Computers in the Developmentof - IEEE Xplore

PSE&G created custom ASC programs for all of the security analysis functions. The ASC language allows the user to preprogram sequences of instructions to the security software so that operators only need to enter information specific to a particular study. Having this flexibility allowed PSE&G to fit the operation of the security software to meet special needs of its operations personnel. The security analysis software and additional hardware have been successfully integrated into the existing PSE&G energy control center. Future plans call for adapting the software to operate as an operator training simulator in which the security analysis load flow model provides a model of the system which responds to the

load flow mode would have been very inefficient and time con¬ In addition to conserving time, the ILF provided a better understandina of the restoration process.

suming.

POWER SYSTEM MODELING

trainee's actions.

January 1982, p. 43

Role of Interactive and Control Computers in the Development of a System Restoration Plan R. J. Kafka, D. R. Penders, and S. H. Bouchey Potomac Electric Power Co., Washington, DC M. M. Adibi IRD Corporation, Bethesda, MD The duration of power system disturbances can be minimized by executing a well developed and maintained system restoration plan (SRP). Such a plan is significantly improved when the efforts of the operating personnel and systems analysts are combined. The team effort is enhanced by concurrent use of control computer and interactive computer systems especiaHy when both groups and both systems are located in an operating environment. At Potomac Electric Power Company (PEPCo) the above procedure was adopted to achieve an efficient solution to SRP. It was concluded that the approach and results of this development effort were extremely beneficial to PEPCo and should be of value to other utilities. System restoration following a major disturbance is a difficult task complicated by a number of factors including (a) the unfamiliarity of the system operators with the outage situation and pressure of time; (b) the possibility of voltage collapse due to reactive power im¬ balance; (c) the risk of frequency excursions due to load and generation mismatch; and {d) the need for precise scheduling of thermal units' restart, loading, and coordination with load pick-ups. Therefore, a carefully prepared, current, readily accessible and easily understood SRP is necessary for an efficient and orderly recovery from a total or partial system collapse. In order to develop an SRP, it was necessary to model the steady state behavior of the PEPCo power system by representing the physical and operational data in an interactive computing system. The model then had to be validated against the measured and telemetered operating data obtained from the control computer system. After validating the model, the project team formulated a strategy for system restoration. The strategy consisted of sec¬ tional ization of the power system into a number of subsystems in accordance with a set of guidelines established by the operating personnel. A restoration plan for each subsystem was thus de¬ veloped by simulating a step-by-step integration of loads and generation. The objectives were to restore and to synchronize the subsystems simultaneously. This iterative procedure entailed careful consideration of the probable effects of each restoration step on the rest of the system and on the subsequent measures. The process was facilitated through the intensive use of interactive load flow (ILF) program. An outline of the iterative process involved is

shown below. The control computer system had two roles. First, it provided system operating data for verification of interactive load flow solutions, and second, it guided the project team in the development of an efficient SRP for execution through its man-machine interface, data acquisition, and remote control capabilities. The interactive computing system also had two roles: first, during modeling and model validation, and second, during reconstruction of the power system. In both areas, solutions to a very large number of load flow cases were required. To enter and run so many cases in the batch

PER JAN

VALIDATION OF MODEL

ESTABLISHMENT OF GUIDELINES

DEVELOPMENT OF STRATEGY

SECTIONALIZATION AND SIMULATION OF RESTORATION

PREPARATION OF DETAILED INSTRUCTIONS

Three programs are required in the effective development of a SRP: an interactive load flow, a long-term dynamic simulator and a critical path method. The ILF is an excellent tool for evaluating quasi steady-state transmission line loadings, reactive power balance, generator loadings, transformer tap positions, shunt capacitor and shunt reactor status, and phase angles between load centers and generating stations. The dynamic simulator is needed for most effective evaluation of mismatch between load pick-up and gen¬ erator responses, the change in system frequency, the effect of feeders equipped with under frequency relays, and the rate at which generators could be loaded. In the absence of an adequate dynamic

simulator, operating practices and guidelines were used. Finally, the critical path method can be applied to the development of the SRP to schedule generator restart and loading with switching operations and to coordinate critical time intervals such as maximum and minimum elapsed times for hot restart and cold restart of steam units. Manual scheduling methods were used during this initial SRP effort. The operator-analyst team effort and the on-line/off-line com¬ puter applications in an operating environment produced an SRP for light- and peak-load conditions which were acceptable to the system operators. This is the most significant result of the project. In the course of SRP development a number of difficulties were exper¬ ienced which are presently under consideration by PEPCo and whose solutions would provide additional flexibility in system restoration. Possible solutions include development of generation isolation schemes, installation of shunt reactors, synchronization facilities, and system frequency telemetering. The SRP effort also indicated the need for more accurate determination of prime movers frequency response to sudden changes in loads. This report presents application of available analytical tools in¬ cluding interactive load flow programs in the development of a system restoration plan. The need for development of a dynamic simulator is recognized and its application defined. 21