Flexibility expresses the extent to which a power system can change electricity production (supply) or consumption (demand) in response to variability and uncertainty. Introduction of renewable energy sources, such as photovoltaic and wind turbine, increases variability and uncertainty and might cause supply-and-demand imbalance. Therefore, a countermeasure for improving flexibility is needed. In this paper, flexibility of thermal power generators is evaluated by using the simulation model which can calculate the supply-and-demand imbalance. The parameters of operation/planning and equipment modification are changed in the simulation. Flexibility parameters regarding operation/planning include supply capacity” and spinning reserve”. The flexibility can be improved as these reserves are changed properly. Flexibility parameters regarding equipment modification include ramp-rate”, minimum output”, minimum operating time”, minimum shutdown time” and duration of start-up process”. The flexibility is high as ramp-rate” is fast, minimum output” is small, minimum operating time” is short, minimum shutdown time” is short, and duration of start-up process” is short. The simulation results reveal that flexibility can be improved by changing operation/planning and equipment modification.

Promotion of renewable energy such as a photovoltaic generation (PV) is accelerated in the world, however, demand and supply balancing and voltage profile in power system may become worse by generation of renewable energy varied depend on weather condition. Therefore, alternative resources for demand and supply balancing and voltage regulation would be required and hydrogen supplying equipment known as power to gas (P2G), which can regulate active and reactive power by self-commutation type converter is considered as one of alternative resources. The authors focus on a microgrid including hydrogen supplying equipment for participating demand and supply regulation market and regulating voltage profile in power system. This paper proposes novel method to operate effective and economically for contributing demand and supply regulation and voltage regulation and reveals regulation ability and economic effects obtained by contributing power system operation through numerical case studies in microgrid interconnected to power system.

In order to study electromagnetic transient phenomena occurring in power systems such as inrush currents or ferroresonance, an accurate and practical three-winding transformer model is required because the power system to be studied includes three-winding transformers in many cases. Although a star-circuit representation (Steinmetz's equivalent circuit model) is often used for these kinds of studies, it sometimes causes numerical instability because its magnetizing circuit representation is inappropriate. A magnetic circuit model considering iron-core topology is capable of eliminating the problem. However, the conventional three-winding magnetic circuit model does not match the leakage inductance measurements (short circuit tests) of the transformer to be represented. In this paper, we develop the three-winding magnetic circuit model which can match the leakage inductance measurements by making use of mutually coupled magnetic resistances. As a result of verification using a 500 VA single-phase three-winding transformer, it is indicated that the leakage inductance calculated by the developed model are in good agreement with those obtained by the leakage inductance measurements of the test transformer.

To utilize renewable energy systems (RES) as main generators in power system, power system operators need to maintain reserve power to compensate the uncertain output of RES, such as wind farms (WF). This paper focuses on the balancing group (BG) composed of WF and a pumped-storage hydro generator (PSHG). In the BG operation, power system operators need to schedule the operation of PSHG to minimize the imbalance risk caused by the prediction error of WF output while considering the system specific constraints of PSHG, e. g. the mechanical constraint on pump-up/down switching. This paper proposes a method to schedule the PSHG operation using the interval prediction results of the WF output for alleviating the imbalance risk the proposed scheduling scheme is formulated based on the linear programming. To verify the effectiveness of the proposed method, the amount of imbalance and the net generation of the BG were evaluated based on numerical experiments under two types of situations with different characteristics in WF output. The experimental results reveal the effectiveness of the proposed method.

After the end of the feed-in tariff (FIT) that promotes the introduction of renewable energy, the use of renewable energy is being discussed. We have developed a hydrogen utilization system which can store renewable energy. An energy simulation was performed when this system was applied to a building with the energy reduction rate as a constraint. As a result, we clarified the installed capacity when hydrogen utilization system can be selected economically, and found an effective equipment price factor.

Currently, the introduction of renewable energy is progressing globally toward the realization of a low-carbon society. Many studies have been conducted on voltage control of distribution systems. These methods are roughly classified into two methods based on the control target device owners. One is owned by utilities, other is customers. In this study, we propose an efficient voltage control method by coordinating utility owned device and customer owned device. In order to confirm the performance of the proposed method, simulations were performed on a model system. The simulation results show that the proposed system is able to control the voltage by coordinating use of utility and customer owned devices.

Off-grid distribution system would be a promising option for a marginally viable community. However, technical challenge regarding photovoltaic generation employment in an off-grid distribution system is its uncertain and fluctuating generation output, which would require larger energy buffer and regulation capability. In this paper, it is proposed a probabilistic operation scheduling method for an off-grid considering the uncertainties in photovoltaic generation output and electricity demand. The proposed scheduling method uses both the probabilistic power flow analysis and the optimal power flow technique. Effectiveness of the proposed scheduling method is validated through numerical case studies for the assumed test off-grid model.

The authors focus on a microgrid (MG) having hydrogen production processes as a part of demand. The studied MG consists of a photovoltaic (PV), a battery storage system, two different type electrolyzers, and electric/fuel steam boilers and supplies for the electric, thermal and hydrogen demands. This paper proposes detailed operation scheme which consists of two stages, namely, the day ahead scheduling and the real-time (RT) control. The day ahead scheduling optimizes the operations of system components in the next day based on the forecasts for PV output and demands. The RT control provides the actual control command to individual system component based on the actual PV output and demands monitored online. The effectiveness of the proposed scheme is ascertained through some computational case studies. Performance of the proposed scheme is evaluated in terms of the total energy cost, the curtailed PV output and the hydrogen production volume.

The renewable energy resource such as the photovoltaic generation and the wind turbine generation is rapidly spreading into the power system. The forecast of its output is utilized to the balancing operation of demand and supply. Since the forecast error causes the imbalance of demand and supply, it must be compensated in the real-time operation by conventional generators. In this paper, we focus the virtual power plant which is composed by the distributed photovoltaic generations and the battery. The battery charges or discharges the forecast error of output from the photovoltaic generation to reduce the imbalanced energy between the scheduled and the actual output. By the computational simulation, we analyze the relationship between the imbalanced energy and the capacity of battery. In addition, the marginal imbalanced energy is proposed to design the monthly required capacity of the battery.

Loss minimum reconfiguration technology has been studied well from the theoretical and computational perspectives in the past decades and is expected to implement to the real-world distribution systems. In the real-world implementation of loss minimum reconfiguration technology, one of the barriers is the preprocessing cost for modeling the physical characteristics of the distribution networks and grasping the spatio-temporal dynamics of the load in order to derive the expected energy loss based on the power flow simulation though it is desirable that this technology is applied to the site with high expected energy loss reduction effect preferentially, the above laborious preprocess for prioritization which requires to be conducted for all the existing distribution networks becomes a problem of rapid implementation. In this study, the authors discuss several statistical approaches for prioritization of distribution networks with high expected loss reduction effect, that does not require the exhaustive preprocess. Numerical experiments based on data acquired from the real-world demonstration test reveal pros and cons depending on the application situation of these prioritization methods.

In Japan, after establishing the control reserve market in 2021, a Merit-Order (MO) method based on cost per kWh of each generator will be applied to load frequency control (LFC). The conventional Ramp-Rate (RR) method dispatches LFC signal based on ramp-rate of each LFC generator. The MO method may increase frequency fluctuation compared to RR method, because the aggregated ramp-rate of all LFC generators is not fully utilized, which is the result of the change of LFC signals dispatched to some generators are different from the change of Area Requirement (AR). In order to keep frequency controllability as RR method, we propose an LFC signal dispatching MO method considering the change of AR. The effectiveness of the proposed method is evaluated by using the IEEJ AGC30 model. This study shows that the proposed method is able to reduce frequency fluctuation compared to simplified MO method, and to reduce operating costs compared to RR method.

A back-flashover due to a lightning strike to the top of a transmission tower or its ground wires can result in the power outage. The occurrence rate and seriousness of the back-flashover should be estimated for existing or planned transmission lines for lightning risk management of power systems. This paper presents a modeling method of crossarms in a Transverse Electro-Magnetic (TEM) delay tower model, which considers a non-TEM characteristic of the tower. The voltages generated across the insulator strings due to a lightning strike to the tower top are discussed based on the analysis results by the finite-difference time-domain method, the TEM-delay model, and the multistory tower model, which has been widely used, with referencing surge experimental results reported in the past. Then back-flashovers of a 77-kV transmission system are analyzed using the proposed and conventional circuit models, and these results are discussed with referencing a measured back-flashover reported in the past. Based on the above analyses and discussions, this paper shows that the voltages across the insulator strings have been underestimated by the conventional model, and shows the applicability of the TEM-delay model to lightning surge analysis in high-voltage transmission systems.

Accurately calculating the transmission-line constants of underground cables and gas insulated bus (GIB) is important for various types of power system simulations. When calculating the transmission-line constants of a three-phase enclosure-type GIB, the Cable Constants supporting routine of EMTP is usually used. However, this routine could cause numerical errors, since the proximity effect is ignored for the calculation of series impedances and shunt admittances. In this paper, a method for calculating the transmission-line constants of a three-phase enclosure-type GIB considering the proximity effect is proposed. Then, series impedances and shunt admittances are accurately calculated by the MoM-SO (method of moments with a surface admittance operator) and MoM (method of moments), respectively. In this paper, the proposed method is verified by experiments using the small-scale model of a three-phase enclosure-type GIB. Calculated results obtained by the proposed method agree well with the measured results.

This paper proposes daily peak load forecasting by a correntropy based Artificial Neural Network (ANN) using an adaptive kernel size method for reduction of engineering loads considering outliers. When outliers exist in the training data, estimation accuracy of daily peak load forecasting using a conventional least mean square (LMS) based ANN can be affected by the outliers. Therefore, engineers have to remove the outliers in order to improve estimation accuracy and it is a heavy burden to engineers. Although Correntropy has a possibility to solve this problem, adjustment of a kernel size has been a big challenge for correntropy. Effectiveness of the proposed method is verified by comparison with a conventional LMS based ANN using Stochastic Gradient Descent (SGD), a Correntropy based ANN using SGD with a fixed kernel size and a Correntropy based ANN using SGD with the conventional adaptive kernel size method.

Accurate PV power generation forecast using numerical simulations have been getting more necessary in terms of the evaluation of its influence to power grid and the maintenance of PV power plant. We introduced irradiance-dependent shunt resistor to so-called single-diode equivalent circuit model to enhance the accuracy of the model. Using proposed model, calculation accuracy can be greatly improved compared to conventional equivalent circuit model of PV modules.

In recent year, there is the example that oscillating overvoltage occurs by the lightning strike to transmission line, and the transformer in substation breaks down. Lightning surges at two 77kV substations have been measured from 1990 to 1993. In this paper, I analyze the lightning surge waveform measured at substation including the transformer winding and show the relationship between the voltage of transformer neutral point and vibration frequencies of surges. Then, I show an outbreak condition of the qualitative resonance-related overvoltage by a frequency and the waveform pattern using XTAP (eXpandable Transients Analysis Program) and show the result that I inspected about a suppression effect of the transformer neutral point voltage with transmission line arrester and neutral arrester.

The proportion of the lightning outages in all outages on 6.6kV overhead distribution lines is high with approximately 20 percent in Hokuriku area, and then the lightning protection is important to prevent the outages. Several evaluation methods of lightning protection measures of distribution lines have been proposed. However, the frequency of lightning strokes to distribution lines is not accurately considered in these methods, particularly in winter. In order to find out the actual frequency of lightning strokes to distribution lines, we have observed lightning channels using lightning-video cameras at Tonami plain in Hokuriku area. If a lightning channel is recorded by two or more video cameras located at different points, it is possible to locate a lightning stroke point by direction finding method. In this paper, we present the observation data of lightning channels recorded by the video cameras from November 2016 to October 2019. First, we evaluate the location errors of the video cameras. Then, since it is confirmed that the lightning stroke points can be accurately located by the video cameras, we estimate the frequency of lightning strokes to distribution lines by season from observation data.

This paper described optical phenomena of propagating partial discharges (PDs) including leader transition from streamer discharge in SF₆ gas under positive and negative standard lightning impulse voltage. The optical measurement was performed using by special optical instruments like a framing camera composing of three ICCD cameras with optical filters to obtain spatial- or time-resolved spectroscopic images, a streak camera for a streak image or streak spectrum with a spectroscope, and a phot-multiplier tube (PMT) for light emission intensity, together with PD current and applied voltage waveform measurement by controlling the gate timing of the framing and streak cameras. As a result, typical optical properties to understand the leader transition based on stem or precursor mechanism were clarified, and optical features to identify the streamer and the leader discharge as well as the precursor that has not yet led to leader transition were found. These new findings could contribute to better understanding of PD mechanism as well as improvement of PD diagnostics of gas-insulated switchgear.

This paper described leader transition properties of propagating partial discharges (PDs) in SF₆ gas under the negative standard lightning voltage application with taking into consideration of effects of Trichel pulses and displacement current flowing between the PDs intermittently generated and around the wave front of the impulse voltage. Also, the scaling laws related to critical charge amount Q_cr for the leader transition, leader step length ΔL and leader step time τ_LD were applied to the obtained results to discuss the applicability and difference in the polarity effect. As a result, the valuable negative PD's data to allow to apply the scaling las were obtained from this study. It was revealed that the distinctive displacement current, i.e. gradient of the wave front of the impulse voltage with relatively higher amplitude, and Trichel pulses during the negative polarity discharges can affect the leader transition, and change of the capacitance by propagating PDs also affects the leader transition as well as the scaling law with a parameter of dV/dt because the displacement current flowing thorough the discharge channel is influenced by the capacitance.

The finite-difference time-domain (FDTD) method has been frequently applied to simulations of lightning-induced surges in overhead power distribution and telecommunication conductors. The applications are classified into two types in terms of spatial dimension: 2D and 3D. About 30% of the simulations have employed the 2D FDTD method in the cylindrical coordinate system, which is computationally quite efficient compared to the 3D FDTD method. In the 2D simulations, the FDTD method is employed to express the distributed series voltage sources in terms of incident electric fields tangential to overhead conductors, to be incorporated in the equivalent distributed circuit of Agrawal et al. 's electromagnetic-field-to-conductor coupling model. There are two other representative coupling models that yield the same results as Agrawal et al. 's model does. One of the reasons for using the hybrid approach is that horizontal closely-spaced thin conductors can be represented easily by a distributed circuit. In many of the 3D FDTD simulations, the subgridding or nonuniform gridding technique has been used to represent horizontal closely-spaced thin conductors. About 70% of the FDTD simulations as of today have been concerned with induced surges associated with lightning strikes to flat ground, and about 30% with lightning strikes to the top of mountain, building, or tall object.

The Power and Energy Society Annual Conference was held online from Tohoku University in Sendai, on September 9-11, 2020. The total number of papers was 317, and sessions were 47. A panel discussion and a special lecture were also organized during the conference period. The number of participant reached 806. The conference was successfully completed with great contribution from all the participant. This report summarizes the conference.