www.fakengineer.com

contentsIntroductionWhat is power factorImportance of power factorDisadvantages of low power factorCalculation of power factorPower factor correction method Types of power factor correctionPower factor correction unit Conclusion

Introduction

Any industrial process using electric motors (to drive pumps, fans, conveyors, refrigeration plant etc.) introduces inefficiencies into the electricity supply network by drawing additional currents, called "inductive reactive currents".

This can be regulated by regulating an important component of power supply called “power factor”

1) Active power (P), measured in watts (W);

2) Apparent power (S), measured in volt-amperes (VA);

3) Reactive power (Q), measured in reactive volt-amperes (VAr).

AC power flow main three componentsAC power flow main three components::

ACTIVE POWER The actual amount of power being used, or

dissipated, in a circuit is called active power

It is also called as true power

True power is a function of a circuit's dissipative elements, usually resistances (R).

It is measured in watts (symbolized by the capital letter P, as always)

REACTIVE POWER

It is equal to the peak value of that power component that travel back and forth on the line, resulting in zero average ,and thus does no useful work.Reactive loads such as inductors and capacitors dissipate zero powerYet the fact that they drop voltage and draw current gives the deceptive impression that they actually do dissipate power. This “phantom power” is called reactive powerIt is measured in a unit called Volt-Amps-Reactive (VAR)

APPARENT POWER The combination of reactive power and true power is

called apparent power It is the product of a circuit's voltage and current,

without reference to phase angle. Apparent power is measured in the unit of Volt-Amps

(VA) and is symbolized by the capital letter S.

P = True power = VIcosφP = True power = VIcosφ

Q = Reactive power = VIsinφQ = Reactive power = VIsinφ

S = Apparent power = P+jQ = |VI|S = Apparent power = P+jQ = |VI|

What is power factor

It is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1.

Power factor = Active power/Apparent power

Power factor is the percentage of electricity that is being used to do useful work

EXPLANATION In a purely resistive AC circuit, voltage and current

waveforms are in step (or in phase), changing polarity at the same instant in each cycle.

Where reactive loads are present, such as with capacitors or inductors, voltage and current waveforms are not in step (or not in phase), thus result in a time difference between the current and voltage waveforms.

Thus have energy storage in the loads which returns to the source and is not available to do work at the load.

A circuit with a low power factor or with reactive loads will have thus higher currents to transfer at a given quantity of power than a circuit with a high power factor.

Instantaneous and average power calculated from AC voltage and current with a unity power factor (φ=0, cosφ=1)

PURELY RESISTIVE SYSTEM

Instantaneous and average power calculated from AC voltage and current with a zero power factor (φ=90, cosφ=0)

PURELY INDUCTIVE SYSTEM

Instantaneous and average power calculated from AC voltage and current with a lagging power factor (φ=45, cosφ=0.71)

SYSTEM WITH BOTH RESISTIVE AND INDUCTIVE LOAD

Importance of power factor IN INDUSTRIESA power factor of one or "unity power factor" is the

goal of any electric utility company since if the power factor is less than one, they have to supply more current to the user for a given amount of power use.

In so doing, they incur more line losses. They also must have larger capacity equipment in place than would be otherwise necessary.

DISADVANTAGES OF LOW POWER FACTOR

Direct costs of low power factorThis increases generation and transmission costs Loss in distribution capacity Larger InvestmentTransformers Large size conductors

Power factor vs. conductor size

Power factor vs. losses

Power factor correction methodPower factor correction (PFC) is a technique of

counteracting the undesirable effects of electric loads that create a power factor that is less than 1

Power factor correction may be applied either by an electrical power transmission utility to improve the stability and efficiency of the transmission network

Or correction may be installed by individual electrical customers to reduce the costs charged to them by their electricity supplier

Types of power factor correction method

i. Passive PFC

ii. Active PFC

PASSIVE PFCThis is a simple way of correcting the nonlinearity of a load

by using capacitor banks Power factor correction is achieved by the addition of

capacitors in parallel with the connected motor circuits Depending on the load and power factor of the network,

the power factor controller will switch the necessary blocks of capacitors in steps

The resulting capacitive current is leading current and is used to cancel the lagging inductive current flowing from the supply.

It is not as effective as active PFC Switching the capacitors into or out of the circuit causes harmonics

CURRENT VECTORS WITHOUT CORRECTION

LEAKAGELEAKAGE

CURRENTCURRENT

CURRENT VECTORS WITH CORRECTION

TYPES OF PASSIVE PFCSTATIC METHOD

Capacitors connected at each starter and controlled by each starter

BULK METHOD

In this method capacitors are connected at a distribution board and controlled independently from the individual starters

Bulk method

Static method

Active PFC An Active Power Factor Corrector (active PFC) is a power

electronic system that controls the amount of power drawn by a load

In most applications, the active PFC controls the input current of the load by addition of a boost converter that forces a sinusoidal input so that the current waveform is proportional to the mains voltage waveform (a sinewave).

This requires additional semiconductor switches and control electronics, but permits cheaper and smaller passive components

Active PFC is the most effective and can produce a PFC of 0.99 (99%).

That feature is particularly welcome in power supplies for laptops and cell phones.

Power factor correction unitAn automatic power factor correction unit is equipment

used to improve power factor, in industrial networks. By increasing the power factor to near 1, current is

reduced in the power system and usually utility charges for electrical power are reduced.

It usually consists of a number of capacitors that are switched by means of contactors.

BENEFITS OF POWER FACTOR CORRECTION

Reduce Utility Power Bills.Reduction in load current.Increase in voltage level across the load.Improve System Operating Characteristics. (Reduce

Line Losses)Reduces the size of conductor required.

CONCLUSION Improvement of power factor is necessary in both

consumer and supplier point of view. In some industries penalty is charged due to maintenance of low power factor. In some industries where power consumed by the load is low, high ratings of equipments are required. SVC Technologies and Synchronous Generator are used for the improvement of power factor.