Measurement Techniques

"Power Quality - the science applied when standard electrical methods are unsuccessful at investigating and mitigating the damaging effects of a poor electrical supply, and/or improving the quality of the supplied power"

This is likely to be the most easily understood aspect of Power Quality, but is also the most important! Without correct measurement there is just no way anyone can judge whether it was or not a power issue that caused the problem - let alone the extent of the cause.

But herein lies a crunch. The more this aspect is discussed with facilities managers of data centres the more it is realized that, generally, they don't care about power quality. That's right, they are not concerned about the quality of the very energy that drives the racks and racks of servers, switches, and other peripherals. How much they use; Yes. What is the quality; You've got to be joking!

To show the extent of their dismissive attitude, one character from a major credit card data centre even referred to those who concern themselves with promoting the importance of power quality as fools! Well, this fool has two questions. Does his chairman of the board know his attitude? And do you, a credit card holder, realize the danger behind such an attitude? They all yell out about their fantastic customer focus, but it appears to be no more than a pack of lies!

If there was a concern about power quality, and knowing the extent of the causes, then the suppliers of power quality instrumentation would be crying under the strain to supply monitors fast enough. This is not happening. It's not even close! There is this misconception that once an event has occured, one can simply hire a piece of suitable kit and then determine what the problem was. Power does not work that way. Once used, it's gone. And what came with it (spikes, etc.), disappeared with it too.

Knowing about symptoms and understanding the causes is only part of the solution. At the other extreme is the interpreting of the readings. Measurement is the bridge between these two and provides a means to gain knowledge of the extent of the causes behind any power quality issues. This section deals with the requirements and techniques to achieve this knowledge.

Don't lose sight of the ultimate aim which is to ensure that once you have left the site you will be able to provide feedback as to what fault, if any, is present at the site. Far too often the aim of the power quality investigator is only to ensure the supply is "within spec". Two reasons for this have become apparent. The first is limited time and a high workload. The second, and one not often admitted, is a lack of knowledge on the part of the power quality investigator.

This lack of knowledge has distinctly led to power quality monitoring being ignored in areas where it is of paramount importance. While it is advocated that more monitoring is done, it needs to be ensured that it is not over emphasized. It, with other paramaters that need monitoring, deserves a rightful place. It must form part of a whole approach to quality and reliability.

Using the two previous sections, Symptoms and Causes, to provide a knowledge base, the next section on how to Interpret the Readings, and this section where we deal with what is available to the power quality investigator as well as how to use it, hopefully I can achieve my aim of combatting any ignorance that may prevail on the subject.

A word of warning before we go an further. If the previous two sections have 'done your head in', then you must stop right here and go back and learn your basics, and I'm referring to basic electronics! Power Quality as a subject is not for those who don't have the basics, and you will only prove to be a danger to yourself and others around you if you haven't a solid foundation in the basics.

If you are one of those just mentioned, and are in any way involved in ensuring the quality of power supplying sensitive electronic gear, then you will need to pluck up enough courage to hand in your resignation (before they fire you through incompetence) or, better still, a request to go and learn what you should have known in the first place.

Then, when armed with the required basic knowledge, you come back, learn the finer points of power quality, and acquire the appropriate gear. Please do note I state 'appropriate gear'! There are so many people running around with all sorts of unsuitable stuff (the poor souls have probably been conned by some unsuitable sales tactic!).

Here I promise to separate out technical truth from questionable sales talk.

Before one even starts trying to measure anything; The one most critical part of successful measurement is being able to talk about it afterwards. Adopt a safe working practice eliminating both injury and fatality. In fact, as this is so important, a whole section has been devoted to it. But who reads safety guidelines? I've yet to meet one, probably because they're dead!

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© 29.10.02