Anonymous
Anonymous asked in Science & MathematicsEngineering · 7 years ago

# why we dont increase the PF(power factor to 1?we always keep it 0.85 is there any effect related to resonance?

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• 7 years ago

I assume you're referring to power factor in the operation of power systems. In a power system the load is the customer and the power plant is the provider. The load (customer) usually demands power at a power factor of <1. This is typically because it has equipment which needs to be magnetised as well as consuming real power. So the power plant and the supply equipment must supply both real and reactive power. The loads could (theoretically) and to an extent they are, compensated to minimise the reactive power demand but the latter cannot realistically be eliminated.

The provider's equipment must therefore be dimensioned and rated to provide not only the real but also the reactive power and very often the rated power factor of installed equipment is as you say, 0.85. But this is a capability and a number on the nameplate. It only expresses a limit, not an operating number. Nobody keeps the operative power factor at that number. The actual power factor during operation is not obliged to be at that value and effort is always being made to run at higher power factors. However the capability must be there and may sometimes be needed to provide flexibility in operation and in the end to best serve customers.

• Bob
Lv 7
7 years ago

What Bramble states is correct but he has not got to the really important issues.

2 reasons,

1/ to get to unity pf requires a disproportionate amount of extra capacitors, it's just not worth the extra and large cost, 0.95 lagging is considered very good.

2/ achieving unity pf also achieves resonance. In the parallel circuit of the inductor and capacitor at resonance, large currents will be passed between the capacitor and inductors, this will overheat motor windings, cables and cause protective devices such as circuit breakers and fuses to operate.

Reonance in a parallel AC power circuit is to be avoided. Your suggestion to resonance is correct.

Source(s): HND Electronics UK, used to teach this stuff