In future power systems that the reverse power flow or the fluctuation of power flow by a large amount of introduction of distributed power sources such as PV may affect the sensitivity of a protection relay against a fault, which may cause miscoordination between the protection relays.
This paper describes the overview of coordination between fault clearance relays and the estimation method of the coordination between protection relays we have been developing.

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A Photovoltaic (PV) system is expected as one of the promising countermeasures for the global warming and the environmental issues. However, generation output from PV system is generally unstable and unpredictable. Therefore, large penetration of PV systems may cause some serious impacts to the power system operation such as a load frequency control, a voltage regulation, etc. Estimation of the influences of PV system installation is becoming important, however, it requires simultaneous multipoint solar radiation measurements. The Japan Meteorological Business Support Center has provided the 1-min meteorological data observed in Japan, however, its solar radiation data includes quantization errors. This paper proposes a regeneration method for the solar radiation data including quantization errors. This paper also analyses the spatial smoothing effect of the global solar radiation fluctuations.

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A large number of Dispersed Generations (DGs) are expected to be installed in distribution systems. Therefore the state estimation is important problem for stable and reliable system operation. However, it is difficult to estimate the total power of DGs connected to a load-side system from a metering spot on the distribution line because at the metering spot only a sum of the active-power from various loads and DGs can be measured. In this paper, we propose an estimation method for unknown DG-outputs connected to a distribution system. This method enables to estimate DG-outputs by analyzing a power flow data measured at one spot using independent component analysis (ICA). The estimation by ICA needs the same number of observations as estimations. However the observation spot is extremely limited in existing distribution system. So we propose an estimation method which enables to estimate DG-outputs and load-changes from only an observation by using known information of load power and a priori knowledge of insolation.

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Voltage rise problem in distribution networks has been discussed as the foremost concern against the penetration of large amount of photovoltaics (PVs). As a solution of such problem, using voltage regulation facility such as SVC (Static Var Compensator) or Loop power flow controller are proposed. However, it might require major investments in the distribution network and that means the cost would be imposed on the nation.
In this paper, the authors focus on latent ability of the present distribution network and PVs to find solution against the problem and propose a low cost solution to mitigate the voltage rise by using constant leading power factor operation of PVs. The distribution voltages are calculated in case of increasing highly penetrated PVs, where it is very important to make an aggregated model of the distribution networks including loads and PVs. The authors aggregate a lot of loads and PVs by using an aggregation method called “Y-connection”. As a result of having simulated with the aggregated realistic model of distribution networks, the authors confirmed that using a combination of leading power factor operation by Q = -0.2P and LDC of distribution transformer make it possible to maintain adequate voltage without voltage regulation facility such as SVC.

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Integrating of wind power generation into small islands has been one of the demonstration projects in Okinawa prefecture. Since such integration could deteriorate power quality including frequency in an island grid, a frequency stabilizing system using flywheels has been installed into a small island. In order to establish a proper frequency stabilizing scheme for the small island, an accurate model of a diesel generator including governor is vital. Therefore, the model was developed based on the measured values of generator dump tests. A new frequency stabilizing scheme was also developed through time-domain simulation of the island grid model which consists of the above-mentioned diesel generator model and an equivalent load change representing wind power variation. The proper parameters of the scheme were derived considering role sharing between the diesel generators and the flywheels. The developed stabilizing scheme was applied to the flywheels in the island grid and revealed great performance for mitigating frequency variation.

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This paper describes the results of experimental investigation on the effects of damper winding of a 4-pole synchronous generator at the synchronous generator transient. It is known in the simulation that the damper winding acts effectively at the synchronous generator transient condition. However, experimental proof has not been performed yet. Then, experiments on damper effects were conducted in this paper using a laboratory-scale power system. The damper winding of tested generator consists of 5 damper bars each pole and the number of working damper bars can be changed manually. Damper currents at each bar were measured by a Rogowski coil. FFT analysis was applied to both damper currents and armature currents under different operating conditions. Relationships between damper currents in the rotor and armature currents in the stator were made clearer than before.

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In evaluating the uncertainty of the standard measuring system for lightning-impulse high voltage, which is composed of the standard voltage divider, the digital recorder and the calibrators, step-response tests of the standard voltage divider may be useful. In this paper, convolution algorithm is employed to calculate output impulse-voltage waveforms from measured step-response waveforms. The uncertainties of the peak-value measurement due to influence of a nominal epoch, uncertainty of the peak-value measurement due to dispersion of the AC scale factor, and uncertainty of the virtual front-time measurement due to long-term stability are evaluated. Furthermore, error of the virtual front time of output waveforms is discussed. The front part of the step-response waveform, t<T_30%, does not influences the error of the virtual front time. Therefore, for the standard voltage divider, step-response parameters, i.e. experimental response time, partial response time, settling time, and overshoot have almost nothing to do with the error of the virtual front time.

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This paper presents the possibility to generate the alternating current (AC) electrical power by using a linear MHD generator. The single-sided exciting winding of the generator is considered. Its structure consists of a channel, an insulator and stators. The channel type is a flat rectangular and the liquid flows along the channel as a conductor. The channel wall acted as an insulator separates the metal fluid and stator coil. The top stator winding of the generator is connected to polyphase systems. Under this condition, it can produce a magnetic field by means of time harmonics function in the same direction of the metal fluid. Energy in the channel is extracted by inductive coils at the bottom stator. An interaction between traveling wave and metal fluid is explained by finite element technique. The distributions of magnetic vector potential and magnetic field throughout channel are evidently shown in xy-plane. Power flow in an AC MHD generator is reported with magnetic Reynolds number and slip value. The optimized value of active power is suggested by small slip value as s < 0 and small magnetic Reynolds number.

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The grounding resistance of surge arresters (Arrs) for the lightning protection of power distribution lines is generally maintained below 30Ω in Japan. Therefore, electric power companies have been spending a large amount of money on the construction and maintenance of low grounding resistances. In this paper, the influence of grounding resistance on lightning protection measures is clarified for power distribution lines with both a ground wire (GW) and Arrs by EMTP analysis and experiments. These results showed that even if the grounding resistance of Arrs becomes high, effectiveness of lightning protection is hardly decreased. Moreover, the results indicated that it is more important for constructing a rational lightning protection system to install a lot of lightning devices on power distribution lines than to lower the grounding resistance of Arrs.

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