27-02-2012, 06:00 PM
04-06-2012, 12:06 PM
Trends in Power System Protection and Control Trends in Power System Protection and Control.pdf (Size: 98.22 KB / Downloads: 131) Abstract As a consequence of deregulation, competition, and problems in securing capital outlays for expansion of the infrastructure, modern power systems are operating at ever-smaller capacity and stability margins. Traditional entities involved in securing adequate protection and control for the system may soon become inadequate, and the emergence of the new participants (non-utility generation, transmission, and distribution companies) requires coordinated approach and careful coordination of the new operating conditions. Introduction System-wide disturbances in power systems are a challenging problem for the utility industry because of the large scale and the complexity of the power system. When a major power system disturbance occurs, protection and control actions are required to stop the power system degradation, restore the system to a normal state, and minimize the impact of the disturbance. The present control actions are not designed for a fast-developing disturbance and may be too slow. Angular stability The objective of out-of-step protection as it is applied to generators and systems, is to eliminate the possibility of damage to generators as a result of an out-of-step condition. In the case of the power system separation is imminent, it should take place along boundaries which will form islands with matching load and generation. Distance relays are often used to provide an out-of-step protection function, whereby they are called upon to provide blocking or tripping signals upon detecting an out-of-step condition. The most common predictive scheme to combat loss of synchronism is the Equal-Area Criterion and its variations. This method assumes that the power system behaves like a two-machine model where one area oscillates against the rest of the system. Whenever the underlying assumption holds true, the method has potential for fast detection. Voltage stability Voltage stability is defined by the System Dynamic Performance Subcommittee of the IEEE Power System Engineering Committee [3] as being the ability of a system to maintain voltage such that when load admittance is increased, load power will increase, and so that both power and voltage are controllable. Also, voltage collapse is defined as being the process by which voltage instability leads to a very low voltage profile in a significant part of the system. Possible Improvements in Control and Protection 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, systems with only local information may still need improvement since they are envisioned as fallback positions. |
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