Existing protection/control systems may be improved and new protection/control systems may be developed to better adapt to prevailing system conditions during system-wide disturbance. While improvements in the existing systems are mostly achieved through advancement in local measurements and development of better algorithms, improvements in new systems are based on remote communications.
However, even if communication links exist, conventional systems that utilize only local information may still need improvement since they are supposed to serve as fallback positions. The increased functions and communication ability in today’s SCADA systems provide the opportunity for an intelligent and adaptive control and protection system for system-wide disturbance. This, in turn, can make possible full utilization of the network, which will be less vulnerable to a major disturbance.
Out-of-step relays have to be fast and reliable. The present technology of out-of-step tripping or blocking distance relays is not capable of fully dealing with the control and protection requirements of power systems. Central to the development effort of an out-of-step protection system is the investigation of the multi-area out-of-step situation. The new generation of out-of-step relays has to utilize more measurements, both local and remote, and has to produce more outputs. The structure of the overall relaying system has to be distributed and coordinated through a central control. In order for the relaying system to manage complexity, most of the decisions have to be made locally. Preferably, the relay system is adaptive, in order to cope with system changes. To deal with out-of-step prediction, it is necessary to start with a system-wide approach, find out what sets of information are crucial and how to the process information with acceptable speed and accuracy.
Protection against voltage instability should also be addressed as a part of hierarchical structure. The sound approach for designing the new generation of voltage instability protection is to first design a voltage instability relay with only local signals. The limitations of local signals should be identified in order to be in a position to select appropriate communicated signals. However, a minimum set of communicated signals should always be known in order to design reliable protection, which requires the following: (a) determining the algorithm for gradual reduction of the number of necessary measurement sites with minimum loss of information necessary for voltage stability monitoring, analysis, and control; (b) development of methods (i.e., sensitivity analysis), which should operate concurrent with any existing local protection techniques, and possessing superior performance, both in terms of security and dependability.
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