This article surveys the latest aspect of metal-oxide surge arrester technology in overseas with regard to evaluation of the performance and application issues. The IEC standards for surge arresters are mainly reviewed, in comparison with the JEC and IEEE standards. Through the investigation several points to consider on testing standards and application guide are addressed.
Photovoltaic (PV) power generation systems have gained much attention against a background of energy and environmental problems. However, the output of PV system depends on climate conditions. Therefore, a mass introduction of PV results in the power quality deterioration in the distribution system. To overcome the difficulty, it is effective to introduce Low Voltage Regulator (LVR) to the distribution system. However, the application of LVR brings a new problem, i.e., a control delay for activating the tap after detecting the fluctuation. With this background, to provide more useful predictive information in advance, this paper deals with a novel prediction interval estimation method of 10 second PV fluctuation with two-dimensional kernel density estimation. We also carry out the prediction by using several different methods for comparison, e.g., the conventional method with one-dimensional kernel density estimation and the application of various smoothing methods to this conventional method. Finally, some numerical results, which demonstrate the effectiveness of the proposed method on the basis of several indexes, are also presented.
This paper proposes a new method for distributed voltage control, which is effective on system re-configuration and improper motion of voltage control devices for distribution networks. The authors have so far proposed a distributed voltage control method for distribution networks by means of multi-agent framework, which is an optimal control both for minimizing tap changes and voltage deviations. In this paper, several effective ideas and functions are introduced to the proposed method to enhance the performance. The re-configuration is executed by management of system data using the management agent and blackboard memory and the improper motion is prevented by providing a new index to the agent. The effectiveness of the proposed scheme is demonstrated through numerical simulations with successful results.
This paper describes rising and reducing processes of receiving-end voltage due to a reverse power flow from large photovoltaic generation in distribution electric power system. The dependences of the voltage increase and decrease on the length of distribution line are discussed with consideration of vector (phasor) diagram of voltage and current. Furthermore, the effect of leading power factor control of the PV system on the distribution line voltage is also quantitatively revealed.
A pulse-assisted ionization discharge applied to a magnetohydrodynamic (MHD) generator is proposed as a technique to increase an electrical conductivity of working fluid. In this study, a periodic structure of output power in the MHD generator by using pulse-assisted ionization discharge was evaluated. As a result, the discharge electrode length and the velocity of working fluid affect the discharge current distribution. The periodic structure of output power was observed in the several conditions. When the velocity of working fluid is roughly same as the sound speed, the periodic structure of output power was not observed.
Mass productions of the motor core such as the blanking of the electromagnetic steel sheet and the shrink fit cause the residual strain in the material, processing strain, which prevents the movement of magnetic walls and increases the magnetic loss in the motor. Conventionally, the increase of the magnetic loss by the processing stress was evaluated with trial products, because it couldn't be done in the design phase. Particularly, the residual stress generated by processing has a complicated relationship with the direction of the magnetization vector, which has made it difficult to estimate iron loss considering processing strain.
So this paper clarified the relationship between the stress tensor and the magnetization vector, and proposed a consideration method of the stress in magnetic field analysis. As a result of validating the development method with the ring test piece, we confirmed that the intended modeling can be reproduced. Furthermore, we showed the usefulness of the development method in the motor model.
As a solar cell connected in series in a solar module fails, the operating module current decreases, however the operating voltage of each cell is not measurable if the cells are sealed tightly in the module. This research proposes a method to estimate an operating cell voltage in a module by irradiating modulated light to the cell and detecting the modulated signal from a load resistance of the module by a phase detector. And experiments for a small scale module to confirm the method have showed that the modulated signal detected by the phase detector increases as an operating cell voltage decreases, as expected according to the proposed theory. Therefore, it is confirmed in principle that the proposed method can estimate an operating cell voltage in a module.
For the demonstration of feasibility and loss-reduction effect of the larger-capacity amorphous core transformers (AMT), this paper proposed the support structure and design method of the iron-loss reduced amorphous wound cores with a weight of 7 tons. We designed and manufactured 10 MVA single-phase test model with the cores inserted in a support cage having structures of the stress-buffered core support, the proof electromagnetic force from the windings, and the stray loss-reducing shields. The 50%-loaded total loss of the test model estimated from the calculated and measured results has been reduced by 35% compared with a conventional silicon-steel core transformer (SST) with the same power capacity.