The increasing use of highly sensitive electronic devices is starting to draw the attention of consumers to the issue of voltage sags. This article presents the current status of voltage sag mitigation devices.
This paper describes interfacing techniques for connecting fully digital and analog real time simulators. Three types of interfacing techniques, which are applicable for long transmission lines, short transmission lines, and transformers, are developed and tested. Further, these interfacing techniques are validated through detailed simulation studies carried out by actually connecting a fully digital real-time simulator (HYPERSIM) and an analog simulator (PSA). The interfacing technique using a transformer is shown to be quite promising for practical applications.
This paper proposes a multi-agent approach to maintenance scheduling in restructured power systems. The restructuring of electric power industry has resulted in market-based approaches for unbundling a multitude of service provided by self-interested entities such as power generating companies (GENCOs), transmission providers (TRANSCOs) and distribution companies (DISCOs). The Independent System Operator (ISO) is responsible for the security of the system operation. The schedule submitted to ISO by GENCOs and TRANSCOs should satisfy security and reliability constraints. The proposed method consists of several GENCO Agents (GAGs), TARNSCO Agents (TAGs) and a ISO Agent(IAG). The IAG’s role in maintenance scheduling is limited to ensuring that the submitted schedules do not cause transmission congestion or endanger the system reliability. From the simulation results, it can be seen the proposed multi-agent approach could coordinate between generation and transmission maintenance schedules.
We proposed the technology which estimates an electric current value at the time each being positive for each power distribution line. Generally, as for the reported demand forecast (for example, are demand forecast by the electricity supply place level and so on), to consider that the load which becomes a base moves isn’t necessary. However, as for the power distribution system, the change of the composition which is due to the system changing, and so on, and the load curve shape, too, have changed mainly. So, the section of the power distribution line was classified in four kinds of clusters by the composition ratio of every contract classification, and created in the estimate model by the multiple regression analysis. Furthermore, to improve the precision of the estimate model, we calculated an error coefficient of each power distribution line and established the error revision method which distributes an error coefficient to each section. As a result, the absolute average error with estimate electric current value by this technique was 7.7A and it was possible to confirm that 95% was stored within 30A. This paper describes a method and validity of the load forecasting technology in the power distribution system.
This paper describes the effect of mutual leakage reactance in rotor circuit on analysis of generator transient characteristics. The authors derived a detailed equivalent circuit model for 48P-15750kVA generator, and analyzed sudden short circuit, asynchronizing phenomena of the generator by simulations using the electromagnetic transients program (ATP-EMTP), and compared the results with the experimental data.
The present study examines the breaking capability of a hybrid fault current-limiting circuit breaker (FCLCB) when a fault occurs at a distance l of 0, 1, 4 and 8km away from the terminals of the FCLCB. This hybrid FCLCB is composed of an air circuit breaker unit connected in series with a resistive or an inductive fault current limiter (FCL). In the model of the inductive FCL, a capacitance Cp is connected in parallel with the limiting coil to simulate a coil stray capacitance and a necessary additional capacitance. By means of Mayr equation, the time variation of the arc conductance in the air circuit breaker unit was estimated to find out the result of the current interruption (successful or failure interruption) for the hybrid FCLCB. The minimum limiting impedance required to allow the hybrid FCLCB to attain a successful interruption was found to be 5 and 7Ω for a resistive FCL unit and an inductive FCL unit with Cp=5nF, respectively. Further, in the presence of an inductive FCL unit with Cp=50 and 100nF, the limiting impedance needed to interrupt the fault current successfully for all fault locations was proved to be 3Ω or above. From the results of this study, it can be said that (1) the insertion of the FCL unit should be done on the basis of a coordination between the circuit breaker unit and the FCL unit and (2) connecting a circuit breaker in series with fault current limiters may enable us to use non-greenhouse gas as quenching medium for interrupting large currents.
The Metal Hydride Intermediate-Buffer (MIB) method, which enables the load following operation of the PEFC system with reformer, has been proposed. Feasibility of this system has been already confirmed by the experiment and the result shows that metal hydride is not poisoned with impurities in reformed gas. It is expected that the MIB method improves the efficiency of PEFC system especially in low load. Efficiency improvement in low load of the PEFC system for residential use is important because the average electric power consumption in general residences is about 10-20% of the peak power. In this paper the efficiency of PEFC system with MIB method is evaluated by using the concept of exergy. The exergy efficiency of this system has been calculated and compared with the conventional system as a function of load factor. The result shows that efficiency of our system is higher especially in lower load factor, but slightly lower at the rated condition than that of the conventional. The obtained relation between the load factor and the exergy efficiency has been adapted to load demand patterns for one year measured at a residence. The results show that maximum exergy efficiency of the system with the MIB method is 4.5% higher than that of the conventional system, and the system efficiency with the MIB method is higher than the conventional system above 900W of rated power. The PEFC system for residential use is being investigated mainly about 1kW class generator. It has been clarified that the PEFC system with the MIB method has an ability to improve the efficiency at 1kW rated power and the passive load following function that the conventional systems never have.
Electromagnetic field analysis coupled with motion using the tableau approach has been applied to high speed circuit breakers of eddy current repulsion mechanisms. This breaker has an opening time of 1ms and a break time less than 1 cycle (20ms). The driving part of the breaker is composed of electromagnetic repulsion mechanisms and disk springs with nonlinear characteristics. The mechanisms are composed of two fixed coils and one repulsive plate. A numeric experiment has been applied about the dynamic behavior of the electromagnetic repulsion mechanism using the equivalent circuit method. Calculation results were good agreement with both of measurement results and calculation results by FEM on an experimental model. In addition, repulsion forces depending on material conductivities have been researched.
We investigated whether a high frequency acceleration method has validity at the degradation of XLPE in case of no influence of water for realizing a lifetime test at near the operating electric field. The tests was carried out at 50Hz, 1000Hz, and 3000Hz frequency using Recessed specimen and the specimen under Needle-plane electrode system, time-to-breakdown was measured. A clear property of frequency acceleration was checked in both results of tests, and the validity of the frequency acceleration technique was shown. And we realize that frequency acceleration factor is lower than the frequency ratio at both tests of specimens. We think the reason is that the amount of accumulation of the space charge per cycle at a defect or a tree tip at high frequency is less than the accumulation at 50Hz. Moreover, tree growth time effects at the time to breakdown of Needle-plane system specimen, but it effects a little at Recessed specimen, so there is difference of acceleration rate between both specimens. The lifetime exponent of V-t characteristic, n, increases at a 3000Hz examination, so it is suggested that n has a frequency dependence.
Cross leaked methanol in the cathode of a direct methanol fuel cell is completely oxidized, however, in the cathode of a dimethyl-ether (DME) fuel cell, the cross leaked DME is not oxidized and is exhausted from the cathode. The present paper reports that active DME oxidation such as methanol oxidation does not occur on the DME cathode until both the current density and cross leaked DME concentration exceed some upper limit. There is no cross leaked DME oxidation on a cathode under normal operating conditions, in which the current density is less than 0.2A/cm2, and the DME concentration is less than 1%. The cathode potential of the direct DME fuel cell does not decrease without active DME oxidation.
This paper applies Bayesian Optimization Algorithm with Tabu Search (Tabu-BOA) to electric equipments configuration problems in a power plant. Tabu-BOA is a hybrid evolutionary computation algorithm with competent GAs and meta-heuristics. The configuration problems we consider have complex combinatorial properties, therefore, they are hard to formulate and solve via conventional mathematical programming techniques. Using the proposed method, we have solved the following problems. The complexity of the problems are increasing in order: (1) Cost Minimization of electric equipment configuration and the corresponding cabling; (2) Plus the decision of the power plant operation patterns; (3) Plus parallel operation of plural transformers, (4) Plus the change of the supply voltages (high voltage or low voltage) to the electric power load, and (5) Add the other objective, that is, both minimization of the cost and maximization of the surplus power supply.
In recent years, the electric power system becomes more and more complicated. Therefore, the supply of electric power with stability and high reliability is required. The increase of fault current has some possibility of causing step-out of generators and a large-scale blackout. Recently, the effectiveness of FCL (Fault Current Limiter) for suppression of fault current is examined. In this paper, Active type FCL which is carried out the on-off control after fault clearance is proposed. Computer simulations are carried out for 1-machine infinite bus standard model, and the system stabilization by active type FCL is confirmed.