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PRESENTATION ON

POWER FACTOR

MANAGEMENT

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Power Factor

The power factor of an AC electric power system is defined as the ratio ofthe realPower flowing to the load over the apparent power in thecircuit, and is a dimensionless number between 0 and 1 .

Power Factor Definition : Power factor is the ratio between the KW and

the KVA drawn by an electrical load where the KW is the actual loadpower and the KVA is the apparent load power.

It is a measure of how effectively the current is being converted intouseful work output and more particularly is a good indicator of theeffect of the load current on the efficiency of the supply system.

Real Power is the capacity of the circuit for performing work in a particulartime.

Apparent power is the product of the current and voltage of the circuit.

Due to energy stored in the load and returned to the source, or due to anon-linear load that distorts the wave shape of the current drawn from thesource, the apparent power will be greater than the real power.

http://en.wikipedia.org/wiki/AC_powerhttp://en.wikipedia.org/wiki/AC_power

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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 phasethey become then the lower the Power Factor. Power

Factor is usually expressed as Cos Phi. ()

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Effect of poor Power factor

In an electric power system, a load with a low power factor drawsmore current than a load with a high power factor for the sameamount of useful power transferred.

The higher currents increase the energy lost in the distributionsystem, and require larger size of wires and other equipment.Because of the costs of larger equipment and wasted energy,electrical utilities will usually charge a higher cost to industrial orcommercial customers where there is a low power factor.

Linear loads with low power factor (such as induction motors) can becorrected with a passive network of capacitors or Inductors . Non-linear loads, such as rectifiers , distort the current drawn from thesystem. In such cases, active or passive power factor correction

may be used to counter the distortion and raise the power factor. The devices for correction of the power factor may be at a central

substation, spread out over a distribution system, or built into power-consuming loads.

http://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Induction_motor

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Importance of power factor in distribution

systems

The significance of power factor lies in the fact that utility companies supplycustomers with volt-amperes, but bill them forwatts. Power factors below 1.0 requirea utility to generate more than the minimum volt-amperes necessary to supply thereal power (watts). This increases generation and transmission costs.

For example, if the load power factor were as low as 0.7, the apparent power would

be 1.4 times the real power used by the load. Line current in the circuit would also be1.4 times the current required at 1.0 power factor, so the losses in the circuit wouldbe doubled (since they are proportional to the square of the current). Alternatively allcomponents of the system such as generators, conductors, transformers, andswitchgear would be increased in size (and cost) to carry the extra current.

Utilities typically charge additional costs to customers who have a power factor belowsome limit, which is typically 0.9 to 0.95. Engineers are often interested in the powerfactor of a load as one of the factors that affect the efficiency of power transmission.

With the rising cost of energy and concerns over the efficient delivery of power, activePFC has become more common in consumer electronics

http://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Volt-ampere

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How to reduce bill ?

If large industrial customers place inductive loads on the power grid,the utility company installs special electric meters to measure this.The electric company then charges them a fee. The industrialcustomer must pay for the energy losses they cause in the warmpower lines.

There is a way for industrial customers to fix the problem. There is away to correct the power factor and bring it to 100%. If the customeris using an inductive load, they can place just the right value ofcapacitor across that load. The energy then stops reflecting back tothe electric company generators. No longer do the power lines sufferexcess heating. The electric company measures this, then stops

charging the extra fee. (Actually the energy still reflects back andforth between the inductive load and the added capacitor. Theexcess heating in those short local wires is insignificant.)

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How much energy can be saved byinstalling correction Capacitors

Power factor correction does not save much energy usually lessthan 1 percent of load requirements but even that benefit dependsupon how low the power factor is to begin with and how heavilyloaded are in-plant distribution system conductors. Note that powersupplied to your motor driven-equipment is proportional to Volts

Amps. Energy losses in your in-plant distribution system coincide

with your voltage drop. If your transformer supplies power at 480volts and the voltage at your motor terminals is 470 volts, you havea voltage drop of 10 volts, or approximately 2 percent of 480 volts.The total power loss in the in-plant distribution system upstream ofconnected load equipment seldom exceeds 2 percent of the loadrequirement.

The loss fraction saved through the installation of capacitors at themotor is: (1-pf original/pffinal)/100

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Power Factor

1) High power losses in the electrical lines

2) High voltage variation in the electrical lines

3) (Oversize of investment) ,oversizing generators, circuit breakers,

electric lines and transformers4) Low performances

Low cos means poor electrical efficiency.

From this, we understand the importance to improve (increase) the

power factor. Capacitors are needed to obtain this result.

Low cos has the following disadvantages:

http://d/My%20Documents/EMPR.ppthttp://d/My%20Documents/EMPR.ppt

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How To Improve Power Factor

The capacitors connected in parallel to the load

generate reverse-phase reactive power.

kW

kVAkvar1

http://d/My%20Documents/EMPR.ppthttp://d/My%20Documents/EMPR.ppthttp://d/My%20Documents/EMPR.ppthttp://d/My%20Documents/EMPR.ppthttp://d/My%20Documents/EMPR.ppthttp://d/My%20Documents/EMPR.ppt

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Capacitors

Capacitors are used to

compensate the Reactive

Power.

The resulting capacitive

current is leading current and

is used to cancel the lagginginductive current flowing from

the supply.