Power system restoration, as an extraordinary mode of system operation, requires careful planning and operator training. The generic tasks of restoration include determination of system and equipment status, preparation of plants and network for systematic restoration, reenergization of the network, and system rebuilding. The procedures for developing an effective restoration plan include formation of a qualified planning team, review of relevant system characteristics, formulation of assumptions regarding blackout scenarios, agreement on restoration goals, development of strategy and tactics, validation of the plan, training, and documentation. >

Power system restoration planning

Special protection schemes are those designed to detect one or more predetermined system conditions that have a high probability of causing unusual stress on the power system, and for which preplanned remedial action is considered necessary The failure of these schemes to accurately detect the defined conditions, or their failure to carry out the required preplanned remedial action, can lead to very serious and costly power system disturbances It is natural, therefore, that a concern for the reliability of these schemes has been expressed This paper reports on a joint IEEE-CIGRE survey to determine the experience with special protection schemes, and to question the designers and operators of these schemes regarding the reliability of performance Questions were also directed to the design process itself, the reliability criteria used for the design, and the analytical methods used to assure reliability in the design

Industry experience with special protection schemes

The application of microprocessor-based phasor measurements to novel adaptive protection schemes is presented. The concepts of digital adaptive protection in which relay characteristics are modified in response to external signals and conditions in the system, are examined. The importance of real-time phasor measurements in adaptive protection systems is illustrated by two examples. The first involves obtaining synchronizing information about phasor measurements to be used for current differential protection of a multithermal line. By estimating the reference angles for the phasor measurements the effect of synchronized sampling can be obtained without the expense of synchronizing equipment. The second use is the adaptive setting of out-of-step blocking and tripping. Traditional approaches experience problems because the settings are, of necessity, compromises based on offline studies. By reacting to real-time phasor measurements from selected buses in interconnection, it is shown that improved out-of-step blocking and tripping is possible. >

Some applications of phasor measurements to adaptive protection

Although a major power failure is a complex unique problem, certain common guidelines for power system restoration have emerged from previous papers. This article is a review and organized compilation of those papers. As such, it provides a framework to help power system operators limit the extent of major power failures, and if a failure occurs, to help operators rebuild a stable electric power system and restore unserved load as safely, smoothly and quickly as possible with minimal adverse impact to the public. These guidelines also offer recommendations to help prepare for a major power failure in advance, thereby further facilitating restoration. >

A framework for power system restoration following a major power failure

A recently developed predictive out-of-step protection system is described. The purpose of this protection system is to prevent total system collapse caused by step-out between large-capacity generator groups due to a serious fault in the trunk transmission line. This is accomplished by using online data collected during the incubation phase to predict a step-out and then issuing a system-seperation command. The system has the following characteristics: (1) the phase difference between several large generator groups is measured from online voltage data collected from substation busbars in the vicinity of the generators at a sampling rate of 600 Hz: (2) the phase difference at 200 ms in the future is predicted from the measured phase-difference data; and (3) if the predicted phase difference exceeds the instability threshold value, system separation if performed taking into account the power supply and demand balance after tripping. >

A predictive out-of-step protection system based on observation of the phase difference between substations

This paper proposes a new algorithm for an emergency control system which prevents transient instability by generator tripping. The algorithm is based on the energy function method, and it precisely can determine the amount of generation to be tripped. A prototype of the proposed system has been made, and it has been confirmed that the algorithm has been easily implemented in a micro-computer. Furthermore, test results show that the algorithm works well in an ATL (Artificial Transmission Line) System. This paper describes theoretical aspects of the algorithm, implementation and test results.

Development of a Generator Tripping System for Transient Stability Augmentation Based on the Energy Function Method

This paper deals with overvoltages caused by self-excitation in a separated power system, which has some generators, heavy load and large shunt capacitance of underground cables and/or shunt capacitors. The condition of stability in a separated power system is analyzed and a comparison with the experimental result is presented.

Analysis of Overvoltages Caused by Self-Excitation in a Separated Power System with Heavy Load and Large Shunt Capacitance

This paper proposes a new digital protection scheme for shunt reactors. The method proposed here is based on the relationship between flux and current of shunt reactors and simulation results indicate that this type of relay is less affected by inrush phenomena than conventional impedance relays. The selection of cutoff frequency of Low Pass Filter (LPF), sampling interval and integral time is also discussed and their desirable values are estimated from the sensitivity analysis of these parameters.

S. Nishida

Papers

Development of a Generator Tripping System for Transient Stability Augmentation Based on the Energy Function Method

Analysis of Overvoltages Caused by Self-Excitation in a Separated Power System with Heavy Load and Large Shunt Capacitance

A New Algorithm Of Digital Protection For Shunt Reactors