World University of Bangladesh

Welcome to our presentationPresentation Topic:Power Factor Improvement.Presented to: Presented by:Md. Aminul Islam Md. Shahin Shake Md. Tayeb Md. Sohel Rana Md. Rezaul Sujan Chandra Das

Power Factor

• The term power factor comes into picture in AC circuits only. “The cosine of angle between voltage and current in an a.c.  circuit is known as power factor”.• It refers to the fraction of total power (apparent power) which

is utilized to do the useful work called active power. Thus, Power Factor

Need for Power Factor Improvement

• Environmental benefit. Reduction of power consumption due to improved energy efficiency. Reduced power consumption means less greenhouse gas emissions and fossil fuel depletion by power stations.

• Reduction of electricity bills• Extra kVA available from the existing supply• Reduction of I2R losses in transformers and distribution

equipment.• Reduction of voltage drop in long cables.• Extended equipment life – Reduced electrical burden on cables and electrical components.

Disadvantages of Low Power Factor

In case of Low Power Factor, Current will be increased, and this high current will cause to the following disadvantages.

1. Large Line Losses (Copper Losses): We know that Line Losses is directly proportional to the squire of current I2. Power Loss = I2xR i.e., the larger the current, the greater the line

losses.3. Greater Conductor Size and Cost: In case of low power factor, current will be increased, thus, to

transmit this high current, we need the larger size of conductor. Also, the cost of large size of conductor will be increased.

Disadvantages of Low Power Factor

4. Large Voltage Drop: Voltage Drop , V = IZ. Now in case of Low Power factor, Current will be increased. So the Larger the current, the Larger the Voltage Drop.5. Poor Voltage Regulation Voltage Regulation = V.R = (VNo Load – VFull Load)/ VFull Load

In case of Low Power Factor there would be large voltage drop which cause low voltage regulation. Therefore, keeping Voltage drop in the particular limit, we need to install Voltage regulators.

Causes of Low Power Factor

The following are the causes of low power factor:• Most of the a.c. motors are of induction type which have low

lagging power factor. These motors work at a power factor which is extremely small on light load (0·2 to 0·3) and rises to 0·8 or 0·9 

at full load.• Arc lamps, electric discharge lamps and industrial heating furnaces  operate at low lagging power factor.

How to improve power factor

The low power factor is mainly due to the fact that most of the power loads are inductive and, therefore, take lagging currents.In order to improve the power factor, some device taking 

leading power should be connected in parallel with the load.

Methods for Power Factor Improvement

The following devices and equipments are used for Power Factor Improvement.

• Static Capacitor• Synchronous Condenser• Phase Advancer

Static Capacitor

• The power factor can be improved by connecting static capacitors  in parallel with the equipment operating at lagging power factor.

Static Capacitor To illustrate the power factor improvement by a capacitor, considera single phase load taking lagging current I at a power factor cos ϕ1 as shown in Fig. 6.3.The capacitor C is connected in parallel with the load. The capacitor draws current  IC which leads the supply voltage by 90◦.The resultingline current I′ is the phasor sum of I and IC and its angle of  lag is ϕ2 as shown in the phasor diagram of Fig. 6.3. (iii). It is clear that ϕ2  is less than ϕ 1 , so that cos ϕ2 is greater than cos ϕ1. Hence, the power factor of the load is improved. 

Static Capacitor The following points are worth noting:i. The circuit current I′ after p.f. correction is less than the original  circuit current I.ii. The active component remains the same before and after p.f. correction 

because only the lagging reactive component is reduced by the capacitor. ∴ I cos ϕ1 = I′ cos ϕ2iii. The lagging reactive component is reduced after p.f. improvement and 

is equal to the difference between lagging reactive component of load  (I sin ϕ1) and capacitor current (IC) i.e., I′ sin ϕ2 = I sin ϕ1 – IC

Static Capacitor

iv.  As I cos ϕ1 = I′ cos ϕ2 ∴ VI cos ϕ1 = VI′ cos ϕ2 Therefore, active power (kW) remains unchanged due to power factor  improvement.v. I′ sin ϕ2 = I sin ϕ1 – IC

∴ VI′ sin ϕ2 = VI sin ϕ1 – VIC

i.e. Net kVAR after p.f. correction  = Lagging kVAR before p.f. correction − leading kVAR of equipment.

Advantages & Disadvantages of Static Capacitor

Advantages• They have low losses.• They require little maintenance as there are no rotating parts.• They can be easily installed as they are light and require no foundation

. Disadvantages• They have short service life ranging from 8 to 10 years.• They are easily damaged if the voltage exceeds the rated value.• Once the capacitors are damaged, their repair is uneconomical.

Synchronous Condenser• When a Synchronous motor operates at No-Load and over-exited

then it’s called a synchronous Condenser. • Whenever a Synchronous motor is over-exited then it provides

leading current and works like a capacitor. When a synchronous condenser is connected across supply voltage (in parallel) then it draws leading current and partially eliminates the re-active component and this way, power factor is improved. Generally, synchronous condenser is used to improve the power factor in large industries.

Synchronous Condenser

Synchronous Condenser Fig 6.5 shows the power factor improvement by synchronous  condenser method. The 3-ϕ load takes current IL at low lagging  power factor cos ϕL. The synchronous condenser takes a current Im  which leads the voltage by an angle ϕm.  The resultant current I is the phasor sum of Im and IL and lags

behind the voltage by an angle ϕ.  It is clear that ϕ  is less than ϕL so that cos ϕ is greater than cos ϕL. Thus the power factor is increased from cos ϕL to cos ϕ. 

Advantages & Disadvantages of Synchro. Condenser

Advantages• By varying the field excitation, the magnitude of current drawn by the

motor can be changed by any amount. This helps in achieving  stepless control of power factor.• The motor windings have high thermal stability to short circuit  currents.• The faults can be removed easily. Disadvantages• There are considerable losses in the motor.• The maintenance cost is high.• It produces noise

Phase Advancer

Phase advancer is a simple AC exciter which is connected on the main shaft of the motor and operates with the motor’s rotor circuit for power factor improvement. As the stator windings of induction motor takes lagging current 90° out of phase with Voltage, therefore the power factor of induction motor is low. If the exciting ampere-turns are excited by external AC source, then there would be no effect of exciting current on stator windings. Therefore the power factor of induction motor will be improved.

Phase advancer is used to improve the power factor of induction motor in industries.

Advantages of Power factor improvement

Following are the merits and benefits of improved Power factor:

• Increase in efficiency of system and devices• Low Voltage Drop• Reduction in size of a conductor and cable which reduces cost

of the Cooper• An Increase in available power• Line Losses (Copper Losses) I2R is reduced.

Advantages of Power factor improvement

• Appropriate Size of Electrical Machines (Transformer, Generators etc).

• Low kWh (Kilo Watt per hour).• Saving in the power bill.• Better usage of power system, lines and generators etc.• Saving in energy as well as rating and the cost of the electrical

devices and equipment is reduced.

Thank You for Your Attention