Real systems inevitably include some kind of nonlinearities. Power system is a typical nonlinear system with a huge scale. The steady state stability and the transient stability of power systems result from the intrinsic nonlinearities. Bifurcation theory tells us various kinds of nonlinear structure. In this article periodic orbits and chaotic behaviors detected from the view point of nonlinear system analysis are explained. Some engineering applications are also described.
FRIENDS (Flexible, Reliable and Intelligent ENergy Delivery System) is a new concept for a future energy delivery system. FRIENDS is characterized by the Quality Control Center (QCC) with dispersed generator and/or storage system in order to improve the system reliability.In this paper, the social cost is assumed as the sum of the rate of electricity, interruption cost and QCC cost, the effect of the QCC on area economy improvement is evaluated through the Monte Carlo Simulation. It is illustrated that the area economy may be improved by the QCC with reliability improvement, depending on the reliability level.
Recently many electric installations of consumers have been constantly energized. Therefore, the insulation of house wiring is diagnosed by measuring the earth leakage current with a clamp-type current transformer (CT) at the power-source earth line.In this situation there is a technical problem that the earth leakage current measured may include, in addition to active current due to resistances of installations and house wiring to the earth, reactive current due to the capacitance of house wiring to the earth. The authors developed a clamp-type CT equipped with a simple gadget that could remove reactive current(within 4.5mA) component, this provides accurate measurement of the minute active current (beyond 0.01mA). The feature of this instrument is that its measuring technique is based on an algorithm named as hyperbolic measurement method that is capable of arithmetic operation using only scalar quantity when the bias current is made to flow on the CT. As a bias current, a constant current (Ib) in phase with the source voltage and an antiphase constant current (-Ib) are superimposed on CT, respectively, in the first and second computation stages. The scalar values of the resultant currents are used in the computations. This paper describes how to remove electromagnetic noises from the outside as well as the basic theory of the technology developed, composition of an experimentally manufactured instrument, and its performance test results.
We investigated propagation properties of Lamb waves in GIS tank using time-frequency analysis to diagnose insulation performance of GIS. We measured the acoustic signals excited by a metallic particle colliding with the tank sheath, and those emitted by partial discharge in GIS as well. The Wavelet Transform was applied to decompose the wave data into its timefrequency components. As the result, it was confirmed that Lamb waves with the dispersive property of the velocity are excited and the waves propagate spirally along the tank wall due to the cylindrical structure of the tank. Taking these results into consideration, we proposed a new technique for identification of the defect location in GIS based on the time-frequency analysis of the acoustic waves using the Wavelet Transform.
Abstract Dissolved gas analysis in insulating oil is widely put to use as an important diagnosing method in the maintenance of oil immersed equipment such as transformers. The headspace method which is described in this paper is a method for extracting gases by heating and shaking a vial. It makes use of such a principle that the constituent concentration of the liquid phase portion and gas phase portion in the vial is dependent on the Ostwald coefficient. The authors paid attention to the rationality of the headspace method several years ago, and have been studying application of this method plus the prospect of putting in into practical use. Below are the results of the development and study in this paper; 1. Being constituted as a gas analysis system, it is possible to perform the analysis at a high sensitivity and precision. 2. Gas analysis can be performed with a sample of a small volume. 3. The analysis time is short and it is possible to continuously analyze up to 44 samples.
For a rationalization of insulation design of 22kV cable system, we had calculated transient overvoltages by EMTP. From the result of our investigation on actual conditions of the existing 22kV distribution line, some typical models for the calculation were selected. As a result of parameter analysis by the typical model, we determined the system condition of distribution line that caused the largest transient overvoltage. In the case of switching surge, there is little relationship between neutral resistance and the overvoltage, and then the maximum per unit value of abnormal voltage is approximately 2pu. On the other side, in the case of fault surge, the overvoltage increases as the neutral resistance increases, and then the maximum per unit value of the abnormal voltage becomes 2.68pu. According to the above results, the conventional test voltage for 22kV distribution equipments could be reduced by approximately 20%.
In this paper, it is made clear a detailed characteristic of a T type and a π type equivalent circuit of the two winding transformer. And a way of thinking of the π type equivalent circuit that can be applied in multi-winding transformer more than two windings is derived. Furthermore, concrete problems of a T type equivalent circuit are shown, and the derivation method of a practical use equivalent circuit to analyze a magnetizing inrush phenomenon of two winding transformers is shown.
We examined the possibility of the practical use of a conduction cooled magnetic shield type fault current limiter. A small superconducting fault current limiter was built and the current limiting characteristics were tested. The conceptual design of the conduction cooled fault current limiter for a distribution power system was carried out, and we calculated and discussed the temperature rise of shielding coil during a normal and a fault condition. We suggests the protection method for the quench due to local disturbance during a normal operation.
An 11.4-kV three-phase four-wire distribution system is capable of economically enhancing the supply power by using most of the existing 6.6-kV distribution system facilities. In this paper, the authors made a study on securing safety and quality in the 11.4-kV system by presupposing the use of a single resistance grounded neutral system based on EMTP simulations. For the safety aspect, we conducted a study on the application to the 11.4-kV system regarding the OCR and the DGR. As a result, the conditions for the application to the 11.4-kV system were revealed, such as setting up a switch with an overcurrent relay on the distribution line as a measure for extending the OCR protected zone, and the most optimum neutral grounding resistance value for secure earth-fault protection. For the electric power quality aspect, we propose the load connection phase control method and the Y-A wiring for the transformers for motors as measures for controlling the voltage unbalance. Through these measures it becomes possible to secure the quality similar to that of the existing 6.6-kV system. It is concluded that the basic technology has been established for a practical application regarding the protection scheme and the measures for keeping the voltage balance.
A governor control system for hydro power plant is newly developed. The main feature of the governor is to reduce water levelrising of the surge chambers even when load shedding or urgent start up occurs, and to improve load set point tracking ability. The governor controls the guide vane in such manners that it opens the guide vane when upper surge chamber water level rises so that the water level oscillation damps gradually. The control algorithm for the governor is designed applying LQG control method. Furthermore, the water level which is difficult to measure continuously is estimated by the software sensor by the pressure and power signal that are easier to measure. The system is examined by simulations firstly and proved its performances by the experimental setups.
This paper describes insulation diagnosis of SF6 gas insulated switchgears (GIS) by detecting partial discharge (PD)-induced electromagnetic (EM) waves using UHF method. Sensitively detecting PD signals is effective to prevent breakdown in GIS because PD is a pre-breakdown phenomenon. Breakdown in SF6 gas under nonuniform field takes place when PD type proceeds from streamer to leader discharge. Therefore, breakdown prediction becomes possible by discriminating PD type, that is, by detecting generation of leader discharge. An amplitude of PD-induced EM wave depends on the time derivative of PD current. Experimental results revealed that the time derivative in rising part of PD current for streamer discharge is almost same as that for leader one while that in the falling part is quite different. Thus, one can recognize the generation of leader discharge by noting the ratio of the EM wave magnitude of the positive peak value to the negative one of the first incoming EM wave. In this study, an attempt was made to discriminate leader and streamer-type discharges on the basis of the amplitude ratio of first incoming EM wave measured with UHF sensors. Furthermore, we investigated effects of trigger level of a digital oscilloscope in the measurement of the EM wave and UHF sensor position on detection sensitivity and discrimination probability of PD type while changing the SF6 gas pressure and the applied ac voltage. As a result, it was found that leader discharge can be discriminated from streamer one with a probability as high as 70% using a criterion of amplitude ratio of first incoming EM wave VP+/VP-=0.7. When VP-=0.8 is used as criterion, the discrimination probability increases as high as 80%.