by Alex Apostolov, Editor-in-Chief

System Integrity Protection Schemes (SIPS) - What are they, and Why do we need them?

As we have discussed in regards to many topics covered in the PAC World magazine, our industry is going through a period of significant changes due to the wide spread penetration of distributed energy resources with different behavior compared to the conventional synchronous machines, operating the system close to its stability limits, as well as the latest developments in computer and communications technology.

These changes require a fresh look at what the protection, automation and control industry is doing to ensure power system security. We are not talking about the ability of the system to withstand cyber security attacks. We are talking about the ability of the electric power system to withstand contingencies without significant impact on customers and the stability of the system.

For many people the control of the electric power system is the job of the system operators, based on the data available from remote terminal units (RTUs) located in substations around the system and polled by the SCADA system maybe every second.

This data then may be used for state estimation and to help the system operator make a decision if some action needs to be taken to maintain the stable operation of the system. And this is the case in relatively advanced systems.

Many people may feel comfortable, since a human being is taking care of this task and human beings are at the top of the evolutionary chain. So, we are in good hands and there is nothing to worry about.
Another reassuring factor is the knowledge that the system is designed to withstand N-1 conditions.

Unfortunately, none of the above helps during disturbances. As we have learned from the analysis of many blackouts around the world, they are never the result of a single contingency. There are usually a sequence of events that lead to the gradual deterioration of the state of the electric power system until a single event triggers the fast-developing final stage and a system collapse.

In conventional SCADA systems the level of deterioration may not be obvious to the system operator and once the final stage is reached, it is impossible for a human being to react fast enough to prevent the system collapse.

This is where SIPS - the (System Integrity Protection Schemes) come into play. First we need to understand that they may be called different names. In the past they were Emergency Control Systems. Then they became Remedial Action Schemes (RAS), later Special Protection Schemes (SPS) and finally – SIPS.

However, it is not that important what we call them. It is much more important to know what they are, how to design them, how to apply them and how to test them. None of this is simple and all of them require a good understanding of the electric power system, the possible contingencies, the available technologies, engineering process and testing methods and tools.

That is why this issue of the magazine is dedicated to SIPS in an effort to answer the questions mentioned in the title above, and to provide information about key resources that can help PAC engineers take some actions to meet the challenges of today’s electric power systems.

"Action springs not from thought, but from a readiness for responsibility."

G. M. Trevelyan

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