INTRODUCTION

Operating on tight margins and with less redundancy, power systems are sometimes just a couple of unexpected (and unlikely) contingencies away from a blackout, as the experience from the years past has repeatedly shown.  Transformation of power networks into modern structures makes them harder to protect, through addition of non-utility generators, heavy tie line transfers in a growingly competitive environment, and deployment of fast control devices. The need is great for automated systems with advanced monitoring and better real-time interfaces for operator interactions.  Advancements of measurement devices and communication technology in wide-area monitoring and controls, FACTS devices, and new procedures provide for more efficient ways to detect and control large disturbances.

System integrity protection scheme (SIPS) is a concept of using local as well as selected remote measurements and sending the necessary system information to a processing location to formulate the emergency control and protective actions for the power system.  With new technologies, more "intelligent" equipment is deployed at the local level to formulate an efficient response to ongoing disturbances.  Traditional contingency / event based remedial action systems can be made to act with proper local supervision for security.

Decentralized subsystems make local decisions based on local measurements and assorted remote information. They can send pre-processed information to higher hierarchical levels.  A major feature of the SIPS is their ability to receive remote information and commands and to send selected local information to the other locations in the system. 

Modern Protection Infrastructure     

Experience reveals similar patterns in genesis of such disturbances. Among common causes are:

• Unfavorable pre-existing conditions (i.e. generator/line maintenance)
• Tendency of cascading overloads to spontaneously develop under heavily loaded, contingency-challenged system conditions
• Inadequate VAr support
• Poor right-of-way maintenance
• Incomplete or misleading alarms
• Inability of operators to respond due to the lack of training or limitations of resources at their disposal
• Inadequate planning/operation studies
• Unavailability of automated actions to initiate appropriate response, such as automatic and pre-planned separation of the power system

While it is not practically possible to completely eliminate blackouts, with reasonable means probability of the blackouts could be substantially reduced.

Improved communication facilities and better data handling capability have greatly enhanced modern SCADA/EMS systems. Availability of critical functions of 99.99% or better is expected for reliable system operation. Alarm monitoring systems should always be in top operating condition. New alarm processing techniques should be deployed to deal with the avalanche of data during major disturbances.

Phasor measurement units (PMUs) and high bandwidth and high-speed communication networks can provide time-tagged measurements from the entire system, enabling  improved, faster and more accurate state estimators. Development of SIPS may provide for superior management of system disturbances. Those schemes are designed to operate on pre-planned, automatic corrective actions, as a result of system studies. The primary goal of  SPS schemes is to improve security of the power system.  Periodic studies should be done and protection designs reviewed to prevent misoperation. As a tradeoff between dependability and security, designers can increase the security of protection design in the areas vulnerable to blackouts. As an example, transmission line pilot protection Permissive Overreach Transfer Trip scheme (POTT), which is more secure, could be used instead of the more dependable Directional Comparison Blocking (DCB).