Recent tendencies of installation surroundings and progress of technologies for environment load reduction on high voltage circuit breakers are reviewed. Damage situations of the circuit breakers on the Great East Japan Earthquake in 2011 are shown and studies of seismic design and guidelines of substation equipment are reviewed. In addition, new surroundings such as an offshore substations for wind farms are introduced. Life extension technologies with RCM (Reliability Centered Maintenance) will be more important technologies for a point of view of environment load reductions. The transition from fundamental phase to industrial phase will be made in research and development of substitute SF6 GCB (Gas Circuit Breaker).
There is a growing need to use photovoltaic (PV) technology to mitigate global warming and the depletion of fossil fuels while also enhancing energy security. However, the high network penetration of PVs has various negative effects on electrical power systems. In recent years, automated operating systems have been introduced into substations to enable rapid and automatic restoration after a power outage. However, PVs shut down in the case of a power outage and are not automatically restored. Therefore, it is necessary to compensate the electric power output of the PVs by using an extra power supply at the time of power recovery. For this compensation process, it is necessary to monitor the unmeasurable power outputs of the PVs, including those belonging to other organizations and individuals, to ensure that the automated operating system is used properly. Based on these aspects, in our previous work, a novel method was proposed to estimate the PV power output of an electrical power system using the measured power flow and solar radiation intensity. In this paper, we confirmed that the accuracy of the proposed method is sufficiently high using year-round data observed from The Kansai Electric Power Co., Inc., and characterized the relationship between the PV implementation rate and accuracy of the proposed method.
This study aims to quantitatively clarify the impact of large variable renewable energy (VRE) which is concentrated in some districts. Such districts will have difficulties to balance between power demand and supply, and keep the load frequency control (LFC) ability, and will be forced to curtail much VRE. Authors developed a simulation model to optimize generation mix and hourly operation of thermal and pumped hydro generation considering partial load efficiency, LFC supply and demand, and power transmission between districts. With this model, the authors obtained the following results on Japan's power system in 2030. (1) When VRE ratios to power system size are averaged, the VRE curtailment rates will much decrease. This way is difficult for wind power and other measures are required. (2) The curtailment rates can decrease a little by having some extra capacity of LNGCC though this is a very expensive way. (3) The capacity factors of LNGCC will be very low in some districts, and some incentives to hold LNGCC are required to use VRE stably.
Nowadays, Photovoltaic generation (PV) and all-electric house are well developed in distribution system which cause the unbalance of voltage and lead the power quality to get worse. Normally, unbalance of voltage is regulated by Static Capacitor (SC) or Static Var Compensator (SVC). However, PV which relies on the solar radiation that can't be accurate predicted varies a lot in short period and causes a reverse power flow, and the established devices come to inadequate with the feature of PV. To regulate the voltage and voltage unbalance factor (VUF) in PV connected distribution system, Battery Energy Storage System (BESS) is taken into using because it can give a fast, accurate, and flexible output, and its feature of absorbing the reverse power flow caused by PV is significant. However, the cost of BESS is relatively huge. To reduce the cost to propel the application of BESS, SC is here to combine with BESS to give reactive power output to decrease the capacity of BESS. The placement of BESS is discussed to give an excellent control as well as reduce the capacity of BESS. In this paper, a simply regulation of voltage magnitude is taken out to realize the improvement of VUF through comparatively accurate control of BESS with using the proved proportional relationship of the difference of line voltage and voltage unbalance factor (VUF).
High penetration of variable renewable energy (VRE) systems will impact power system operations because generation of VRE systems depends on weather conditions. We analyzed the operational situation and photovoltaic power yield curtailment for the Tokyo Electric Power Company area in 2030 using day-ahead unit commitment (UC) model when a high penetration of VRE systems is expected. At first, we updated our UC model to optimize PV curtailment keeping power system's security (load frequency control reserve) and minimizing operational cost. Using the updated model, we found that in case of 53GW and 100GW of PV penetration, around 0.34% and 4.83% of PV curtailment would be required throughout the year. High curtailment rate would be required only in spring and autumn seasons when power demand is small and PV yield is large. Regarding the other seasons, high curtailment rate would not be needed in any of the high PV penetration scenarios.
Recently, a large amount of photovoltaic generation systems (PVs) has been introduced in the distribution line. However, they may cause voltage fluctuation violently by changing the output of PVs due to variation of the weather conditions. To maintain the voltage of lines, Load Ratio control Transformer (LRT) and Step Voltage Regulator (SVR) are used in distribution network. However, as they have time delay to operate, they could not appropriately suppress violent voltage fluctuation caused by PV's output. Furthermore, frequent operation of LRT and SVR is also severe problem for their lifetime. In order to overcome those problems, the advanced control method of LRT and SVR is required instead of expensive devices, such as Static Var Compensator (SVC) and Battery Energy Storage System (BESS). From this background, this paper proposes the novel control method of LRT and SVR in consideration of the communication delay of the distribution automation system. The proposed method is variable dead band control using the estimated voltage profile correcting with the information from section switches. The proposed method is evaluated by the numerical simulation using the long line distribution model with two SVRs.
Various forecasting methods for photovoltaic (PV) generations have been proposed so far. However, the conventional methods cannot be widely used in various situations because they require sophisticated data that cannot easily be obtained. Furthermore, the prediction accuracy of such methods tend to deteriorate especially due to lack of data.
This paper proposes a simple and reliable PV forecasting method for local energy management. The proposed method uses only public weather forecasting data that is easily obtained. The method maintains high accuracy by using the real time correlation data between the target and neighboring areas. Multiple neural networks are effectively used based on a weather clustering technique. It has been confirmed that the proposed method shows the robustness in the prediction accuracy when used for local area PV prediction.
This paper describes a mechanism and its countermeasure of a hunting phenomenon caused by an anti-islanding scheme using a frequency feedback method of photovoltaic generation. It is known that the hunting phenomenon occurs when large PVs are connected to the end part of a long distributed transmission line, and it was observed in some experiments and simulations. But the hunting mechanism hasn't been clarified yet. The authors describe the hunting mechanism theoretically using a linearized model and a detailed model, and then check it by Nyquist plot and Y-ho simulation. The hunting is induced by a frequency positive feedback between power system and reactive power injected by the anti-islanding scheme. A simple and effective countermeasure is to add a first-order time delay to the signal of reactive power.