Fayoum University
Faculty of Engineering
Electrical Power and machine department
Power Factor Correction
Submitted By :
Mahmoud Ahmed
Sayed Ahmed
Submitted to
Dr.Eng / Ahmed Fouad
Contents
Power Factor Correction ....................................................................................... i
1.
Introduction: .................................................................................................... 1
2.
Power Factor : ................................................................................................. 1
2.1 Causes of low power factor .................................................................... 3
2.2 Disadvantages of low power factor: ...................................................... 3
3.
Power factor correction: ................................................................................. 4
3.1 Advantages of power factor correction: ............................................... 5
3.2 Methods Of Power Factor Correction Or Improvement .................... 6
3.2.1 Capacitor Bank ......................................................................... 7
A.
Advantages ................................................................................ 8
B.
DisAdvantages ........................................................................... 8
3.2.2 Synchronous Condenser ........................................................... 9
A.
Advantages .............................................................................. 10
B.
DisAdvantages ......................................................................... 10
3.2.3 Phase Advancer ....................................................................... 11
A.
Advantages .............................................................................. 12
B.
DisAdvantages ......................................................................... 12
Power Factor Correction
1. Introduction:
- To obtain the best economic advantage from your electricity supply, both the
generating plant and your own plant should be operated at high efficiency.
- To maintain this level of efficiency, a high power factor throughout the system is
essential.
- Power Factor is a measure of how efficiently electrical power is consumed
- Power factor correction (PFC) is the process of adjusting the characteristics of
electric loads that create a power factor that is less than 1.
2. Power Factor :
- Consider a single-phase induction motor
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Power Factor Correction
-
An inductive load requires a magnetic field to operate and in creating such a magnetic
field causes the current to be out of phase with the voltage (the current lags the voltage).
 Active Power (P) = the power needed for useful work such as turning a lathe,
providing light or pumping water, expressed in Watt or KiloWatt (kW)
 Reactive Power (Q) = a measure of the stored energy reflected to the source which
does not do any useful work, expressed in var or Kilovar (kVAR)
 Apparent Power (S) = the vector sum of active and reactive power, expressed in
Volt Amperes or in KiloVolt Amperes (kVA)
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Power Factor Correction
- The power factor can be expressed in two ways:
a. Power factor (pf) = Useful power (kW) divided by the total power (kVA)
P.F = P/S
b.
Power factor (pf) = The cosine of the angle between useful power and total
power = cos ø.
- Power Factor measures how effectively electrical power is being used It is a
sinusoidal waveform and therefore expressed as dimensionless number between -1
and 1,
2.1
Causes of low power factor:
1. Variations In Power System Loading.
2. Significant phase difference between the voltage and current at the load terminals
3. light loading conditions for Induction motors.
4. High harmonic content or distorted/discontinuous current waveform.
2.2
Disadvantages of low power factor:
1. Increases electricity costs
2. Cause overloading of generators, transformers, and distribution system
3. Greater voltage drops and power losses
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Power Factor Correction
4. Low efficiency and unnecessary wear and tears of industrial electrical equipment.
3. Power factor correction:
-
A low power factor is mainly due to lagging currents drawn by inductive loads, Most loads on
an electrical distribution system can be categorised into three main types:
a) Resistive
b) Inductive
c) Capacitive
- The most common type of load is inductive. For example, fluorescent lights,
transformers and AC induction motors. note the following points:
a) For pure inductance, current lags behind voltage by 90°.
b) For pure capacitance, current leads voltage by 90°.
So,
the solution is simple. If we use capacitors to draw leading current, we can cancel
the effects of lagging inductive current and hence improve the power factor.
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Power Factor Correction
- The above fig shows a common circuit. The R and L are present in all inductive
equipments and the C is used for pf improvement.
Here, IL = current drawn by the circuit capacitor C isn't used,
ϕL = phase angle between voltage V and load current IL,
IC = capacitive current drawn by C,
I = resultant current when C is used,
ϕ = phase angle between voltage V and net current I.
- As shown in the above phasor diagram, ϕ < ϕL
- Therefore cos ϕ > cos ϕL, hence power factor is improved
Based upon this principle, many methods are used for power factor correction
(PFC).
3.1 Advantages of power factor correction:
1. Avoid power factor penalties
2. Improve plant efficiency
3. Improved network Voltage.
4. Additional loads can be added to the system
5. Reduce overloading of cables, transformer, switchgears, etc..
6. Reduce demand charging.
7. Increased load capabilities of the load in existing circuits.
8. Reduced power system losses.
9. Improved starting torque for motors
5
Power Factor Correction
3.2 Methods Of Power Factor Correction Or Improvement
1) Capacitor Bank
2) Synchronous Condenser
3) Phase Advancer
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Power Factor Correction
3.2.1 Capacitor Bank
- Simplest method.
- applied at areas where large inductive loads (lagging currents) are present.
- Static capacitors are used which produce capacitive reactance that cancels out the
inductive reactance of the lagging current.
- These banks can be star connected or delta connected.
- A control system is usually provided which monitors the pf and switches the
capacitors ON or OFF.
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Power Factor Correction
A. Advantages

low losses

low maintenance

light weight

easy to install

no foundation required
B. Disadvantages

short life (8-10 years)

capacitors can get easily damaged due to over voltage

once damaged, the repair is costly and uneconomic

due to constant switching, switching surges and harmonics may be produced
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Power Factor Correction
3.2.2 Synchronous Condenser
- When a synchronous motor is over excited, it draws leading current. In a way, it
behaves like a capacitor.
- When such a motor is over excited and run at no load, it is called a Synchronous
Condenser.
- The most attractive feature is that it allows stepless pf correction. In a static
capacitor, the leading kVAR supplied are constant. But in a synchronous
condenser, we can vary the field excitation and hence control the amount of
capacitive reactance produced.
- Synchronous Condensers are used in large factories, industries and major supply
substations.
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Power Factor Correction
A. Advantages

longer lifespan (almost 25 years)

flexible and stepless control of pf

reliable

does not get affected by harmonics

No switching is required hence harmonics are not produced
B. Disadvantages

higher losses

expensive

higher maintenance costs

produces noise

Synchronous motor is not self starting, so auxiliary device is needed.

uneconomical for equipment below 500 kVA
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Power Factor Correction
3.2.3 Phase Advancer
- Can be used only for Induction Motors
- We know that stator winding draws lagging current in a motor. This current is
drawn from the main supply.
- Hence, to improve pf, we supply this lagging current from an alternative source.
This alternative source is the phase advancer.
- A phase advancer is basically an AC exciter. It is mounted on the same shaft as
the main motor and connected in the rotor circuit. It supplies exciting ampere
turns to the rotor circuit at slip frequency. This improves the power factor.
- Another attractive feature is that if we supply more amp-turns than needed, the
motor will operate in an over excited state (at leading pf).
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Power Factor Correction
A. Advantages

Lagging kVAR drawn by the motor are reduced because the exciting ampere
turns are supplied at slip frequency.

Can be utilized easily where synchronous motor is inadmissible
B. Disadvantages

Uneconomical for motors below 200 HP (150 kW)
-
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