical cross section of raining space centered at the launching point of rocket. In the summer of 1999, the rockets were shot to thunder cloud, then heavy rain was triggered and also lightning was suppressed for a while.

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