power factor 3.doc

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Power Factor Improvement


A report submitted in Technical paper

presentationBachelor of Technology

In

Electrical & Electronics Engineering

By

S.NAGENDRA KUMAR (08NF1A0254)

S.KRISHNARJUNA RAO (08NF1A0255)

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

UNIVERSAL COLLEGE OF ENGINEERING AND TECHNOLOGY

(Affiliated to JNTU Kakinada)

Dokiparru (V), Medikonduru (M), Guntur - 522438.

ABSTRACT

UCET-B.TECH Dept of EEE


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Today, there is a rapid usage of electrical power in every sector. To meet the increasing

load demand, we must increase the power development which results an increase in reactive

power. With the increase of reactive power, the power factor will reduces. Low power factor

causes the ratings of generators and transformers, cross-sectional area of the bus-bars and the

contact surface of the switchgear, the size of the feeders and distributors, energy losses;

voltage drops in generators, transmission lines and distributors to increase. In this paper, we

are going to see the types of power, disadvantages of low power factor, Methods to improve

the power factor to unity and the advantages of improving the power factor.



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The significance of power factor lies in the fact that utility companies supply customers

with volt-amperes, but bill them for watts. Power factors below 1.0 require a utility to

generate more than the minimum volt-amperes necessary to supply the real 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 be 1.4 times the current required at 1.0 power factor, so the

losses in the circuit would be doubled (since they are proportional to the square of the

current). Alternatively all components of the system such as generators, conductors,

transformers, and switchgear would be increased in size (and cost) to carry the extra current.

Utilities typically charge additional costs to customers who have a power factor below some

limit, which is typically 0.9 to 0.95. Engineers are often interested in the power factor of a

load as one of the factors that affect the efficiency of power transmission.

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2 WHAT IS POWER FACTOR?

Power Factor is a term used to describe the efficiency of your electrical power supply.

The Power Factor of an AC electric power system is defined as the ratio of the "Real Power"

to the "Apparent Power", and is expressed as a number between 0 and 1 (as a percentage, ex.

0.5 equals 50% power factor).

Power Factor consists of 3 components:UCET-B.TECH Dept of EEE


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KW (Kilowatts)- the working, or Real Power;

KVA - (Kilovolt Amps) the Apparent Power, and;

KVAR- (Kilovolt Amps Reactive) the Reactive Power.

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Due to energy stored in the load and returned to the source, or due to a non-linear load

that distorts the wave shape of the current drawn from the source, the Apparent Power can be

greater than the Real Power. This process causes low-power-factor loads, which then

increase losses in a power distribution system and result in increased energy costs.

Consequently, as the KVA use decreases, the Power Factor of the load increases, based on a

constant KW. To determine your Power Factor, divide the working power (KW) by the

Apparent Power (KVA). The Power Factor, as stated can then be expressed as a percent of 1,



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with 1 or unity being the highest (or best) factor possible. When correcting Power Factor in

general, a measurement of .9 or higher is considered good.

How Reactive Power Is Generated:

Every electric load that works with magnetic fields (motors, chokes, transformers,

inductive heating, arc-welding generators) produces a varying degree of electrical lag, what is

called inductance. This lag of inductive loads maintains the current sense (e.g. positive) for a

time even though the negative going voltage tries to reverse it. This phase shift between

current and voltage is maintained, current and voltage having opposite signs. During this

time, negative power or energy is produced and fed back into the network. When current andvoltage have the same sign again, the same amount of energy is again needed to build up the

magnetic fields in inductive loads. This magnetic reversal energy is called reactive power. In

alternating voltage networks (50/60 Hz) such a process repeats 50 or 60 times a second. So an

obvious solution is to briefly store the magnetic reversal energy in capacitors and relieve the

network (supply line) of this reactive energy. For this reason, automatic reactive power

compensation systems (detuned/conventional) are installed for larger loads like factory

plants. Such systems consist of a group of capacitor units that can be cut in and cut out and

which are driven and switched by a power factor controller as determined by a current

transformer.

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4

3 POWER FACTOR MANAGEMENT AND IMPROVEMENT

Power Factor improvement is one of the fastest ways to achieving Energy

Conservation and improving the bottom line. Following is required to be done for

Improvement of power factor.

Study of various types of loads.

Determination of the percentage of Inductive load.

Determination of Transformer Capacity

Determination of Power Factor under full load conditions by calculating the

impedance of the transformer.

Once the data is made available the KVA required to improve the power factor to the

levels desired is determined. The next step would be to determine the banking pattern in

the electrical system. This is done by first classifying the loads as major or minor.

Second, to install capacitors at all major loads and finally to install capacitors at the PCC

levels for the fine tuning of power factor preferably with the minimum banking pattern.

The effects of current, voltage, harmonics and temperature are to be addressed. Theseproduce degradations in capacitors and contactors. These go unnoticed since the

equipment is operating silently in a corner, until a catastrophic breakdown occurs.



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4 DISADVANTAGES OF LOW POWERFACTOR

The current for a given load supplied at constant voltage will be higher at a lower power

factor and lower at higher power factor. The higher current due to poor power factor affectsthe system results in following advantages.

i. Rating of generators and transformers are proportional to their output current

hence inversely proportional to power factor, therefore , large generators and

transformers are required to deliver same load but a lower power factor

ii. The cross-sectional area of the bus-bar and the constant surface of the switch gear

is required to be enlarged for the same power to be delivered but a lower power

factor.iii. For the same power to be transmitted but a lower power factor, the transmission

line or distributor or cable have to carry more current. The size of the conductor

will have to be increased if current density in the line is to be kept constant. Thus

more conductor material is required for transmission lines, distributors and cables

to deliver the same load but at lower power factor.

iv. Energy loses are proportional to the square of the current hence inversely

proportional to the square of the lower power factor i.e. more energy losses incur

at low power factor, which results in poor efficiency.

v. Low lagging power factor results in large voltage drop in generators, transformers,

transmission lines and distributors which results in poor regulation.

vi. Low lagging power factor reduces the handling capacity of all the elements of the

system.

Thus we see that the low power factor leads to a high capital cost for the alternators,

switch gears, transformers, transmission lines, distributors, and cables etc.

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5 METHODS OF POWERFACTOR IMPROVEMENT

The low power factor is almost invariably due to inductive nature of load current.

Let the current drawn by an inductive circuit be I lagging behind the applied voltage byan angle . The leading current required to neutralize the lagging reactive component of

current drawn by the inductive (equipment) to give unity power factor.

I sin = I [1-(pf)2]

Power factor can be improved by the following methods:

i. By the use of Static Capacitor.

ii. By the use of Synchronous Machines.

a. By the use of Synchronous Motorsb. By the use of Synchronous Condensers

iii. By the use of Phase Advancers.

iv. By the use of Synchronous-Induction Motors.

v. By the use of High Power factor Motor

By use of static capacitor:

Power factor can be improved by connecting the capacitors in parallel with the

equipment operating at lagging power factors such as induction motors, fluorescent tubes.

Advantages:

Small losses (less than 0.5 percent)

Higher efficiency (up to 99.6%)

Low initial cost

Easy installation being lighter in weight Capability to operate under ordinary atmospheric conditions

Drawbacks:

short service life (8 to 10 years)

gets damaged on over-voltage conditions

uneconomical repair

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CALCULATIONS AND TABLES

Calculation and selection of required capacitor rating

Qc = P * {tan [acos (pf1)] - tan [ acos (pf2)]}

Qc = required capacitor output (kVAr)

pf1 = actual power factor

pf2 = target power factor

P = real power (kW)

The required capacitor output may be calculated as follows:

select the factor (matching point of actual and target power factor) k

calculate the required capacitor rating with the formula:

Qc = k * P

Example:

actual power factor = 0.70, target power factor = 0.96, real power = P = 500kW,

Qc = k * P = 0.73 * 500kW = 365 kVAR

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The table below shows the values for typical power factors in accordance with the above

formula



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0.7 0.75 0.8 0.85 0.9 0.92 0.94 0.96 0.98 1

Actual

Power

Factor

0,40 1.27 1.41 1.54 1.67 1.81 1.87 1.93 2 2.09 2.29

0,45 0.96 1.1 1.23 1.36 1.5 1.56 1.62 1.69 1.78 1.98

0.5 0.71 0.85 0.98 1.11 1.25 1.31 1.37 1.44 1.53 1.73

0,55 0.5 0.64 0.77 0.9 1.03 1.09 1.16 1.23 1.32 1.52

0,60 0.31 0.45 0.58 0.71 0.85 0.91 0.97 1.04 1.13 1.33

0,65 0.15 0.29 0.42 0.55 0.68 0.74 0.81 0.88 0.97 1.17

0,70 0 0.14 0.27 0.4 0.54 0.59 0.66 0.73 0.82 1.02

0.75 0 0.13 0.26 0.4 0.46 0.52 0.59 0.68 0.88

0,80 0 0.13 0.27 0.32 0.39 0.46 0.55 0.75

0.85 0 0.14 0.19 0.26 0.33 0.42 0.62

0,90 0 0.06 0.12 0.19 0.28 0.48

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By use of Synchronous Machines:

i. By use of Synchronous Motors:

Synchronous motors are designed for 1.0-0.8 leading power factors at full load.

The unity power factor motor costs less and has a higher efficiency, but if fully

loaded, it cannot furnish leading reactive KVA to compensate for lagging reactive

KVA in the system.

ii. By use of Synchronous condensers:

An over-excited synchronous motor running on no-load is called the

Synchronous condenser and behaves like a capacitor, the capacitive reactance of

which depends on the motor excitation. Power factor can be improved by using

synchronous condensers like shunt capacitors connected across the supply.

The advantages of synchronous condensers over static capacitors as a power factor

correction devices are:

A finer control can be obtained by variation of field excitation

Inherent characteristic of synchronous condensers of stabilizing variations in

the line voltage and there by automatically aid in regulation. Possibility of over loading a synchronous condenser for short periods, and

Improvement in the system stability

The disadvantages of synchronous condensers over static capacitors are:

Except in size of above 5000KVAR, the cost is higher than that of static

capacitors of the same rating

Comparatively higher maintenance and operating costs

Comparatively lower efficiency due to losses in rotating parts

Noise is produced in operation

An auxiliary equipment is required for starting synchronous condensers

Possibility of synchronous condensers falling out of synchronism causing in

interruption of supply, and

Increase of short-circuit currents when the fault occurs near the synchronous

condensers.



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By use of phase advancers:Shunt and series type of phase advancers are available according to whether the exciting

winding of the advancer is connected in series or parallel with the rotor winding of the

induction motor.

Advantages:

Lagging KVAR dawn by the motor are considerably reduced due to supply of

exciting ampere-turns at slip frequency and The phase advancers can be conveniently employed where the use of synchronous

motor is inadmissible.

By use of Synchronous-Induction Motors:

These are special type of motors which operates at certain loads as synchronous motors

and at other loads as induction motors.

By use of High Power Factor Motors: Besides synchronous induction motors there are other several types of motors which

operate at a power factor of nearly unity as compensated induction motors, and Schrage

motors. These motors are more expensive and have higher maintenance cost than ordinary

induction motors.



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6 BENEFITS OF POWER FACTOR IMPROVEMENT

Power factor correction reduces the reactive power in a system. Power

consumption and thus power costs drop in proportion.

Effective installation use An improved power factor means that an electricalInstallation works more economically (higher effective power for the same

apparent power).

Improved voltage quality

Fewer voltage drops

Optimum cable dimensioning Cable cross-section can be reduced with

improvement of power factor (less current). In existing installations for instance,

extra or higher power can be transmitted.

Smaller transmission losses the transmission and switching devices carry less

current, i.e. only the effective power, meaning that the ohmic losses in the leads

are reduced.

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7 CONCLUSION

The Intelligent Power Factor Controller improves energy efficiency by benefiting

optimum utilization of demand, Reduce line losses, Extra load can be connected without anyadditional demand sanction, Demand penalty can be avoided, Efficiency of plant increases,

zero cost maintenance, increases capacitors life, Helps to avoid increase in system voltage .

By energy conservation, the user is able to achieve a significant competitive edge in the

global context as well as address a normal polarity.

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8 REFERENCES

http://en.wikipedia.org/wiki/Power_factor

J.B.GUPTA.,A COURSE IN POWER SYSTEMS, KATSON BOOKS.

http://www.conzerv.com/PDF/Articles/POWER%20FACTOR%20IMPROVEMENT.pdf

WWW.POWERQUALITY.COM

http://www.squared.com/us/services_support/squared_services.nsf/LookupFiles/PF_F

undametals.pdf/$file/PF_Fundametals.pdf

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