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What is “pu” in electrical engineering?

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admin    14

What is “pu” in electrical engineering?
Pu stands for per unit and this will be used in single line diagram of power distribution and it is like a huge electrical circuit with no of components (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of the component is considered as base values, then all other component ratings will get back into this basis.Those values are called as pu values. (p.u=actual value/base value).

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DrD    1

Per Unit (p.u.) is simply a normalization that is very popular in electrical circles. The principal merit of the per unit system, as explained to me by Prof. Thomas Whitaker of the University of Houston, is that when expressed in per unit, many parameter values fall into fairly narrow ranges. This makes it easier to estimate, for example, the mass moment of inertia of a generator rotor for a machine that is not fully designed as yet. This in terms can facilitate system stability studies and similar thing.

The down side to per unit (and this is a big thing, in my opinion) is that you never speak in terms of actual numbers, but only in terms of ratios. Thus if the power is 0.8 pu, the machine is not up to full power, but we also have no idea what the actual power is. In my thinking, much of it comes down to this question: "Do you want actual numbers, or do you simply want ratios?"

DrD

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