Since Adjustable-Speed Generator (ASG) is excited by alternative voltage fed by a quick-response cycloconverter, the rotor speed can be changed continuously. The ASGs installed at some pumping-up power stations are now utilized for Automatic Frequency Control at night time and under the light load condition by changing the pumping-up power due to the rotating speed change. It is expected. on the other hand. that under the generating condition at day time ASG will be utilized for improvement of power system stability because it can change the active power and the reactive power independently of each other. This paper presents the effect of the excitation control system of ASG designed by robust pole allocation method which is one of the controller design techniques besed on H∞control theory, on the power system damping enhancement. Eigenvalue analysis and digital time simulation arc carried out for 10-machine longitudinal test power system including ASGs in order to evaluate the designed controller.
This paper investigates a multimachine control system based on the modern control theory to enhance the stability of a local multimachine power system connected to a large-scale primary power system. Most modern control theory-based designs have been proposed on the assumption of an infinite-scale primary power system, while in most actual power systems fairly large voltage and phase fluctuations are induced by various kinds of system's faults. The local multimachine control system is then designed so as to be very effective in controlling the disturbances from the primary power system. The design is improved by using no assumption of the infinite-scale primary system. In the system design, moreover, a decentralized multimachine control system is proposed so that the control system for each machine can be designed independently from the others. It is demonstrated by computer simulations that the proposed system is effective and robust in stability enhancement by using an example of local power systems even when some fluctuations in the primary power system exist.
This paper applies the decentralized H∞ control theory to interconnected multi-machine power systems. The idea is to design a local controller for each machine model with global sub-optimal H∞; control performance with considering the interactions among multi-machine systems. The sub-optimal H∞ state feedback controller for each machine is calculated by the algorithm based on the linear matrix inequality(LMI). The control input for each machine is implemented by supplementary excitation control. The disturbance to each subsystem is modeled by perturbation of the terminal voltage, which is raised by the simultaneous reactance change of transmission line. The proposed control design scheme is applied to the three-machine loop system and the three machine radial system. The frequency responses and transient responses for each machine and the global system are evaluated by numerical simulations.
This paper describes a new advanced security monitoring system for Energy Management System(EMS). In this paper, we propose a new concept called successional static monitoring. The successional static security monitoring system evaluates each snapshot which has different network state. It has been difficult for dynamic security monitoring to simulate all the restoration process, because actual restoration process includes change of network configuration and change of power supply, and all the restoration process can not be simulated successively. In order to realize this new concept, this system includes two simulators. One is Network Simulator that calculates load flow and frequency dynamic characteristic of each snapshot. The other is Dispatch Center Simulator that decides the various command to control generators and searches for the restoration routes when a black out occurs. It includes the intelligent dispatcher model that emulates the various actions of human operators. Also this system calculates the running cost of generation that satisfies trade-off for various security index. With these simulators, this system evaluates the restoration time and estimates restorable loads after contingent faults through the all restoration precess.
This paper presents the evaluation results of an integrated fuzzy logic generator controller on an analog simulator. The proposed controller is set up by using a board type computer, AD and DA conversion interfaces, and insulated amplifiers. The controller has three control loops: the first one is the voltage control loop, which has the function of automatic voltage regulator(AVR), the second one is the damping control loop, which has the function of power system stabilizer(PSS), and the last one is the speed governing control loop, which achieves the function of the speed governor. The proposed fuzzy logic control rules are simple enough so as not to require intensive computation on the computer, therefore, its on-line real time implementation is feasible. To demonstrate the effectiveness of the proposed integrated controller, experimental studies have been performed on the analog simulator(AS) at the Research Laboratory of Kyushu Electric Power Co. The results show the robustness of the proposed controller compared with conventional controllers.
This paper describes the experimental study on dynamic stability improvement of a single-machine (laboratory size 3kVA generator) connected to an infinite-bus power system using a phase shifter. A phase-shift injection is implemented by thyrister-associated fast tap-chenges based on a sliding mode control during transient conditions of generator. Digital simulation studies are also carried out to test the control scheme and the dynamic performances of system. As a result, the numerical studies show good agreement with the experimental results. The proposed controller utilizing the microcomputer is verified to damp the transient swing caused by a fault in power system.
This paper presents a method for power system damping controller design using a transfer function identification and robust stability degree assignment method. The identification procedure used in the proposed method is based on an iterative scheme introduced by K. Steiglitz and L. E. McBride. Steiglitz-McBride's algorithm provides the low order linear system models of power systems without deriving linearized state space realization from physical modelling of the power systems. By combining robust stability degree assignment method with the Steiglitz-McBride's identification technique, power system damping controllers can be designed straightfowardly. The advantage of the proposed method is as follows, • The damping controller can be designed easily even in the large scale and complicated power systems. • Real power system dynamics can be taken in to account in the controller design procedures by using measured signals. The proposed method is applied to measured signals in TEPCO real-time power system simulator as well as time domain digital simulation results. The present paper demonstrates the feasibility of synthesizing equivalent linear systems from measured data and designing effective controller using synthesized linear systems.
Since 1970s, number of small signal stability studies for large power systems have been published and significant effort has been extended to reduce the computation time and to obtain a specific set of eigenvalues. And now much work is still under research. Recently more attention has been paid to parallel processing and great effort has been made to solve power problems. This paper proposes a parallel algorithm using SI method which is suitable for parallel eigen value analysis. To confirm the effectness of proposed algorithm implemented on a message-passing hyper-cube type parallel computer, test calculations were performed using some kinds of practical power system. The results show that the proposed algorithm is 30_??_50 times faster than single CPU calculation.
NTT is developing a phosphoric acid fuel cell energy system for telecommunication co-generation systems to reduce energy costs and help preserve the environment. Fuel cells are used to provide electrical power to telecommunication equipment and the heat energy that is generated is used by the absorption refrigerator to cool the telecommunication rooms throughout the year. We fieldtested this fuel cell energy system in a telephone office for three years. Heat recovered water from fuel cell stack coolant was supplied to the absorption refrigerator and further extra-heat was recovered by a heat exchanger. The total heat recovery amount was about 86000 kcal/h (the heat recovery efficiency was 20%) under 200kW operation. The absorption refrigerator was supplied about 49000kcal/h of heat and operated with 0.7 of coefficient of performance throughout the year. The electrical efficiency was mainteined more than 38% after 13000h operation.
The effect of particles' shape on partial discharge inception electric field was investigated in oil immersed insulating system. Particles' shape effect can be evaluated by shape- parameter for copper particles. Various particles were evaluated in material, size and density on partial discharge inception electric field. The metallic particle causes the initiation voltage of partial discharge to be lower than the dielectric particles. However the property can be deteriorated by dense dielectric particles remarkably. The motion of dense dielectric particles was observed with high speed camera at the instance of partial discharge initiation. It is found that partial discharge depends on the motion of particles rather than the bridge formation of particles across the gap. Positively charged particle arrives at pressboard on negative electrode to cause partial discharge.
An accident in high voltage aerial distribution systems such as punch-through breakdown, disconnection of wire can often occur by the invasion of lightning overvoltages. This is due to the generation of creeping discharges traveling over the insulated wire surface. The detailed study on creeping discharge characteristics is a most important to the prevention of such accidents. In the previous our paper, it was clarified that when a standard lightning impulse voltage was applied to either the central line of the sample wire or the binding wire, there was a remarkable difference in the lengths of creeping discharges. In this paper, we clarify that the lengths and aspects of creeping discharges when an impulse voltage is applied to the central line of wire are significantly affected by the electric field strength of wire surface. These results will be useful to the optimum design for the insulation of aerial distribution systems.
This paper carries experimental results of surge characteristics of a concrete pole, a buried conductor and a grounding net for high impulse current with the maximum magnitude of 40kA generated by an all-weather-type mobile impulse voltage generator. The experimental results show that the grounding resistance of the grounding electrode has a current-dependence and hysteresis characteristic. Calculated results by a current-dependent grounding resistance model show a poor accuracy because it does not include the hysteresis effect. Based on the experimental results, a current- and energy-dependent grounding resistance model to describe the nonlinear surge characteristics has been developed. The model takes account of current dependency and hysteresis characteristics. Calculated results by the proposed model using the EMTP agree well with the experimental results. The proposed model is expected to be useful to an accurate simulation of a lightning surge.