Splitting strategies for islanding operation of large-scale power systems using OBDD-based methods

Splitting strategies for islanding operation of large-scale power systems using OBDD-based methods

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912 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 18, NO. 2, MAY 2003 Splitting Strategies for Islanding Operation of Large-Scale Power Systems Using OBDD-Based Methods Kai Sun, Da-Zhong Zheng, and Qiang Lu , Fellow, IEEE Abstract— System splitting problem (SS problem) is to de- termine proper splitting points (or called splitting strategies) to split the entire interconnected transmission network into islands ensuring generation/load balance and satisfaction of transmis- sion capacity constraints when islanding operation of system is unavoidable. For a large-scale power system, its SS problem is very complicated in general because a combinatorial explosion of strategy space happens. This paper mainly studies how to find proper splitting strategies of large-scale power systems using an OBDD-based three-phase method. Then, a time-based layered structure of the problem solving process is introduced to make this method more practical. Simulation results on IEEE 30- and 118-bus networks show that by this method, proper splitting strategies can be given quickly. Further analyses indicate that this method is effective for larger-scale power systems. Index Terms— Graph theory, islanding operation, ordered bi- nary decision diagrams, power system protection, splitting strate- gies, system splitting. I. INTRODUCTION F OR a power system, some serious disturbances may trigger growing oscillations, which lead to loss of synchroniza- tion between groups of generators and possibly blackouts. Nor- mally system islanding may automatically happen after some transmission lines are tripped by local relays, but unbalanced electrical islands are often produced. Thus proper load shed- ding and generator tripping must be performed simultaneously. Fatally, if automatic system islanding only by local relays pro- duces islands with excessive electrical unbalance (e.g., some is- lands are mainly made up of generators and, by contraries, the others almost have no generator but loads, then blackout of the entire system is almost inevitable). System splitting, also known as controlled system separation, is that dispatching center ac- tively split the whole transmission network into two or several islands by tripping properly selected lines. After system split- ting, the whole power system is under intentional islanding op- eration and each island of load and generation theoretically re- mains in balance. Thus, “although the power system is oper- ating in an abnormal degraded state, customers are continuing to be served” [7]. The studies of historic blackouts or outages Manuscript received September 28, 2002. This work was supported in part by NSFC under Grants 60074012 and 60274011 and in part by the National Fun- damental Research Funds under Grant G1998020310 and Tsinghua University project. The authors are with the Center for Intelligent and Networked Systems, De-
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Splitting strategies for islanding operation of large-scale power systems using OBDD-based methods

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