The article reviews present situation and recent technology trend of 4R (Recycle, Reuse, Reduce, Repair) in electric power wires and cables. Based on the result of questionnaires to electric power companies and buyer of removed electric wires and cables, the amount of removed electric wires and cables and present situation of 4R were investigated. Many conductors of removed wires and cables are recycled as conductors again, but plastic materials of them that recycled again as plastic materials of wires and cables is not enough. Therefore, in order to improve the ratio of recycling, application of the recycling material to products other than wires and cables is considered and the new technology for recycling into the material of wires and cables is studied.
The relationship of AC breakdown performance and water tree has been reported. This time, using aged XLPE cables with some protrusion on the outer semiconductor layer, we evaluated the relationship of water tree growth and impulse breakdown performance. As a result, in case of XLPE cables without waterproof layer, it was confirmed that the impulse breakdown performance decreased because of water tree, and we got possibility the impulse breakdown performance depended on the progress of water tree growth. In addition, it might decrease to the around LIWV. On the other hand, in case of XLPE cables with waterproof layer, though water tree progressed slowly, the impulse breakdown performance was maintained for a long time. In other words, the effect of waterproof was proved. Even if XLPE cables with waterproof layer have big protrusion, most of water tree started from the protrusion does not grow up. But, if water tree grows up, it may largely reduce the impulse breakdown performance of XLPE cables with waterproof layer.
High-temperature superconducting (HTS) power cable has significant merits of compactness and large power transmission capacity. To evaluate its performance, safety and reliability, HTS cable system was constructed at Tokyo Electric Power Company's Asahi substation in Yokohama, and the HTS cable had been connected to a real grid from October 29, 2012 to December 25, 2013 for the first time in Japan. The in-grid operation had continued for more than one year without any accidental interruption of the operation or troubles of the system. It is concluded that the HTS cable system has good performance and stability for long term in-grid operation. This paper describes the result of the HTS cable demonstration and their characteristics.
One of the degradation diagnostic methods for water tree degradation of XLPE cables is the residual charge method. In this method, a DC voltage is applied to a water tree degraded XLPE cable in order to accumulate space charges in water tree parts of an XLPE cable, and an AC voltage is applied to it in order to release deeply trapped space charges, i.e. residual charges. The authors have been developing a new diagnostic method with pulse voltages instead of DC and AC voltages. In this study, we first applied pulse voltages with a pulse width of about 1ms to an artificial water tree degraded XLPE cable, and found that the residual charge increased with the increase in the degradation degree. Second, we confirmed that residual charges were successfully detected in the removed 6.6kV XLPE cables that had water tree degradation. Finally, we investigated the relationship between the residual charge signal and the AC breakdown voltage of the removed 6.6kV XLPE cables. The results clarified that the removed cables with larger residual charge and longer duration of current signal related to water tree degradation had a lower AC breakdown voltage.
In this study, we evaluated deterioration characteristics of XLPE insulation under higher electric field than threshold level using block model samples with needle-plane electrode and also XLPE cable model samples with simulated defect. We conducted long-term aging test more than 50000 hours and life exponent “n=18” was obtained from the constant life exponent of V-t characteristics (inverse power's law (V-n=t)) of XLPE block samples, and “16.8” was obtained from the constant life exponent of V-t characteristics of XLPE cable samples. Even when the defects existed, it was confirmed that the deterioration characteristics showed the life exponent to be close to the conventional design value of “n”=15. We confirmed that with regard to the oxidative ageing behavior, the electric field dependency was observed in the defect by needle electrode, in which higher electric field shows higher ageing especially. It is suggested that the deterioration characteristics is gradually influenced by oxidative ageing with time and accelerated by related electric field.
High voltage direct current (HVDC) systems are generally superior to AC systems in case of long distance transmission, because of efficiency, total cost and so on. In recent years, the demand for HVDC transmission systems has been rapidly increasing for grid interconnection, power supply to island and export from offshore wind farm. Nowadays, extruded cables are preferred due to their advantage in load capacity, impact to environment and maintenance. The special insulation material which has excellent performance of resistivity and space charge for DC application had been developed. HVDC XLPE cables using that material and their accessories had been tested in accordance with CIGRE TB-496 up to 320kV. All of those developments were satisfactorily completed.
This paper investigates the influence of MPPT control method in the PCS on the occurrence of reverse voltage in PV modules. When the power of modules in part of a PV array declines, a situation arises in which those modules must be replaced with modules of different rated value. In such a case, the difference in the characteristics of existing modules and replacement modules may cause the occurrence of reverse voltage by MPPT control of the PCS in the replacement modules, which may cause heat and ignition. Although protection devices are connected to protect the modules from the occurrence of reverse voltage, they may not work. Therefore, it is indispensable to clarify the range of safe combinations of modules of different rated value. First, an MPPT control algorithm of three kinds of PCSs is implemented. To validate the developed control algorithm the simulated operating voltage is compared with measured one. Second, in order to clarify the conditions under which reverse voltage is likely to occur, the influence of the MPPT operation, open circuit voltage and short circuit current of PV modules and the pattern of connection of existing and replacement modules in a PV array on the occurrence of reverse voltage is investigated.
In this paper, the authors propose an electric power interchange system in collective housing with fuel cells (FCs) and a determination method of operation plan for FCs in the collective housing. In the method, the operation plan for FCs is determined from an evaluation point, primary energy consumption of all houses in the collective housing, based on an enumeration method and particle swarm optimization (PSO) which is one of non-liner optimization methods. In order to examine the validity of the determination method, numerical simulations are carried out for the collective housing model, primary energy consumptions of the model are compared to those of a standard system (without FCs), and the reduction effects are evaluated taking uncertainty into consideration by using 10,000 demand patterns which are represented by 40 observational demand data based on the bootstrap method. In addition, the reduction effects by reducing introduced FCs by half are also evaluated from the point of primary energy consumptions, operating efficiency and running efficiency.
This paper focuses on the effects of a control method utilizing MAS (multi-agent system) for a dc micro grid. The dc micro grid is composed of several PV (photovoltaic) generation systems and a centralized battery bank. The MAS is introduced to control the dc micro grid for a more flexible and stable operation. In this paper, two main control algorithms were proposed based on MAS. They are MPPT priority control algorithm in a group and power exchanging control method among groups. The MPPT priority control was proposed to take power from PV array as much as possible and reduce DC link voltage variation. The power exchanging control was proposed for flexible and stable operation of system by exchanging proper amount power for power shortage group. Those algorithms are implemented by TMS320F28335. 4 cases of experiments are conducted. 1. An experiment with a control based on local information without MAS in a group. 2. An experiment of a control with MAS in a group. 3. Comparison of generated power by controls with/without MAS in a group. 4. Power exchanging control based on MAS between groups. Those results are shown that the control algorithms are effective to control of dc micro grid.
To explore the possibility of implementation of demand response (DR) program for Japanese commercial buildings, we studied the load impact and customers' acceptance of demand responsive air-conditioning and lighting load control through a field test at two office buildings located in southern Tokyo Metropolitan area, which was conducted in summer and winter of FY2012. The summer experiment results show that, automated DR (ADR) control can shed the load demand during DR hours with some certainty but very likely decreases the subjective working efficiency of workers in the controlled floors. This implies that advanced ADR control techniques having little effect on working efficiency are needed to gain the customers' acceptance and improve the DR value. Pre-cooling might be a promising summer DR technique. The winter experiment results show that, ADR control sheds load with high uncertainty and further research is needed to develop winter DR techniques.
The topology optimizations which optimize a material arrangement on an element, without extracting feature quantity, are attractive methods, because we can obtain a free idea of the initial design of magnetic devices. However, in actual design processes, all of the required features of the products cannot be included objective functions, such as ease of manufacture or influence of rise in heat. Moreover, the multiple-purpose optimizations concerning many kinds of physical phenomena have difficulty with calculation time. Thus, it is necessary to estimate whether the obtained optimal solution under the limited condition is applicable to an actual designing of magnetic devices. This paper introduces two-step topology optimization method using the constraints on the similarity of the topology, which provides us various topologies including suboptimal solutions. By using the proposed method, we can determine some actual applicable solutions out of obtained solutions. The proposed method was verified by applying it to the C-core problem and the magnetic shield problem, which demonstrated the effectiveness of the proposed method.
In recent years, residential solar power systems have been increasingly introduced at a rapid pace. To date, lightning surge currents have been considered to intrude into houses via four kinds of routes, power lines, communication wires, antenna wires, and ground wires respectively. However, if a residential solar power system is installed in a house, an additional lightning surge current will eventually come from the residential solar power system. On the other hand, it is thought likely that more electronic watt-hour meters, or so-called smart meters, will be installed in future. Since electronic watt-hour meters may potentially be more vulnerable to lightning compared to conventional mechanical watt-hour meters, more attention must be paid to the influence of lightning on electronic watt-hour meters. In this paper, lightning impulse tests were conducted for houses where a solar power system was installed. To study the influence of lightning on an electronic watt-hour meter, it is crucial to clarify the condition of the lightning surge current flowing from a residential solar power system hit by a lightning stroke. During these tests, the propagation condition of the lightning surge current flowing from the residential solar power system through the distribution line and the watt-hour meter was studied.
The 2011 off the Pacific coast of Tohoku Earthquake was a massive earthquake of magnitude of 9.0 occurred 11 March, and was long duration time. Though the electrical accident had been widely occurred in the Kanto region, the cause of occurrence was not easily understood concerning the short-circuit accident between transmission lines. In this paper, after understanding the fact of the event, simulation model of occurrence site was made and the event reproduction analyses were done to clarify the possibility of the event reproduction. In addition, the cause of the short-circuit was considered by using a seismic design standard related to gas piping targeting the Rayleigh wave and the long-period earthquake ground motion prediction map while thinking about countermeasures to short-circuit accident in the future.
Deterioration diagnosis of a lead acid battery by phase change between impedance and reactance was measured. The measurement frequency of inner impedance was changed from 100Hz to 5kHz. The lead acid battery with 11V open terminal voltage at the charge condition of 60% was judged as enabled in case the phase of impedance was more than 35 degrees when the application limit is CCA 180 Ampere.