# “Power Factor” In Transmission System

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“Power Factor” In Transmission System

contents Introduction What is power factor Importance of power factor
Disadvantages of low power factor Calculation of power factor Power factor correction method Types of power factor correction Power 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”

AC power flow main three components:
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).

ACTIVE POWER It is also called as true 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 power Yet 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 power It 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 = VIcosφ Q = Reactive power = VIsinφ 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.

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

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

SYSTEM WITH BOTH RESISTIVE AND INDUCTIVE LOAD
Instantaneous and average power calculated from AC voltage and current with a lagging power factor (φ=45, cosφ=0.71)

Importance of power factor IN INDUSTRIES
A 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.

Direct costs of low power factor This increases generation and transmission costs Loss in distribution capacity Larger Investment Transformers Large size conductors

Power factor vs. conductor size

Power factor vs. losses

Power factor correction method
Power 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
Passive PFC Active PFC

PASSIVE PFC This 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
LEAKAGE CURRENT CURRENT VECTORS WITHOUT CORRECTION

CURRENT VECTORS WITH CORRECTION

TYPES OF PASSIVE PFC STATIC 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 unit
An 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.

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