Course of Action

"If you suspect there is a problem, resist the temptation to rush out and
hire a power quality recorder and to start taking measurements right away.
It pays to adopt a more systematic approach"

They say you should not believe everything you read (although, it is sincerely hoped you believe everything here!), and this was not more evident than when yours truly was featured in an article in "Electrical Review" (Pg14 - Vol 235 - No 20, to be exact). I suspect the writer got some facts muddled between what a few people said, and the article could be read as me having said that one should not use power recorders to find out what is causing the hassle.

In coming to the end of a whole section on Measurement Techniques, it would appear a rather strange contradiction if this were the case. What actually happened was a whole section of wording was left out (maybe the editor decided it was not important, how wrong he was!). My words are reprinted below, in context, for your benefit.

This particular seciton is going to deal with the 'paperwork and planning' phase of doing a power quality survey/investigation. It is a necassary step and one that should be embraced rather than shunned (and is exactly what prompted the article to be written in the first place). Following on from the article is the trap of the "7 day rule" that, although probably only relevant in the UK, is one a few salesmen have used to sell recorders but one that has also landed power quality investigators in hot water!


Before you rush out and hire that power recorder, take a look around the site. Listen to the problems, and ascertained that it may well be an electricity supply quality problem. Consider not only the equipment installed in the site, but also the location (urban or rural), the connection to the electricity supply, and the activities of the industrial neighbours.

Study when the problems occur, whether they are intermittent, happen regularly, during particular kinds of weather, and/or when an industrial neighbour does plant maintenance (using the Time-Weather Chart). This will tell when it's the best time to install a power recorder such that it captures the data when it is suspected the problems will occur.

It may be tempting to blame the electricity supplier for poor power quality. Bear in mind, however, that the majority of industrial power problems are generated internally. Ask the neighbours to the site if they suffer similar problems at the same times. If convinced that the regional electricity company is responsible, ask them to do a power quality survey at the site (and you may well want to do your own - just to see if the results match).

Now is the time to rush out and hire the recorder as the next step in solving power quality problems is to gather data by connecting up instrumentation to capture the rascal that's behind the reason you're being employed.

There are two common steps in tracing power quality issues, although the first is personally seen as a sales tactic rather than solution finding. What many are prone to do (because they were taught such) is use "immature", low-level equipment to ascertain there is something afoot. Once established they then employ the "big guns" to capture the events properly. What a waste of time....... and the client's money!!

The second step, and as far as I am concerned the only one from the start, is to use the "big gun" i.e. the fully fledged power recorder. Some will argue with this. All that can be said is they haven't done a cost study of what it takes to install equipment and then retrieve it, twice! When there are available extremely simple pieces of kit to operate, it just makes no sense to do a job more than once. Such pieces of equipment are also available for hire at very reasonable rates thus alleviating purchasing costs for the "one off" requirement.

The main aim here is to gather all the information regarding every aspect of the site's power. From here, once you have collected and analysed all the data (using the next section, "Interpreting the Readings", to help you do this), one can now switch to a single-phase device to help pinpoint the trouble.

However, before totally throwing "step one" to the wind, it is acknowledged that there are times when elements of doubt are cast as to the validity of a complaint. If genuine helpful data can be obtained by the use of devices such as "plug-in" recorders then by all means use them. Many large electricity supply companies use this approach as they are then 'seen' to be attending to a client's complaint within a prescribed period (the sales tactic referred to earlier). This also alleviates the need to send skilled people to site for the first visit.

There is one danger with using this approach being the customer, if they are paying for the service, doesn't see you doing anything for their money. Personally, when parting with hard earned cash, seeing effort being used in the gaining of results counts for a lot.

There is one advantage to the low-level recorder making its way to site ahead of your visit. It can act as an indicator as to the extent and frequency of the offending power issue. When arriving on site with the power recorder, a quick analysis of the low-level unit could very well give an indication of the area of concern and the period the proper recorder will have to remain on site. Be forewarned, don't let the low-level unit steer your thinking. Let the big bun tell you what's really going on before making any rash decisions.

Furthermore, if carefully planned, remote access of the power recorder could be possible thus allowing daily viewing of any possible disturbances with a view to minimising the time the equipment needs to stay on site. Care should be exercised, however, as this could result in time wasted rather than constructively used. The time spent analysing a day's data for the one site could be spent analysing a week's data from another. Effectively this means you could be earning 5-7 times as much, kind of makes economic sense!

Yes, there are going to be the jobs where two trips to site will be required, the first to merely connect up the recorder. Some institutions will not allow "open conductor" work on main incoming feeders for fear of losing power through accidents. They are (apparently) in no way concerned about your well-being but rather the financial loss if their computer systems die. A good example of this is financial computer centres. If you are given permission to operate "live", please have the relevant authorization and certification as well as reading the chapter on safety ahead of time.

"The final stage of the process is:
to ensure the data is collected in its entirety!"

All too often databases are sent through and there is something missing..... all because it was deemed unnecessary by the person downloading the data from whichever instrument. Even if data is known to be irrelevant to the survey/investigation in question, it should still be downloaded and retained for future use. With surveys, the importance of retaining information is even more critical as such information may prove relevant when comparing data at a future date.

Analyse the data (or hire a consultant to do so). The section on "Solutions" is dedicated to this. Then decide what action to take. Surge and impulse protection equipment and uninterruptible power supplies are becoming common ways to tackle power quality problems, although it must be stressed that there is no single solution. Transient protection and passive or active harmonic filters are also popular. However, it is important to remember that there may be simpler solutions. For example, if your site suffers from harmonics, it may be possible to stagger processes without affecting production, and reduce or limit the problem.

A follow-up survey will establish that the measures you have taken have been effective.

Having confirmed that you have solved your problems, it is worth considering a permanent recording installation to ensure that changes in plant and equipment do not compromise power quality. Again, this need not be a complex or expensive option. For example, if you have established that your site is vulnerable to harmonics, it may be sufficient to fit a device capable of the recording the basics and harmonics only.

The 7-Day Rule  >>

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