I learned from a professor in engineering school that engineers are trained to do one thing: Solve problems. I have always agreed with that viewpoint, but I have also come to understand that problems are best solved with a system approach. This understanding took some time to develop. As with any new engineer, my initial perspective on problem solving was fairly narrow. Starting out as a field engineer in the power industry, it didn't take long to broaden my viewpoint with some real-world experience. I quickly gained an appreciation for power-system performance in field conditions. Next I spent some time as a project engineer, which enhanced my view in regard to system design and construction. These two positions taught me a great deal, but they tended to keep me running from one project to the next, looking for the quickest way to get the job done. It wasn't until a later position in distribution planning when things clicked. I could see I'd been a bit shortsighted on earlier projects and hadn't been looking at the whole picture. It was then I realized the value of using a system approach, and I've been using it ever since.
The system approach definitely applies to power quality and reliability problems. They are best addressed by reviewing the overall electrical system. There is a multitude of ways to mitigate power quality problems and increase customer reliability. If you focus exclusively on the problem area, or end-use equipment, you might miss the best source-side solution. This is especially true when considering power reliability. Typically, when electric disturbances occur, end-users call their utility to help identify the source of the problem. Once that determination is made, it becomes either a utility problem or customer problem. Too many times the type of solution is limited because of where it occurred and who owns the system. Even within the same system (utility or customer), the solution can be further constrained because of inconsistent design philosophies and construction practices.
Let's consider some scenarios where various system improvements could be entertained: 1) an industrial plant with a backup switchgear and transformer served from a single underground circuit, 2) UPS systems that serve only some of the industrial process controllers needed to ride through a voltage sag, 3) a commercial development with underground loop-feed utility service served from the same overhead distribution feeder, and 4) businesses with LAN UPSs and no service-entrance surge protection. These situations might represent cognitive engineering decisions where the risks have been assessed and customers understand their protection is limited. But more times than not, the risks have not been recognized, reconciled, or quantified. When that is the case, you end up with piecemeal solutions that don't optimize the system or deliver the best bang for the buck.
Experienced engineers understand they should evaluate all the sources of trouble for the system in question. This sounds like engineering 101, but our own familiarities and paradigms tend to limit where we look for a solution. Common sense dictates trying the quick and economical fix first. But tried and proven measures can be a costly crutch. Remember, the majority of premise-related PQ problems are wiring and grounding. These are usually low-cost fixes that don't require additional equipment or devices. Also realize if you don't consider the system impact, some actions may remedy one problem but create another, compromising the system's overall reliability.
Make sure you look outside your known system or area of responsibility for a better solution. Utilities and businesses need to work together and share information so the best decisions are made. The design and performance history of your electric system should be known before you implement corrective measures. After you have identified the problem and are ready to act, perform an assessment that starts upstream at the utility source then drills down to the affected end-use equipment. If a system improvement is needed, including redundant sources, better voltage regulation, or transient protection, ascertain the best place to perform the improvement. Even if budgets won't allow the optimum solution, the system approach to reliability will ensure a better understanding of the system's limitations. This in turn helps match your reliability risk with the best solution available.
Philip Musser, Editor-in-Chief
[email protected]
www.powerquality.com
