What is Power Factor (Rev2)

7/27/2019 What is Power Factor (Rev2)

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Power Factor


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The power factor of an AC electric power system is defined as the ratio ofthe active (true or real) power to the apparent power.

Power Factor is a measure of how efficiently electrical power is consumed.

In the ideal world Power Factor would be unity (or 1).

Unfortunately in the real world Power Factor is reduced by highlyinductive loads to 0.7 or less.

Definition


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Active (Real or True) Power (kW) = Working power, drawn by the

electrical resistance of a system performs useful work.

Reactive Power (kVAr) = Power that magnetic equipment (transformer,motor) needs to produce the magnetizing flux.

Apparent Power (kVA) = Total power provided by utility. It is the

vectorial summation ofkVAR and kW.

Power Triangle


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What causes Power Factor to

change? Inductive loads cause the AMPS to lag behind the VOLTS. The wave forms

of VOLTS and AMPS are then "out of phase" with each other.

The more out of phase they become then the lower the Power Factor.

Power Factor is usually expressed as Cos Phi. ()


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Power Factor

Analogy.


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Analogy

kVAR

kW

kVA

PF = kW

kVA

PF = kW

kW + kVAR

PF = teh

teh + buih
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Why Improve Low Power Factor?

Reactive power is one of the most significant ways that electricity is lost when it travels along

power lines.

The more reactive power that customers use, the more energy the electric system loses. This

results in the use of larger equipment on the distribution system that otherwise would be

unnecessary.

The way to reduce the amount of reactive power being lost through the system, by improving your

power factor. Improving your power factor could be beneficial to you as a customer.

Some of the benefits of improving power factor are:

Your utility bill will be smaller. Low power factor requires an increase in the generation and

transmission capacity to handle the reactive power, so improving power factor will require less

reactive power being drawn from the system. You won't be charged a reactive power fee if your power factor is above 95%

Your electrical system's branch capacity will increase. With low power factor, power losses can

occur in your distribution system, and you may even experience voltage drops. This may cause

overheating and premature failure of motors and other inductive equipment.


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Power Factor Correction

Motor running without capacitors

Without a capacitor, the motor is pulling reactive power

from the electric grid. The more this power has to travel to

reach the motor, the more it gets wasted due to lossesalong the way. This ultimately leads to a lower power

factor and higher electricity bills when the power factor is

below 95% at the facility.

On the other hand, an installed capacitor provides the

reactive power that is needed to start up and magnetize

the motor, thus eliminating the need to get it from theelectric grid. Since you'll be using less electricity from the

grid, you'll have a higher power factor and lower

electricity bills.

Motor running with capacitors


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So-called "Power Saver Devices" (known by different names) are nothing but Power Factor Correction

(PFC) devices that would connect to the mains and improve power factor measured by your electricity

meter. However it is important to note that utilities bill a residential user based on real power that does

not factor in Power factor and thus none of these devices would really reduce your monthly bill.

The so-called "Power Saving" device may be useful for industrial applications, where utilities charge the

user based on PFC rather than real power.


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Question

Can higher power factor reduce electric bill?

You are billed for real power (W), not apparent power (VA).

Residential and small commercial customers are usually billed only for

kilowatt-hours not for the reactive current that is responsible for low

power factor PF correction reduces the VA, but that is not what you are billed for.

TNB will save on distribution costs, so you may be able to negotiate

some kind of a deal with them.

No.


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What is Power Factor (Rev2)

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