The key to today’s energy revolution involves turning the resource backwards from large power plants hundreds of kilometers away to a load center by riding the rapidly accelerating technology wave forward. This paper describes not only the technologies being developed today-distributed generation, IT-based energy management systems, and demand-side area network- but also changing value of customers and restructured power market that will populate the new energy landscape.
Recently, numbers of distributed generators (DGs) connected to distribution systems have been increasing. It is important to know how large capacity of generators output is permitted when the generators are connected to the distribution system under the regulated condition of line voltage, line current and power factor of the generator connection point. The authors show difference of maximum output of DGs caused by various voltage regulation systems in an average length system and a long length system by load flow calculation. The voltage regulation systems include six following types; (1) no control equipment, (2) SVC (Static Var Compensator), (3) existing SVR (Step Voltage Regulator), (4) reverse flow type SVR which operates even in reverse flow, (5) existing SVR and SVC, (6) reverse flow type SVR and SVC. A synchlonous generator is considered as DG in this paper. The numerical simulations showed that the maximum output of the DG is about 3300[kW] in the average length system and about 540[kW] in the long length system. However, maximum output of the DG increased up to about 3750[kW] in the case of existence of a SVC, further capacity of SVC decreased in the case of exchange to the reverse power flow type SVR in the long length system.
It is expected that a number of dispersed generators interconnecting with power distribution systems will be increased with progress of deregulation in electric power industry. In order to allow large capacity of the interconnection, a certain current limitation measure is required in present distribution systems because of allowable short circuit capacity as a restriction. One of effective measures is fault current limiter (FCL) which suppress short circuit current within a time of half cycle. However, a required performance of FCL applied to dispersed generators is not made clear. The authors look for necessary conditions on the FCL performance for above-mentioned purpose using EMTP simulation. This paper presents necessary performance of FCL, which includes a commutation type FCL with resistance and reactance as a limitation element.
Understanding actual characteristics of a power system with recorded time series data is of great importance, for example, to improve the performance of the system. Although system identification is a well-known technique to achieve this goal, its applicability to a certain system should be examined for the particular case because its accuracy highly depends on the inherent characteristics of the system. While many papers have discussed application of a system identification technique to a power system, few papers have examined its applicability to the actual data of a power system. This paper presents a new system identification method to estimate characteristics of a power system while using output of intermittent generators or fluctuating loads as an external disturbance. The method employs cross spectra and coherence as a key factor in the identification; it estimates a transfer function of a power system, contribution of observed disturbance to total disturbance, etc. The method is applied to time series data of two model systems: simulation results and measured data of an isolated power system with diesel generators. The study gives satisfactory results; implication on the accuracy of the method is discussed through the sample studies.
On-site generator, such as CGS (cogeneration system), is allegedly considered to be an effective end-use energy system in order to accomplish primary energy conservation, CO2 emission mitigation and system cost reduction, which characteristics eventually improve the whole performance of an existing energy system for the future. Considering the drawback of installing an end-use CGS into the customer with small or middle scale floor space, however, it is difficult to achieve those distinctive features because the thermal-electricity ratio of CGS does not always be in agreement with that of customer energy demand. In order to overcome that matching deficiency, it is hence better to organize an on-site generator network based on mutual electricity and heating transmission. But focusing on some cogenerators underlying their behaviors on maximizing their own profits, this on-site network, which situation corresponds to a grand coalition, is not necessarily established because of each cogenerator’s motivation to form a partial coalition and acquire its own profit as much as possible. In this paper, we attempt to analyze the optimal operation of an on-site generator network and identify by applying the nucleolus of the cooperative game theory the optimal benefit allocation strategy in order for the cogenerators to construct the network. Regarding the installation site of this network, the center of Tokyo area is assumed, which locational information includes floor space and so forth through a GIS (geographic information system) database. The results from the nucleolus suggest that all districts should impartially obtain the benefit from organizing network for the purpose of jointly attaining the system total cost reduction.
The authors have proposed Flexible, Reliable and Intelligent ENergy Delivery System (called “FRIENDS”), which is a new concept for a future power distribution system. One of the most important feature of FRIENDS is to be able to manage the reliability of power supply. In this paper, FRIENDS and a conventional distribution system are compared quantitatively in supply reliability and cost through time sequential Monte Carlo simulation.
It is required for the energy systems to satisfy simultaneous solutions to the problems, such as cost reduction, global warming, assurance of energy security, and resource conservation. To evaluate optimal end-use energy systems from the stand point of CO2 emissions, we apply a comprehensive approach based on the life cycle assessment. Several combinations of electricity and heat supplying systems are compared. They include the electricity driven heat pump, gas engine co-generation, absorption refrigeration and so on. Calculations represent total CO2 emission by energy consumption of several operation patterns, based on the actual data of energy demand, CO2 intensity of the grid electricity and the equipment specifications. The results indicate that CO2 emissions can be minimized by maximum utilization of electricity from the grid.
This paper proposes a multi-agent approach to decentralized power system restoration for a distribution system network. The proposed method consists of several Feeder Agents (FAGs) and Load Agents (LAGs). LAG corresponds to the customer load, while a FAG is developed to act as a manager for the decision process. From the simulation results, it can be seen the proposed multi-agent system could reach the right solution by making use of only local information. This means that the proposed multi-agent restoration system is a promising approach to more large-scale distribution networks.
This paper presents high-order harmonic resonance phenomena of voltage sourced converter (VSC). When a voltage sourced converter is connected to power system with cables, there is possibility that minute high-order harmonic voltages of a voltage sourced converter are magnified by a series resonance and a parallel resonance, and high-order harmonic resonance phenomena are found by this study. The cause of high-order harmonic resonance phenomena is investigated and figured out by the analysis using EMTP. In addition, it is verified that high-order harmonic resonance phenomena occur as a practical matter.
It is indispensable to forecast accurately the very short-term load demand to avoid undesirable disturbances in power system operations which deteriorate economical generations. The authors have so far developed a short-term forecasting method by using Local Fuzzy Reconstruction Method, a variant of the methods based on the chaos theory. However, this approach is unable to give accurate forecasting results in case where load demand consecutively exceeds the historical maximum or is lower than the minimum because forecasting is performed by the historical data themselves. Also, in forecasting holidays in summer, forecasting result of weekdays might appear due to similar demand trend. This paper presents novel demand forecasting methods that are able to make accurate forecasts by resolving the above mentioned problems. First, the new method improves the accuracy by extrapolating forecasted transition from the current point. Secondly, to eliminate miss forecast which may be occurred on holidays in summer, historical data are labeled by the information of the day of the week to distinguish similarly behaved weekdays’ load patterns. The proposed methods are applied to 10, 30, and 60 minutes ahead demand forecasting, and the accuracy is improved 10% to 20% compared with the method previously proposed.
There are 50Hz and 60Hz power systems in Japan, which are interconnected by power electronics based static type frequency converter station. Frequency converter can be realized by using Adjustable Speed Generators/Motors (ASGMs), which are excited by AC voltage, and so-called rotary type frequency converter. The rotary type frequency converter can also function as a power system stabilizer by effectively utilizing rotational energy stored in rotors. Nonlinear excitation control for the rotary type frequency converter is proposed to enhance performance of the rotational energy utilization and to improve stability of power system. The control performance is examined for a power system model by digital dynamic simulation. It is made clear that the proposed nonlinear excitation control is effective even though local information of the rotary type frequency converter is just used and that it has robustness against various load flow conditions.
This paper presents a new approach to optimal voltage and reactive power control based on a particle swarm optimization (PSO). The proposed method switches one of controller by PSO and considers control times to the objective function. Therefore, this method can give the control process. The methods which give the control process have not been proposed in the algorithm of PSO. The effectiveness of the proposed method is demonstrated by practical 15-bus and 118-bus systems.
This paper presents the results of work flow analysis of generation scheduling and power system operation on the assumption that further deregulation is introduced into Japanese electric utility. California system and PJM system are tested as they are introduced into Japan. It was made clear that the time required for making the plan to operate the grid for the next day is acceptable for the Japanese system when a spot market is founded. Flow simulation of jobs of the power system operation is done based on IDEF0 method using flow charts similar to Petri net.
Recent results have shown that several H2 and H2-related problems can be formulated as a convex optimization problem involving linear matrix inequalities (LMIs) with a finite number of variables. This paper presents an LMI-based robust H2 controller design for damping oscillations in power systems. The proposed controller uses full state feedback. The feedback gain matrix is obtained as the solution of a linear matrix inequality. The technique is illustrated with applications to the design of stabilizer for a typical single-machine infinite-bus (SMIB) and a multimachine power system. The LMI based control ensures adequate damping for widely varying system operating conditions and is compared with conventional power system stabilizer (CPSS).
The horizontal electric field (Er) contains useful information for estimating position of thundercloud. Unfortunately, it is difficult to detect horizontal electric field (Er) due to electric field component on the earth surface is almost a vertical component. We propose a new idea for horizontal electric field (Er) detection. We developed two types of horizontal electric field meter (HEFM), i. e., a fixed electrode-type and a rotating electrode-type, and evaluated their performance experimentally and found that they have sufficient sensitivity to Er to estimate the direction of thundercloud. In this paper, we present the result of performance evaluation and also present an electric field data measured by HEFMs as examples.
We measured AC transport current losses in three kinds of thin film YBCO coated conductors made by different processes. The results showed that the loss characteristics were different and that some of the conductors did not follow the Norris strip model which was generally considered to well explain the loss characteristics of YBCO conductors. In the paper, an analytical model in which distribution of critical current density and n value of the conductor are taken into consideration is proposed to describe the AC transport current loss characteristics more generally than the Norris strip and elliptical models. It is shown that the analytical model well explain the measured loss characteristics of the three kinds of the conductors.
Various noises produced by corona discharges from high voltage transmission lines are the important considerations in line design. HVAC transmission lines must be designed to satisfy national environmental regulations too. Therefore, it is necessary for line designers to pre-evaluate environmental problems using prediction tools. In this paper, an environmental design software, TLCALC 2001 for AC transmission lines as a comprehensive window program is introduced. It has 6 modules including audible noise, radio noise, television noise, magnetic field, electric field and conductor surface gradient module. TLCALC 2001 has solved some of the problems of the existing foreign tools and has several advantages over those. 1) It is a common tool that has solved calculating limitations of foreign formulas. 2) It has a wide application range and enhanced prediction accuracy. 3) It can be applied to almost all transmission line configurations in Korea. 4) Experienced designers can get calculation results within about 15 minutes. As the use of TLCALC 2001 is easy and practical, it will be applied to the environmentally friendly design and construction of transmission lines. It is expected that public complaints and social environmental costs will be considerably reduced by the use of TLCALC 2001 in the future.
A method for estimating an anode-fall voltage of an arc discharge was developed. By using this method, the anode-fall voltages were evaluated for air arcs in atmosphere burning between the electrodes of copper, silver and tungsten. The anode-fall voltages Va of air arcs proved to be about 1.2, 4.5 and 1.2V for the copper, silver and tungsten electrodes respectively and were found to be almost independent of the ac half-wave current from 350 up to 1500Apeak. From the above results, the difference in the anode material seems to lead to the variation in the anode-fall voltage.
Abstract: Class-10A solid-core insulators (BIL 90kV) have been used instead of class-6A pin insulators (BIL 60kV) in order to improve the insulation level of distribution lines. However, lightning protective devices attached to pole transformers may have the effect of reducing the overvoltages on phase conductors. We have investigated the lightning protection effect of devices attached to pole transformers by experiment and analysis using the EMTP (Electro-Magnetic Transients Program). The sparkover rate changes from 2.0˜3.3% to 5.5˜9.9% and increases 2.4˜2.8 times when the line insulator of the phase conductors is changed from class-10A to class-6A. It is thought that the insulation level of the line insulator can be reduced depending upon the local particularities, such as number of installed transformers, frequency of direct lightning stroke to the distribution line, and so on although the overall fault rate may increase to some extent.
For rationalizing equipment insulation level which can subsequently lead to reductions in the cost of substation equipment such as GIS’s and transformers, it is necessary to reexamine insulating test voltages by investigating the method of evaluating lightning surge waveforms in terms of the equivalent standard lightning impulse waveforms. This paper describes the evaluation method for real surges (called non-standard lightning impulse waveform), based on insulation characteristics of gas gaps. The method is applied to typical surges in the lightning surge time region for various UHV and 500kV systems and it is obtained that the equivalent peak values of the standard lightning impulse waveform are possibly reduced by 20 to 30 percents.
The present paper describes a prediction method of the dielectric strength of the air in gas temperature range of 300-3500K. First, the equilibrium composition of the air at gas temperatures of 300-3500K was calculated through Saha and Guldburg-Waage equations. Secondly, the electron energy distribution function (EEDF) was calculated by an adoption of the two-term expansion of Boltzmann equation. Finally, the effective ionization coefficient α was derived from the EEDF obtained. The critical reduced electric field strength (E/N)cr, which gives zero effective ionization coefficient α=0, was obtained at gas temperatures of 300-3500K. The result indicates that (E/N)cr decreases as the gas temperature increases from 1500K to 3500K, which is due mainly to an increase in the mole fraction of NO molecule which has a much lower ionization potential compared with N2 and O2. This calculated result fairly agrees with an experimental one.