With ensuring the public safety, reliability and economic efficiency, insulated electric wires, cables and their accessories used in distribution lines have been improved to fit to their usage environment. This article briefly describes their technical transitions, especially for the upgrades in their functions as well as structures. Some current technical issues are also given in relation to new demands emerged the changes in social situations.
At the time of the commissioning of an underground cable transmission line, it is a common practice to perform measurement of its electrical constants. In such measurement performed by a cable manufacturer, the following straightforward method is used for each circuit of the cable line. A three-phase voltage source is used to apply a balanced three-phase voltage at the power frequency to one end of the cable circuit with the other end short-circuited, and the positive-sequence impedance is obtained by the measured voltage and current. To obtain the zero-sequence impedance, a single-phase voltage at the power frequency is applied to the bonded three-phases of one end of the cable circuit, to the ground, with all phases at the other end grounded. If there is no parallel cable circuit in service, this method gives an accurate result. However, if there are one or more parallel cable circuits in service, the cable circuit under measurement gets electromagnetic induction from the magnetic flux generated by the currents on the parallel circuits. This induction generates superimposed currents and thus makes the measured result inaccurate. Considering this point, a method to measure a voltage and a current at a frequency different from the power frequency so as to separate the power-frequency current component generated by the electromagnetic induction and obtain the impedance value at that frequency is proposed in this paper. Using impedance values measured at two frequencies different from the power frequency, the power-frequency impedance value is then obtained by linear approximation. The proposed method is applied to obtain the impedances of a 132-kV underground cable line, and a reasonable result is obtained.
Load flow calculation is the fundamental analysis in electric power systems, and most of the load flow programs use well known Newton-Rapson (NR) method. The NR load flow programs normally converge within several iteration to the solution. However, nonconvergence within the specified number of iterations often occur, mainly caused by infeasible data. A lot of try and error effort will be needed to obtain the converged solution for it.
In this paper, a load flow solution method for infeasible conditions is proposed. The proposed method firstly judges whether the data is feasible or not in the iteration process, by using voltage stability index of each load node. For the infeasible case, appropriate load shedding will be taken to obtain the load flow convergence. The node of load shedding indicates the weak aria in the network from the viewpoint of the load flow convergence. The information can help the users to focus the modification or correction of the data, and to obtain the convergence easily.
The demonstrative application to both Kros & Kerner 11 node model and IEEE 118 node model are presented in order to verify the practicability of the proposed method.
We propose the islanding detection method by estimating the changes in the second harmonic impedance before and after islanding operation. As the active signal, the second harmonic current is used. By detecting the ratio of the secondary conductance, it is possible to restrain the decline in detection sensitivity even for a load with a large quality factor or in multiple connection with inverters that have different islanding detection method. We have developed three single-phase inverters for low voltage interconnection and clarified the effectiveness of the proposed method.
The circuit breaker is required to interrupt the current in order to prevent the spreading fault current. The re-ignition caused by remaining the high temperature gas in the opening of circuit breaker occurs. As this countermeasure, the external magnetic field application and blast gas to arc are used in order to decrease the arc temperature. It has been reported that the non-thermal equilibrium of arc is remarkable near the electrode and post arc. However, few reports have the analysis of separating electron and heavy particle momentums under consideration of the non-thermal equilibrium because the physical phenomena are complicated in the non-thermal equilibrium. In this paper, the electron and heavy particle velocity distribution under consideration of non-thermal equilibrium arc was analyzed. As a result, it is possible to quantify the electron and heavy particle velocity. The electron velocity distribution is dominant to the electric potential distribution. On the other hand, the heavy particle velocity distribution is dominant to the pressure gradient. Therefore, the difference between the electron and heavy particle velocity distribution was elucidated.
The purpose of this paper is to establish the designing scheme of simplified structure of superconducting coils for particle beam accelerators, which can be easily manufactured, by using of the procedure of topology optimization. We set three axes of design requirements for particle accelerators; magnetic field homogeneity, magnetic field strength and cross sectional area of the coil. We formulated the objective functional and developed the optimization algorithm to solve the multi-objective problem. In the algorithm, we applied the Heaviside-projection method to avoid gray-scales and excessively complex structures. Finally, the validity of the proposed scheme was confirmed with numerical examples of coil designs.
This paper presents the development results of surge absorber system for an ITER neutral beam injector. Circuit design and insulation design were carried out to withstand 200 times breakdown at beam source. Circuit analysis considering the B-H characteristics of FINEMET core for surge absorption shows the decrease in surge current by 60% due to the developed system. The validity of the established design was demonstrated by the actual-product tests for Transmission Line 2; FINEMET core satisfied the required saturation characteristics of 0.7Vs, and also withstood the impulse voltage of 200kV loaded in the axial direction at the reduced pressure condition of 0.1MPa,abs in the SF6 gas atmosphere.
In this study we present the results of an experiment regarding the process of exposure and concealment of PV, photovoltaic, module interconnect failure, induced by temperature change. To carry out the experiment we built a PV string of modules with interconnect failures and observed its I-V characteristics for six months. Each PV module had two clusters, and each cluster had its cell strings output electrodes connected to a bypass circuit with diodes. The experiment showed that when the module temperature increased, the open circuit voltage and maximum power voltage of the PV string decreased below the amount indicated by the temperature coefficient. However, once the modules temperature decreased both voltage values returned to their original values. Regarding the dependence of maximum power voltage on temperature, we observed that it varies linearly in discrete intervals of voltage, and that such intervals were in agreement with the output voltage variation of the PV clusters. Moreover, the number of discrete intervals correctly indicated that eight PV clusters had interconnect failures, and at 60°C between seven to eight interconnect failures could be identified. However, when the temperature of the modules dropped to 25°C at most 2 interconnect failures were detected, indicating the occurrence of a concealment process. Finally, the study also shows the usefulness of the bleeder resistance method, and of the constant current method to detect interconnect failure in outdoor conditions.
A hybrid DC switch has been studied extensively due to the increasing demand for photovoltaic plants or DC power distribution systems. The advantages of the hybrid DC switch are low contact resistance and high-speed interruption. We have demonstrated an arc-less commutation of current from copper-based tungsten contacts to a SiC-MOSFET. The arc-less commutation prevents the contact erosion that is one of the drawbacks of conventional DC mechanical switches. This report shows the experiment results on the threshold current of the arc-less commutation and the contact resistance with different material contacts up to 400A in a Hybrid DC switch.