The introduction of distributed power supplies, such as a cogeneration system (CGS) and renewable power generation, has been promoted with a rise of the concern about global environment issues, and deregulation of the electricity market. Although the total capacity of the distributed power supplies is still small, many researchers and experts in industrial, governmental and academic sectors seem to have a great interest in the possibility that distributed energy systems can form a novel energy system which can complement an existing centralized large-scale energy supply system. In this paper, the author reviews a future prospect and issues of distributed energy systems.
The electric power transactions are classified into pool transactions and bilateral contracts as well as security transactions. A certain transaction level of, for example, bilateral contracts may affect pool transactions by causing transmission congestion etc. In this paper, we will discuss how both the market and the bilateral transaction participants share the operation cost and charge for using network in consideration of power transmission loss allocation among generators. Following these discussions, we present an optimal scheduling method for pool participants. To ascertain the effectiveness of the proposed scheduling algorithm and to show how the bilateral contract level affects the pool operation, we will demonstrate various simulation results for a model power system of 8 units 44 bus power system.
Sending voltage profile of distribution feeder is controlled by changing a tap of distribution transformer. In a distribution network with distributed generators, for reasons of effect of reversed flows from them and existence of a great number of sending voltage profile candidates, it is not easy to control sending voltage profile within the acceptable voltage limit. In this paper, in order to determine the optimal sending voltage profile of distribution transformer in a distribution network with distributed generators, the authors propose a new method to determine the optimal sending voltage profile so as to minimize total number of tap position's change per day under constraints of acceptable voltage limit. In the proposed method, after calculating acceptable range of three phase voltage of distribution feeder, the optimal profile of tap position within the calculated acceptable voltage range is determined among these candidates by using reduced ordered binary decision diagram (ROBDD) which is an efficient enumeration algorithm. In order to check the validity of the proposed method, numerical simulations are carried out for a distribution network model with a distributed generator.
Recently, wind power generation is increasing in the world. In the wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as one mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two-mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study.
In order to get wind energy effectively, the pole-change-type induction generators are used as the wind turbine generators. Otherwise, the pole-change-type induction generator causes the voltage dips at pole changing time. To keep the power quality, it is important to know the state change of the generator operation. Therefore, the authors have studied a state criterion of generator using the tower shadow effect, which is the active power oscillation caused by a rotation torque drop when the tower and the turbine blade overlap each other. In this paper, an improved identification method of oscillation frequency, which is the criterion of wind turbine generator operation, is proposed. A proposed method is applied to measured data and shows that it gives the good results.
A simple model of output power of a thermal power plant for demand and frequency change has been developed. The model is evaluated comparing with the actual plant output data in order to demonstrate that the model covers plant dynamics over wide range normal operation. To minimize the variance of the error of output power between model output and actual data, the speed governing effects was proven to be much smaller than its design value.
3kV 600A 4H-SiC high temperature flat package type diodes have been developed for use in electricity supply, which are a pressure contact flat package type and include five 6mm × 6mm SiC diode chips. The flat package type diodes have excellent electrical performances at high temperature.
In AC electric Railway, three-phase voltage is changed into the single-phase circuit of two circuits with the Scott-connected transformer. If it becomes large unbalancing of the load between single-phase circuits, voltage fluctuation becomes large on three-phase side. Then, Railway Static Power Conditioner (RPC) was developed for the purpose of controlling voltage fluctuation on three-phase side. An RPC is comprised of a pair of self-commutated PWM inverters. These inverters connect the main phase and teaser feeding buses, coupled with a DC side capacitor such as a Back-To-Back (BTB) converter. In this way, the two self-commutated inverters can act as a static var compensator (SVC) to compensate for the reactive power and as an active power accommodator from one feeding bus to another. 20MVA/60kV RPCs started commercial operation in 2002 at each two substations on the newly extended Tohoku Shinkansen for compensating voltage fluctuation on three-phase side caused by traction loads, absorbing harmonic current. The results of operational testing indicate that an RPC can accommodate single-phase loads such as those of PWM-controlled Shinkansen and thyristor phase-controlled Shinkansen, and handle the exciting rush current of transformers, as well as compensate for harmonics successfully.
This paper presents a design and testing of a new high-speed electromagnetic driving mechanism for a high-voltage vacuum circuit breaker (VCB). This mechanism is based on a high-speed electromagnetic repulsion and a permanent magnet spring (PMS). This PMS is introduced instead of the conventional disk spring due to its low spring energy and more suitable force characteristics for VCB application. The PMS has been optimally designed by the 3d non-linear finite-elements magnetic field analysis and investigated its internal friction and eddy-current effect. Furthermore, we calculated the dynamic of this mechanism coupling with the electromagnetic field and circuit analysis, in order to satisfy the operating characteristics—contact velocity, response time and so on, required for the high-speed VCB. A prototype VCB, which was built based on the above analysis shows sufficient operating performance. Finally, the short circuit interruption tests were carried out with this prototype breaker, and we have been able to verify its satisfying performance.
This paper describes the measuring and protection method for the abnormal rise of magnetizing inrush current in a divided type 3 CTs system. By divided type 3 CTs system, it is possible to measure the primary phase current and zero phase current at the same time. In this reason, the divided type 3 CTs system is widely used for the measurement of high voltage distribution line by simply clamping the each phase lines with 3CTs. For the accurate measurement of the phase current and zero phase current, the internal residual current in CT should be small as possible. It is reported that the abnormal rise of the residual current is generated in the practical field use and several ten ampere (converted to the primary current value) is observed in some case. The abnormal rise of the residual current is caused by the primary magnetizing inrush current or by the sum of the influence by electromagnetic field of the nearby conductors. The magnetizing inrush current is caused by the magnetic saturation of the core of CT. It is difficult to eliminate the abnormal residual current by using the bigger size of core. In our test, we used the active elements and independent feed back coils around the right and left core of CT. By using the feed back current from these coils it was observed that the magnetic saturation of the core is improved and the magnetizing inrush current can be controlled.
The operating characteristics and operation procedure of the closed loop experimental facility under subsonic power generation have been investigated by means of time-dependent quasi-one-dimensional numerical simulations. It was found that there are two ways of operation for the subsonic power generation, which are (1)a subsonic operation both under non-power and power generation and (2)a supersonic operation under non-power generation and subsonic operation under power generation. For the operation(1), Mach number at channel inlet decreases to ˜0.6, therefore it is required to generate plasma under this Mach number. On the other hand, if the plasma cannot be generated, the operation(2) needs to be carried out. In this case, a shock wave appears in the generator channel, then the influence of a large pressure change and a vibration caused by a shock wave in the generator channel needs to be considered.