Yasuji Sekine

A method for identification of effective locations of variable impedance apparatus on enhancement of steady-state stability in large scale power systems

Variable impedance apparatus such as a static VAr compensator (SVC) and a variable series capacitor (VSC) can improve the steady-state stability of a power system if they are located appropriately. The present paper proposes an index for identifying the location of SVC and VSC in large scale power systems for effective damping. The index is called LIED (location index for effective damping) by the authors. Since LIED can be computed quickly for large scale power systems which have more than two hundred generators without conducting a number of digital simulations and eigenvalue analyses, it is valuable for the system planner who needs to identify the effective location of SVC and VSC. The proposed index is applied to the New England test system and its validity is demonstrated through digital simulations. >

Cascaded voltage collapse

The dynamic phenomena of power system voltage collapse are analyzed by the method of dynamic simulation using induction motor models. From the viewpoint of dynamic phenomena, the voltage collapse starts locally at the weakest node and spreads out to the other weak nodes. The main conclusions drawn from this study are as follows. The voltage can be recovered, even after the node voltage is lowered beyond its static critical value. The operating state corresponding to the lower voltage solution is not always unstable. It could be stable depending upon the dynamic characteristics of individual loads, even if they are not of constant impedance type. The voltage collapse is initiated at the weakest node and spreads out to the other weak nodes. These results can be applied to radial voltage collapse phenomena. >

Reverse action of on-load tap changer in association with voltage collapse

A discussion is presented of the reverse action that occurs when the secondary voltage of a transformer is pulled down and the tap position of an on-load tap changer is raised to increase the secondary voltage. A dynamic model of an induction motor is adopted as a load model simulating this kind of reverse action during voltage collapse. The transient mechanisms of the reverse action are analyzed using P-V curves. It is found that the reverse action caused by on-load tap changers may cause the operating condition to deteriorate in a heavily loaded power system where cascaded voltage collapse may occur. >

Expert system for fault section estimation of power systems using time-sequence information

Abstract Rapid and correct fault section estimation is vital for power system restoration. This is particularly true for complicated multiple faults. This paper presents an expert system for power system fault section estimation using information including operating times of actuated relays and tripped circuit breakers. The inference is executed by transmitting timed-event markers in the cause-effect network proposed in an earlier paper. Since the proposed system can handle information on the operations of relays and circuit breakers with the aid of time sequence information, it can infer fault sections correctly even for complicated multiple faults. In addition, since the number of generated fault section candidates can be decreased, the inference speed is improved significantly. The proposed system has been tested for two examples. It has been shown that the inference speed and accuracy of the method proposed in this paper are much better than those of the one proposed earlier which does not use time information. The inference speed is also fast enough for real-time use.

Prospects of expert systems in power system operation

Abstract Expert systems for power system operation are surveyed from methodological and systems points of view. First, the logic- and heuristic-based methodologies for dealing with knowledge in computer software — the core of expert systems — are outlined. This is followed by an overview of the current applications and limitations of expert systems in power system operation. Finally, the future possibilities and prospects are evaluated.

Fast monitoring and optimal preventive control of voltage instability

Abstract This paper discusses a new method for monitoring and controlling to prevent voltage instability in electrical power systems. Voltage instability phenomena or voltage collapse may occur at the critical loadflow point in a static sense. From the system operators viewpoint, this critical point must be carefully monitored in a heavily loaded power system. In addition, the operators need to take an adequate control action when the current operating state approaches the critical point. These processes require very fast computation. Hence special attention is paid to the required computing time and on-line applicability. Monitoring methodology proposed here is based upon the multiple loadflow solutions and sensitivity analysis. The complex-valued multiple loadflow calculation method, which has already been developed by the authors, is free from the numerical instability in calculating the lower voltage solution. By using this algorithm, the operating personnel can monitor the lower voltage loadflow solution corresponding to the current operating condition. The critical point is calculated approximately using these two loadflow solutions, and the load forecast very quickly for on-line usage. The estimation error of the critical point becomes very small as the operating state becomes closer to the critical point. The existing preventive control against voltage collapse is based on the operators experience, not on a theoretical basis. The preventive control proposed here gives the optimal operations of various kinds of control equipment in the sense that the total demand margin is enlarged most effectively. Control variables consist of voltage/active power setting values at generator terminals, switched capacitors, and tap ratios of OLTCs (on load tap chargers). The resultant control action satisfies all the constraints about bus voltages, power flows, etc. Its effectiveness is demonstrated by using several numerical examples.

Microprocessors in electric power systems

Abstract The present status of microprocessor applications in various fields of electric power systems is summarized. Special attention is directed towards development trends in the protection field where microprocessor applications are expected to cope with the increasingly stringent requirements for electric power supply reliability. Also discussed are the history, roles, design philosophy and basic schemes of microprocessor-based protective relaying systems. Only recently has their application reached a practical stage after long-term study and repeated field tests.

Application of power electronics technologies to the 21st century's bulk power transmission in Japan

Abstract The electric power industry in Japan is now carrying out a nation-wide research and development programme for the effective application of power electronics technologies to the bulk transmission network and interconnected power systems for the 21st century. The programme will continue for eight years funded by ten power utilities and subsidy from the national government. The research and development programme specifically consists of the following three study projects: AC high-voltage/large-current transmission (feasibility study on enhancement measures for AC transmission capability, and verification test of their effectiveness using a power system simulator); multi-terminal HVDC transmission (feasibility study on multi-terminal HVDC transmission, and development and verification test of a prototype control/protection device); high performance AC/DC converter (development of a partial model for a 300 MW self-commutated converter, and field test of the developed partial model).

New methods for visualization of dynamic behavior of power systems

The present paper proposes new graphical representation methods of the dynamic behavior of power systems. Four kinds of representation methods based on computer animation techniques are proposed in this paper. These representations make it possible to visualize the results of dynamic stability, voltage stability simulations and the results of eigenvalue analysis using a personal computer. With the help of these representations, one can easily understand the dynamic characteristics of electrical power systems.

DEVELOPMENT OF A PRECISE SIMULATION PROGRAM FOR DYNAMIC ANALYSIS OF BULK POWER SYSTEM UNDER FAULTS

The authors have developed a simulation program capable of accurate analysis of a series of responses taking into full consideration the interactions between the generating plants and the transmission system during a heavy power system fault.