Good is good enough?!

Author: Marco C. Janssen

In general language redundancy refers to things being duplicated without adding value. This can be in presenting an idea using more information than is necessary for one to be able to understand the idea or an unnecessary or unessential repetition of meaning, using different and dissimilar words that effectively say the same thing twice, or it is the use of more words or word-parts than is necessary for clear expression.
or
It can be an excessive flow of words (such as the previous phrase).

In engineering however redundancy is used to describe the duplication of critical components of a system with the intention of increasing reliability of the system. This is usually achieved by installing a backup or fail-safe.

But is redundancy always necessary or even better?

In many safety-critical systems, such as fly-by-wire and hydraulic systems in aircrafts, some parts of the control system may be triplicated. An error in one component may then be out-voted by the other two. In a triply redundant system, the system has three sub components, all three of which must fail before the system fails. Since each one rarely fails, and the sub components are expected to fail independently, the probability of all three failing is calculated to be extremely small. But this kind of solution comes at a price and in modern economics a cost benefit calculation is often used to evaluate the risk (cause x effect) before final decisions are taken on how redundancy is going to be applied.

In modern systems redundancy can come in many forms such as hardware redundancy, information redundancy, time redundancy and software redundancy or a combination of these. In order to determine what level of redundancy is required, one should be able to calculate the probability of system failure and analyze risk resolution. The main question is how to do that in systems that are increasingly complex and use several new solutions of which the characteristic (failure) behavior is yet to be determined?

As we gained more experience in the power industry with traditional /conventional systems concepts that were developed for the duplication of protection systems, creating fail safe mechanisms, etc., many people argue that we should use these principles in modern systems also. I have seen examples however where people in their search for reliable system have started to duplicate components in modern substation automation systems without looking at the overall consequences. This resulted in some cases in systems that became so complex that an analysis of the probability of failure becomes difficult, if not impossible.

A side effect also is that the systems become more expensive but also increasingly difficult to maintain and operate.
Or,
in other words we may have duplicated things without really adding value.

I therefore think that we need to take one step back and look at the real need for redundancy within our systems. In many cases I believe that the Keep It Simple principle can provide a sanity check that allows us to focus on the really mission critical elements of our systems and evaluate the risk associated with the failure of these elements.

Another thing to consider is the definition of the requirements for Reliability, Availability, Maintainability and Performance for each element and for the entire system so that we have something to evaluate our systems against.

Finally I believe that we need to start developing new rules and principles for the definition and evaluation of our systems in combination with new concepts to guarantee a fail safe operation of mission critical systems.

These new concepts should focus on making use of the means technology provides to us now instead of trying to re-apply the concepts and solutions of the systems of the 20th century. This would be like trying to apply the safety check procedure designed for the DC2 aircraft to check the highly advanced systems of an Airbus 380.

In my opinion we should aim for systems that have an increased functionality, that add value to the operation of the utility:

  • that are fail safe
  • that are cheap
  • that are easy to use
               and above all
  • that are simple...

This should provide an interesting challenge for us engineers since these requirements contain multiple contradictions in themselves. I therefore look forward to seeing solutions being presented and built that achieve all of these requirements within one single solution.

The good thing is that it will force our community to think outside of the traditional paths and come up with creative and new solutions.

And remember… 

Don't look at the way things are and ask why.  

Think about the way things could be and ask why not?

 

 

Marco C. Janssen graduated the Polytechnic in Arnhem, The Netherlands and developed further his professional skills through programs and training courses. He is President and Chief Commercial Officer of UTInnovation LLC - a company that provides consulting and training services in the areas of protection, control, substation automation and data acquisition, and support on the new international standard IEC 61850, advanced metering and power quality. He is a member of WG 10, 17, 18, and 19 of IEC TC57, the IEEE-PES and the UCA International Users Group.

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