Service restoration in distribution systems can be formulated as a combinatorial optimization problem. It is the problem to determine power sources for each load considering various operational constraints in distribution systems. Up to now, the problem has been dealt with using conventional methods such as branch and bounds method, expert system, neural networks, and fuzzy reasoning. Recently, modern heuristic methods such as Genetic Algorithms (GA), Simulated Annealing (SA), and Tabu Search (TS) are noticed as efficient methods for solving large combinatorial optimization problems. Moreover, Reactive Tabu Search (RTS) can solve the parameter tuning problem, which is recognized as the essential problem of the TS. Therefore, RTS, GA, and SA can be efficient search method for service restoration in distribution systems. This paper develops a reactive tabu search (RTS) for service restoration and compares RTS, GA, and PSA (Parallel SA) for the problem. The feasibility of the proposed methods is shown and compared on a typical distribution system model with promising results.
The voltage sensitivity of the bus load is important data required for power system dynamic performance studies. However, it is not straightforward to determine the sensitivity coefficients because the bus load consists of a number of load components and network elements and because their composition changes with time, weather, customers' lifestyles, and other factors. This paper describes a technique to estimate the voltage sensitivity coefficients. The technique was developed while studying the recorded bus load responses to naturally occurring disturbances. The voltage sensitivity coefficients of the Izusi 6.6kV bus load were estimated.
This paper presents an advanced method for unit commitment problem using a Genetic Algorithm and the Lagrangian Relaxation Method. Lagrangian Relaxation Method efficiently produces an optimal schedule for large-scale problem with limited constraints, but some coupling constraints, for example prohibition of simultaneous unit start-up/shut-down at same plant, can't be considered. Genetic Algorithm can easily include the complicated constraints by introduction of a penalty function. This method utilizes both advantages of the Genetic Algorithm and the Lagrangian Relaxation Method. Moreover, the introduction of heuristics simplifies genetic string manipulation which improves optimization efficiency. These include addition of limitation of modifying the schedule, adaptation of fitness function, and limitation of the crossover point based on the string expression. Numerical results have shown that the method is effective in solving the practical unit commitment problem.
Unified Power Flow Controller (UPFC) can inject voltage with the controllable magnitude and phase angle in series with a transmission line. And it can also generate or absorb controllable reactive power. UPFC is expected to be able to damp power system oscillation more effectively than power electronics applied devices such as SVG and TCSC. In this paper, a. control system design of UPFC for power system damping enhancement based on eigenvalue control method was proposed. As a result, it was made clear that the best design method for the power system damping enhancement is to determine steady-state values of UPFC control variables and control parameters of UPFC such as gains and time constants simultaneously because controllability of UPFC depends on the steady-state values of UPFC and the power flow condition. And the effectiveness of the proposed control system taking into account UPFC inverter ratings is verified by digital time simulation. Furthermore the effects of input signals to UPFC controller on small-signal stability and transient stability enhancement were studied. And it was made clear that the controller of UPFC using global information are more effective on the power system damping enhancement than that using local information because the global information has stronger observability for power system oscillation than the local information.
In future power systems, the service interruption in the electric energy supply will be easily realized by using communication networks. In order to apply the new service widely, it is important to design a transparent pricing menu for all customers. When designing the pricing menu which consists of the price and the reliability indices, it is necessary to consider that both the customer composition and the reliability of the incoming power are different among the buses. This paper evaluates the reliability differentiated supply system considering the local characteristics in power systems. The proposed method consists of three main parts. Every customer is assigned to either high reliability subset or standard reliability subset using the information of outage cost so that the total outage cost is minimized. Next, the authors determine the price ratio of high reliability menu (menu-H) to standard reliability menu (menu-L) for guiding every customer to the above assignment pattern. Further, in order to realize a consistent pricing in overall power systems, the authors propose a pricing policy that the prices of menu-L are same in every bus. Through numerical examples of a small network system, the authors investigate how the reliability differentiated pricing menu is affected bv the local characteristics in rxrwer systems.
In recent yeas, photovoltaic-thermal hybrid solar collector has been studied and developed all over the world. However, system performance of photovoltaic-thermal hybrid collector has not been clarified quantitatively because of the lack of comparison with conventional side-by-side system and of standard evaluating method for photovoltaic-thermal binary utilization system. So we conducted this comparison first, and then considered evaluating quantity. To evaluate the performance of primary solar energy converters quantitatively, several types of solar photovoltaic-thermal binary utilization system for residential buildings were discussed. Different two hybrid systems with photovoltaic-thermal hybrid collectors, side-by-side system with c-Si photovoltaic modules and liquid type flat-plate collectors have been designed and simulated. Under the constant installation area of 33.6m2, electrical load of 4, 032kWh/yr and DHW (domestic hot water) load of 7, 282kWh/yr, we compared performance of the hybrid systems with the side-by-side system in terms of solar energy fraction. As an annual result, the best solar energy fraction was achieved by the hybrid system, which produced 75.4% and was 6.5% higher than the side-by-side system, which produced 68.9%. Moreover, it was found that the hybrid system becomes better than the side-by-side system with increase of DHW load.
The fall-of-potential method is commonly used to measure the grounding resistance, depending on the measuring area. In this paper, a numerical simulation was carried out to obtain the grounding resistance. The angle and distance between the current electrode C and potential electrode P were the keys for this calculation, and this was compared with the grounding resistance for the rod electrode having a theoretical solution. It was measured in the electrolytic tank to obtain the accuracy of the estimation. As a result, the theoretical results were agreed with the experimental values, it was found that this method could estimate the location of the grounding electrode and the experimental value.
We have been observing lightning discharges by UHF Interferometer, and we show comparison between lightning during winter thunderstorms and during summer ones. The main objective of the comparison is further understanding of features of lightning during winter storms, especially of positive cloud to ground flashes. For this purpose we compare negative and positive flashes on UHF radiation and pulse density, and we perform two dimensional mappings of UHF radiation sources. Moreover we show the three dimensional imaging for a cloud flash, and we discuss the relationship between the altitude of leader progressions and atmospheric temperature profiles as a function of height. We also show the estimated velocite of leader progressions and find no discrepancy with the former results obtained by Proctor.
This paper describes dielectric strength of oil immersed insulation for DC voltage and it's polarity reversal voltage. Dielectric strength for polarity reversal voltage is a key point to rationally design HVDC insulation system. Authors investigate the breakdown characteristics of creepage insulation structures for DC and polarity reversal voltages. Especially, the partially concentrated stress at distant portion from the electrodes is investigated in compared with the stress near the electrodes. As the results, it is clarified that the partially concentrated stress at distant portion from the electrode does not necessarily cause the initiation of breakdown. The stress near the electrodes tends to initiate breakdown for DC voltage. The creepage insulation is not much affected by the polarity reversal voltage. These results in this paper are applied to optimum insulation design of the oil immersed 500kV HVDC apparatus in Kiisuidou Project.
Oxygen reduction mechanism on Au meniscus electrode in molten Li-Na carbonate at 650°C has been studied by analyzing the electrode reaction resistance measured with current double pulse method. The meniscus electrode composed of Au gauze were adhered onto the molten carbonates electrolyte tyle and sprayed CO2-O2-N2 mixed reactant gases at the flow rate of 100cm3/min, Investigating the dependencies of the electrode reaction resistances on CO2, O2 partial pressure and the i-V relations for O2 reduction, it was assumed to be atomic O formed by dissociation of O2 molecules at the electrode interface as the electrochemical reduction species.
A persistent current switch (PCS) used in the large-scale SMES system needs to have high OFF resistance as well as zero ON resistance for efficient load-leveling operations. So far, the authors have successfully developed NbTi mechanical PCS, which realizes zero contact resistance, infinite OFF resistance, and switch current capacity over 200 A. Considering practical use of the PCS, the switch current capacity has to be further increased to obtain much larger rated current of 100 kA order for the GWh class SMES system. This paper describes the switch current capacity and quench characteristics in the parallel PCS circuit which consists of two NbTi mechanical PCS's. Effects of current distribution and quench property of each single PCS are especially investigated in detail. To clarify the posterior quench mechanism at the time when both PCS's are quenched, quench characteristics on the time are also investigated by applied pulsed current. It was found that each PCS in the parallel circuit has to obtain identical quench current and distribute current uniformly so as to achieve the theoretical maximum switch current capacity. Additionally, existence of quench time lag is definitely confirmed. Quench time lag is the key property to make clear the succeeding quench mechanism.
The health effect of small currents induced in a human body exposed to the power frequency electric field has been investigated since early 1970s. The distributions of induced current density inside grounded and ungrounded human models have been quantified; however, such internal distributions have been little analyzed as a function of the model heights above the ground. In order to analyze the effect of the human body heights above the ground on the internal current distributions, the axisymmetrical human model is used. The finite element method is applied for the human model placed at heights of 0.01, 0.05, 0. 1 and 1.0m above the ground under a uniform 60Hz electric field of 1kV/n. The calculations lead to the quantification of the characteristics of the internal current density inside an ungrounded human model. The calculated results have demonstrated the adequacy of the experimental results reported by Kaune et al. who used a 3-dimensional miniature human model.
Recently, substations have been increasingly installed in underground of urban areas to provide a stable power supply, and gas-insulated substation equipment is popular due to its compactness, incombustibility and explosion-proof to prevent disasters. So, 275kV-150MVA gas-insulated shunt reactor, the world largest capacity as gas insulated type, was developed and commercialized. This paper describes research conducted on the development of a gas-cooled, large-capacity, gas-insulated shunt reactor. Authors carried out by rapid wave surge overvoltage test, numerical analysis of thermal fluid, measurement of winding temperature by using optical fiber and verification test on reliability of construction. This reactor has operated normally for three years. The operating performance of the reactor in this term has been confirmed by gas analysis, and no abnormal phenomenon has been demonstrated.