Power capacitors have contributed greatly to the effective use of electric power, such as network voltage adjustment, line loss reduction and power factor correction. And harmonic filters have contributed greatly to the power quality improvement. Then, by the ripe capacitor application technology and the development of power electronics, they have evolved into such static var compensators (SVC) and voltage dip compensators. In recent years, the fluctuation of voltage and frequency and the increase of harmonics, due to the rapid increase of renewable energy power such as PV and wind power have occurred, and additionally the over-lead power factor or the Ferranti effect due to increase the use of inverter technology in load devices and energy saving have occurred. The countermeasure to these issues by the changes of sources and loads in power systems has been requested for power capacitors and their applications. Considering these circumstances, in this commentary, while investigating the influence to power quality by the over-capacitor installation and by the change of power supply and load, and introducing the evolution and development by power capacitors and their applied technology, the left-behind subjects are described.
Constant power factor control of a power conditioning system in a large-scale photovoltaic generation system (PV system), such as a mega-solar system, is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the loss change on the distribution line. This paper proposes an advanced reactive power control, in which the power factor of the PV system is adjusted both by output power of the PV system and by apparent power of loads not to minimize the voltage variation at the interconnecting point but to minimize the voltage variation over the whole distribution line, and reports the result examined by numerical analysis about mitigating the voltage variation by applying the control. This paper shows that the proposed control can mitigate the voltage variation more than constant power factor control and there is a probability that it will be applied as a measure of suppressing the voltage variation on the long distribution line.
Installation of renewable energy sources in island grids is focused on as large expense of island power generation and their power fluctuations should be conpensated. Desalination system is being focused on as a controllable load. This paper proposes a model for the desalination system, estimates controllable ranges under restrictions and evaluates the ability to suppress the power fluctuations. The model calculates the pressure, flow and power consumption. Parameters of the model are fitted by tests with an experimental system. Next, controllable ranges of power consumption under restrictions of the membrane etc. are estimated both by tests and by the model. Controllable ranges with fixed valve openness are estimated as 27 to 43 percent of its rated power. Finally, to evaluate transient response, step and ramp response tests and photovoltaic (PV) output suppression tests are conducted. Most of the fluctuations of PV output are suppressed when PV output is within the controllable range.
In order to address climate change and energy security issues, intermittent renewable energy sources, such as solar photovoltaic (PV) and wind power, are gaining great attentions. However, due to their variability and surplus electricity, the expansion of these renewables is an important challenge for power grid management. Various treatment measures, such as rechargeable battery, curtailment and back-up generator, are considered necessary for the physical integration of intermittent renewables to construct efficient and reliable power generation mix. In this context, the authors employ a high time-resolution optimal power generation mix model to quantitatively assess the amount of surplus electricity under massive introduction of PV and wind power in Hokkaido region of Japan and potential roles of the treatment measures mentioned above. The main feature of the model is detailed time-resolution, 10-min through a year, which allows us to investigate impact of various short-cycle renewable variations on surplus electricity and deployment of rechargeable battery. Simulation results potentially suggest that if fraction of PV and wind power expands more than around 10% and 20% of total demand respectively or if sum of PV and wind power fraction exceeds 20%, need for curtailment grows rapidly. The results also suggest that rechargeable battery has better economical compatibility with PV rather than wind power.
The rate of renewable energy will increase to 40% by 2030 in Maui Island. It will be challenge to keep electric frequency when wind generation reduces suddenly. In late years, electric company in Hawaii controls residential water heaters to keep electric frequency. But the comfort impact for consumers by demand control is very large. So we propose the new demand response method “Emergency DLC Algorism” to improve comfort impact for consumers. The characteristics of our Emergency DLC algorism is multistep control request. It can reduce the over load control from target value, can complete load control before the dead line and can reduce the comfort impact for consumers.
Transmission and distribution (T&D) systems for electric power are assembled with a large amount of aged apparatus, the deterioration of which may cause a decrease in reliability. In order to maintain high efficiency and high quality in T&D systems, it is important to minimize both present performance costs and future performance costs. Typical present performance costs are T&D losses, and typical future performance costs are failure losses and apparatus maintenance for overall T&D system optimization. We have to consider concurrently two concepts that are an asset management system and a smart grid. This integrated concept, which we have proposed as Intelligent Grid Management System (IGMS), achieves optimum control that includes the present power flow and the future maintenance of the T&D system. In this paper, the effect of temperature rises in transformer windings is formulated and integrated into an objective function to determine transformers with power flow control. The derived power flow control optimizes the load sharing of each transformer by keeping a balance between the T&D loss and degradation in the transformers. The degradation of aged transformers is prevented by reducing their load factor, or the aged transformer is replaced with a new one that accepts a relatively high load factor.
Ground fault location in distribution line is specified the restricted area by sequential fault detection system. Then, ground fault location is identified by detecting magnetic field originated discharge current from direct pulse device on electric pole. It needs much time to identify ground fault location due to involving works on electric pole. Recently, introducing switch with built-in sensor (ITSW) is considered on the purpose of efficient operation against amount of diffusion of Photovoltaic Power Generation Systems Source. For the purpose of introducing IT switch, ground fault location detecting method is studied by IT switch. As one of the means, it is studied the shortening of ground fault location detecting hours. For example, ground fault location is identified by the difference in arrival time of ground faults surge current from different measuring points, classification of characteristics from wave form in ground fault current, and so on. In this paper, we propose that it is estimated the brunch point from the high frequency component by measuring the wave form of ground fault current in transient state of both feeding direction and terminal point, and is verified by ATP simulation to check the validity of proposed method. In addition, we study the improvement of proposed method precision.
This paper describes a methodology for designing a cost-efficient transmission system configuration on a green field where we consider land condition, generator condition, load condition, and acceptable reliability. The reliability constraints include static constraints under normal and N-1 conditions, and transient stability constraint for three-line-to-ground faults. Under the N-1 condition, power generation rescheduling is considered to obtain a solution at lower cost. The proposed method divides the design problem into two stages. The size of the problem is reduced by applying Dijkstra's algorithm in a preparatory stage, and then, the problem is solved by a PSO-based algorithm in an optimization stage because we have to deal with integer variables and differential equations. The proposed algorithm is tested for a small green field with three generators and three loads, and the results show impacts of the generation rescheduling and the transient stability constraint on the designed system configuration. Finally, we verify the effectiveness of the proposed method for a larger green field modeled based on north-east Japan system, and show that the algorithm can solve the problem with a reasonable cost-effective solution.
A remarkable characteristic of a vacuum arc cathode spot, which can remove an oxide layer, is that it moves across the metal surface. However, the contribution to the moving mode of the vacuum arc cathode spot remains unclear. This study elucidated the contribution to moving mode of the vacuum arc cathode spot as affected by the oxide layer thickness. Experiments were conducted using an SS400 cathode and a cylindrical copper anode. A high-speed video camera recorded the cathode spot movement with ND (Neutral Density) and a band pass filter. The obtained images were then analyzed using plasma image processing. The cathode spots have four moving modes: oxide layer removal, split, stagnation at the boundary between the oxide layer and the processed surface, and high-speed movement on the processed surface. Oxide layer thickness affects the cathode spot moving mode because of the maintenance of the current continuity of the cathode spot with oxide layer vaporization and ionization. Oxide layer thickness affects the cathode spot movement.
The improvement of power performance for a polymer electrolyte fuel cell by microwave processing was shown in this report. We attempted to determine the cause of these performance enhancements by performing a fixed-quantity mapping analysis with a scanning-type microscope. This study was conducted to develop a novel method to form minute holes to raise the oxygen permeability and drain ability for this ionomer.