To analyze multi faults on a power line, we need to perform many complexed calculations. So, in many cases, we used to do them, using computers, in the actual phase domain. But it is difficult to expose the property and/or the physical meaning of the calculated results, because the computer method is based on many complexed numerical calculations. This paper represents a new analytical method for short circuit studies, which can deal with crosscountry multi fault in double-circuit transmission line with zero-sequence mutual coupling. This method is based on the well known “two-component network theory” for a balanced three phase double-circuit. Procedure steps are; (1) Represent the network seen from the faulted points, with symmetrical component impedance. (2) Construct the symmetrical equivalent circuits for faults, with imaginary phase shifting transformers. (3) Combine these equivalents with each other, and erase the symmetrical voltages at faulted points, because the phase voltages at faulted points are known. (4) Calculate the currents at the faulted points, by solving the simultaneous linear equations. We applied this method to an investigation of a distance relay's “ underreach” phenomena in case of cross-country multi fault occured on a double-circuit transmission line. Effects of line constants to this phenomena have been well understood.
In an electric utility, it would be necessary to predict and make a future view of electric energy strategy for long-term generation expansion planning. The planning problem of energy strategy is formulated as a decision problem of electric generation system in a future horizon year. This problem is considered to be a sort of multiobjective planning problems under several constraints of which some parameters are uncertain. The objectives and some constraints are not necessary to be fulfilled perfectly, but some tolerances by a decision-maker's will may be allowed to them. That is, they can be regarded as fuzzy objectives and fuzzy constraints. This paper presents the fuzzy decision analysis of strategic generation system planning problems using a fuzzy linear programming technique and some numerical examples for a future power system are demonstrated.
Real time analogue simulator is useful for analysis of power system phenomena and for performance test of controller and protection equipment in power system. Large scale simulator and high precision simulator have been developed in recent years. Authors have developed two models which are required to realize a high precision simulator. One is a new circuit breaker model with loss compensation circuit that contributes loss suppresion in the simulator circuit. The other is an induction machine model which makes load characteristics closer to one in actual power systems. The induction machine model is a newly designed voltage output type and operates in stable that is composed by analogue circuit.
Shunt reactors installed at GIS-substations are switched relatively frequently by large capacity gas circuit breakers (GCB's). Surge voltages appear at such switching operations through various mechanisms. Among them, high frequency current interruption and subsequent multiple reignition might cause highest overvoltage and may be harmful to the insulation of the components of the substation. In this paper, shunt reactor current interrupting tests are conducted in high power laboratory. Existence of critical arcing time above which reignitions never occur is shown through these tests. From this fact, phase-angle-controlled-interruption system is proposed. With this system, arcing time is artificially set so that reignitions should be prevented. Reliability of this system is confirmed through reactor current interrupting test in the laboratory as well. After that, phase-angle-controlled-interruption system is applied to the shunt reactor switching at actual 275kV substation. Switching performance of this system is measured over three months. Reignition-free interruption is shown to be attained with this system.
Forced flow cooled superconducting coil (FCC) has several advantages of large stability margin, high mechanical rigidity and good electrical insulation. Having these merits, FCC could provide efficient superconducting magnet systems for large machines, such as fusion devices. Cable-in-conduit conductor (CICC) is regarded as one of the most attractive ones for FCC, because CICC has good heat transfer characteristics, which makes the magnet more stable against disturbances. There are some problems, however. One of them is that the coolant pressure will become very high during a quench, because its hydraulic diameter is relatively small. Besides, the propagation of normal zone has the close relation with the pressure rise. We must consider these characteristics to design and protect FCC. This paper describes the results of the stability tests of FCC and the analyses of these characteristics, and also compares them with the results of numerical simulations.
In order to keep the performance of pulsed power source consisting of many capacitors, switches connected in parallel with the load must be operated as nearly simultaneously as possible (the low distribution time). Monitoring the starting condition of each switches makes it easy to find and repair the malfunctioned switches. As a result, the reliability of bank system is expected to be fairly improved. A switch monitor system which has the above functions is developed and installed to the plasma experimental device TPE-2. The system consists of 312 channels of signal detector sections, a display section and a data acquision and processing section. The distribution of switching time (jitter) can be checked with a sensitivity of 100 ns which is necessary for the reappearance of power system. Signals from the detectors to the display section and GP-IB communication between the display section and the data processing section are optically connected to diminish electromagnetic noise. The reliability of power supply system of TPE-2 is significantly improved by use of the monitor system.
For the stable and high performance operation of the methanol fuel cells, it is essential to maintain water balance on the cathode successfully due to control of air flow rate. Generally, ion exchange membrane and sulfuric acid are normally used as electrolyte of fuel cells. Then, it was found that the increase of air flow rate was necessary to maintain water balance on the cathode successfully when high molecular polymer electrolyte was used and sulfuric acid concentration in anolyte was lowered. Therefore, this paper studied the consumption rate of methanol and water on the anode in case of with and without sulfuric acid, as parameters of current density, air flow rate, cell temperature and methanol concentration. As a result of the experiment, following things were cleared, (1) In the relation to air flow rate, water permeated into the cathode through the electrolyte layer from the anode in case of water shortage in the cathode. (2) The water permeability rate in case of without sulfuric acid became 2.8 times greater than that of with sulfuric acid.
The solar radiation has an irregularly varying factor due to a basic day and night cycle and climatic conditions. For such conditions a data sampling interval is important to assure the accuracy of energy monitoring in photovoltaic system. While treating a system monitoring equipment as a black box, the author has developed the method of calibrating an energy integrating function. At first for various input waveforms have been examined the relationship between sampling intervals and quasi integration outputs by trapezoidal rule. In the numerical simulation the phases of sampling clock are also considered. After all it is concluded that a sampling interval can be inspected through outside observation only by using a rectangular single pulse. By applying the pulse to the energy integrating process, two kinds of integrated outputs can be obtained for different sampling phases. The calculated difference between the both outputs can uniquely give sampling interval being inspected. Conditions to assure measuring accuracy are discussed and the validity of this method has been demonstrated experimentally. practical calibrating procedures are also proposed for the integrating function of PV system monitoring.