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"Setting a Baseline" There are, as in many fields, issues that can be popped into a few general categories. Power quality does not escape this and in this section we re-cap on what the issues are i.e. why we experience the symptoms as covered in the previous chapter. We aim to cover the question "why is x important in determining Power Quality?". Before doing this we must just reiterate that it could be more than one issue that is at play. The point of this exercise is to broadly define the areas of concern. "Voltage and Voltage Fluctuations" We begin with this most complex issue. The question "what is the correct voltage?" and proves a good place to kick off! "Feed Impedances", in other words the measure of supply 'solidity', plays a huge part in fault currents on the one extreme, and high changes in voltage as a result of changes in current (leading to 'flicker') on the other. A happy compromise would be somewhere in the middle - but what is the middle? "Leakage". The return of current to the source through routes other than the Neutral. A large number of issues are covered on this somewhat contentious subject. "Waveform Purity" deals with the more modern 'hi-tech' load where the current waveform only barely resembles a sinewave. Dealt with are the effects of this and also the concept of what happens when the waveform on the positive and negative portions of the cycle do not match. "Harmonics!" Fourier has a lot to answer for on this subject. It is generally accepted that waveform distortion can be broken up into various harmonic sinewaves of various amplitudes and phases, but this can also lead to problems. Discussed are the pros and cons to this method of working. "Imbalance" deals with both the issues of load and waveform imbalance and how high harmonics and DC components make their way onto the Neutral connection and the effect they have on components that make up the network. "Skin Effect" gets us back into the realms of reality and discusses the effects of high frequency components on an installation, and especially when to ignore such claims too! "Noise", the non-harmonic frequencies, find their way into the mains system and can, if conditions inadvertently do so, allow the noise to affect equipment to various degrees. "Intermittent Faults" are the closing subject and how such faults, in reality, are a perception and don't actually exist. Voltage And Voltage Fluctuations >>
© 17.07.02 |
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