This paper describes a method of stabilizing control for a dual-excited synchronous generator connected to an infinite-bus system. The method is based on a combination control scheme in which is used a phase control of resultant flux-linkage produced by d-and q-axis field windings jointly with the feedback controls of generator terminal voltage and electrical output. The proposed controls consisting of two excitation systems are implemented on a laboratory size 3kVA generator with a personal computer acting as the digital controller. The experimental results show that the synthesized control method is suitable for improving the transient stability subjected to large disturbances in a dual-excited synchronous generator infinite-bus system.
In this paper, an expert system is developed for re-energizing an EHV power system after a complete blackout. In order to restore the blackout areas which are not restored by operations based on the prescribed operation manual, we newly supplement several operations. These operations are selected to realize three restorative scenarios. The operations are executed at dispatch commands. We introduce several conditions so that the expert system can select appropriate commands as the restoration proceeds. The dispatch commands are classified into several groups, and their data are described in several objects. Those objects are controlled under one object, where such information as names of command groups, priority among the groups, etc., is written. By editing the contents of the objects, we can easily modify dispatch commands and restoration process. The operator checks the selected commands. If he judges them appropriate, then he issue them. If not he can reject, reserve, or replace them. The expert system is tested under various conditions to verify that it functions as designed.
Recovery characteristics of a YBa2Cu3O7-y high-temperature superconductor after its quenching are experimentally investigated in this paper. We examine zigzag-shape superconducting elements with 310mm in effective length and 1.5mm×1mm in cross-section. AC current injection tests are carried out. It is clarified that the high-temperature superconducting element has a quick transition characteristic between the super- and normal-conducting states. The test elements recover to zero impedance state from high impedance state just after removing the over-current when the magnitude of accumulated heats due to the over-current during the quenching period is less than 1 J. Furthermore, it is found from our experiments that the critical current level might be reduced by some self-magnetization due to a high current during the quenching period.
This paper describes a new approach to the analysis of the back swing phenomena in multimachine power systems. When a short circuit fault occurs in a power system, some generators decelerate in a short period right after the fault in some cases. The phenomenon called back swing is caused by the transient responses in armature winding of synchronous machines and in transmission lines. To represent the back swing in detail by a mathematical model, these transient behaviors have to be described by sets of differential equations. Then not only the order of differential equations increases, but the convenient expression of transmission system by a set of node equations becomes useless. In this paper an equivalent model of power system for the simple representation of the back swing, has been proposed. First, an impedance for each machine that represents the transient of transmission system, has been introduced. It is assembled into the differential equations associated with armature winding response. Then the transmission system is represented by a constant impedance matrix. This model makes it possible to calculate the transient behavior of armature flux in multi-machine power systems. The transient torque brought to the rotor shaft by the flux, is directly calculated and it represents the back swing phenomena effectively.
Owing to the recent increase in voltage and the capacity of electric power installations and high voltage equipments, the necessity for the research on electromagnetic interference (EMI) has been recognized for the compatible maintenance of electromagnetic environment between electric power systems and electronic equipments. In this field, however, there are not a few significant technical problems, one of which is the effect of pulsed corona noises of negative polarity in high voltage lines, precipitators and electro-coating machines. This paper describes the results of the experimental research and investigations for determining to what extent air streams affect corona noise in VHF band with a needle-plane electrode at atmospheric pressure. The VHF corona noise characteristics showed distinctive variation with the different radius of curvature of needle electrodes and air flow velocity. Specifically, for large curvature, the VHF corona noise is sensitive for air flow velocity. These observations demonstrate the effect of current enhancement in wind-blown coronas. These results indicate that the wind acts to increase the electric field to cause the disruption of negative ion cloud near the needle electrode and to cause the large amplitude corona pulse and accompanying rise in VHF noise level.
This paper describes a new approach for electric generation expansion planning of interconnected systems. The proposed approach is based on the Benders Decomposition technique. That is, the large scale generation expansion planning is divided into one master problem which is constituted by general Economic Load Dispatch (ELD) problem, and several subproblems which are composed of smaller scale isolated system generation expansion planning. Power exchanges between each system are calculated by using Linear Programming in master problem. On the other side, generation expansion plans are determined by the conventional approach in subproblems. Since the large scale interconnected system planning is decomposed into several smaller scale isolated system planning, both computation time and memory can be largely saved. In addition, the generation capacity installation and the fuel cost can be also expected to reduce by regulating the power exchanges and sharing common reserve of the interconnected system.
This paper describes overvoltage caused by disconnecting a lot of motor-loads on a power distribution line with power-factor-correcting capacitors during a transmission line open-phase. The overvoltage phenomena are studied by a field test, a steady-state analysis and a transient analysis. Experimental results show that the line-to-line voltage on a 6.6kV distribution line with an open-phase 22kV transmission line amounts to 1.7 per unit. The overvoltages are caused by two types of resonance. One is the linear circuit resonance between the power-factor-correcting capacitors and the secondary side impedance of motors. The difference between positive components and negative ones of the impedance produces the resonance. The other is the non linear circuit resonance between the power-factor-correcting capacitors and the saturated reactances of a transformer.
In an interruption chamber of Gas Circuit Breaker (GCB), a current is interrupted at current zero. SF6 gas is blown to an arc occurred between contacts. In this process, the gas blown from puffer chamber flows through a nozzle at high speed. For this reason, a supersonic region is formed and a pressure is decreased. It often causes a fault of interruption. In the downstream, a shock wave is often occurred. In recent years, these phenomena are investigated through experiments and numerical simulations. In order to design superior and reliable GCB's, it is very important to optimize the position of shock wave for an improvement of an interruption capability and stabilize the shock wave for stabilizing an interruption performance clarifying the uncertainty limit of supersonic region caused by uncertainty of manufacturing and using conditions. However, these techniques have not been developed yet. In the present paper, a new simulation method is proposed in order to design GCB's which have superior interruption capability. The method proposed by an author to include uncertainty of manufacturing and using conditions is combined with a usual code to solve Navier-Stokes equations. It is shown by using this method that the supersonic region is able to be controlled by optimizing the relationship at current zero between a fixed arc contact and a ditch designed in the nozzle, and that an uncertainty limit of the supersonic region is able to be clarified.
With the increase of the size and capacity of electric power systems and the growth of widespread interconnections, the problem of power oscillations due to the reduced system damping has become increasingly serious. As a Super-Conducting Magnetic Energy Storage (SMES) unit with a self-commutated converter is capable of controlling both the active (P) and reactive (Q) power simultaneously and quickly, increasing attention has been focused recently on power system stabilization by SMES control. This paper describes the effects of SMES control on the damping of power oscillations. By examining the case of a single generator connected to an infinite bus through both theoretical analyses and experimental tests (performed with a SMES unit with maximum stored energy of 16kJ and an artificial model system), the difference in the effects between P and Q control of SMES is clarified as follows: (1) In the case of P control, as the SMES unit is placed closer to the terminal of the generator, the power oscillations will decay more rapidly. (2) In the case of Q control, it is most effective to install the SMES unit near the mid point of the system. (3) As compared P control with Q control, the former is more effective than the latter based on the conditions that the SMES unit location and the control gain are the same.
Diving and surfacing floats provided useful means for ocean measurements. A new diving and surfacing float (pop-up float) is developed by using an electro-chemical engine. It dives with its own weight, and surfaces with buoyancy of oxygen and hydrogen gases produced by electrolyzing water. When oxygen and hydrogen burn by lightening and change into water, the float can dive again. Therefore it can dive and surface repeatedly. The production of oxygen and hydrogen with electlysis of water and their burning by lightening make a completely closed cycle, and there occured no broblems like waste gas. The preliminary tests were conducted in the sea of the depth of 33 meters and their results were disscussed for practical applications of the float.