# Clarification on AC Power Concepts in Industry

Discussion in 'General Electronics Chat' started by ElectronicGuru, Dec 1, 2014.

1. ### ElectronicGuru Thread Starter New Member

Sep 26, 2014
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I recently learned through my textbook about AC circuits, particularly the concepts of average power, reactive power, effective/RMS values, PF factor, complex power, etc.

The book started to delve into real-world applications of these concepts in industry and I'd like some clarification.

1. Why do we need reactive power in circuits in general and particularly in the power industry? What use do capacitors/inductors play?

2. When a company wants to increase its PF factor for reduced cost, one way to do so is by installing capacitors in parallel. Mathematically, I see the effect of this is to add a negative reactive power component to the total power, thus making the PF factor closer to unity (since circuits tend to be inductive in nature; see question 3). But what is the intuitive explanation for this? I've read online (but not in my book) about inductors producing reactive power and capacitors consuming it, but what does this really mean? What is the capacitor doing in the power grid that makes the average power closer to the apparent power?

2. Why is it that the power grid is favoured toward inductive loads (i.e., positive or lagging PF)? My textbook and Wikipedia simply state that it is so without providing examples.

Thanks for any help in answering these questions!

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
Interesting how conventions change. I was always of the opinion (conventional? ) that inductive loads "absorbed" reactive power while capacitive loads "supplied" reactive power - notwithstanding the fact that neither ideal inductors or capacitors absorb or supply real power.
Free spinning AC synchronous machines can be configured by excitation control to control system reactive power - sometimes referred to as synchronous condensers when "behaving" as a capacitor.

Reactive power is not "needed" in the sense that it serves any useful purpose. It is an unavoidable consequence of the nature of certain electrical loads.
The normally lagging power load (by my convention) produces negative Vars. To reduce the effective Vars at the load one has to produce positive or leading Vars which are displaced 180 degrees in phase relative to load Vars. A capacitor in parallel with the load produces leading Vars.There is either partial or complete cancelation between positive and negative Vars whilst the effective real power remains unchaged.

Irrespective of convention, the power conductors conveying real and reactive power to the load must carry the current commensurate with the effective load apparent power. Reducing the apparent power by Var cancelation reduces the current demand and hence the Joule heating losses in the overall power supply network.

Last edited: Dec 1, 2014

Mar 31, 2012
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