This document discusses automatic power factor correction units. It begins by explaining what power factor is and how inductive loads can cause low power factors. It then describes why power factors should be improved, such as reducing energy losses. The document outlines different methods to correct power factor, and why automatic correction is needed since loads and power factors vary. It provides details on how an automatic power factor correction unit works, including using sensors to measure voltage, current and power factor, and switching capacitors in or out to maintain a high power factor. In conclusion, automatic power factor correction can improve efficiency and minimize line losses for industrial and commercial facilities.

1. AUTOMATIC POWER FACTOR
CORRECTION UNIT
Presented by:
Febin Paul

2. CONTENT
INTRODUCTION
POWER FACTOR
WHAT CAUSES LOW PF?
WHY SHOULD WE IMPROVE PF?
METHODS TO CORRECT POWER FACTOR
NEED FOR AUTOMATIC POWER FACTOR
CORRECTION
BENEFITS OF APFC
AUTOMATIC POWER FACTOR CORRECTION UNIT
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3. INTRODUCTION
In our country, energy crisis is one of the major concerns.
Effective power transmission and power utilization of this
power is one of the main issues.
The Power Factor is the invisible factor, which causes a
great loss of electrical energy and also damages electrical
equipment.
The Power Factor of varying load can be measured and
compensated using static method.
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4. POWER FACTOR
It is defined as the cosine of the angle between the
voltage and current phases. It may also be defined as the ratio
of kW and the kVA drawn by the electrical load where kW is
the actual load power and kVA is the apparent power.
Active (or Working) Power is to perform the useful work. --
kW
Reactive Power is to create and maintain electro-magnetic
fields produced by magnetic Equipment. -- kVAR
Apparent (or Total) Power is the vector sum of the active
power and reactive power. -- kVA
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5. WHAT CAUSES LOW POWER
FACTOR?
Most of the motors used in industries are of induction type,
which have low lagging pf.
High intensity discharge lamps operate at low lagging pf.
Transformers system work at lagging pf.
Load on the system is varying which results in decreasing or
low pf.
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Ø
KW
KVAR
KW
KVARKVAR
Ø
Figure: Power Triangle

6. 19 March 2017 6
WHY SHOULD WE IMPROVE
P.F?
Reduction in
Transformer Rating
Reduction in kVAR
Demand
Advantages of P.F
Correction
Reduction in kVA
Demand
Reduction in Line
Current
Reduction in Line
loss
Reduction in
Cable / Bus-bar
size
Reduction in
Switchgear
Rating
Avoid power factor
penalties
Reduction in kVA
Demand
Reduction in
Transformer Rating
Avoid power factor
penalties
Reduction in
Transformer Rating
Avoid power factor
penalties
Reduction in
Transformer Rating
Avoid power factor
penalties
Advantages of PF
Correction
Reduction in
Switchgear
Rating
Figure: Advantages of PF Correction

7. NEED FOR APFC
Power factor also varies as a function of the load
requirements.
Difficult to maintain a consistent power factor due to the use
of fixed Compensation i.e. fixed capacitors.
Automatic variation is the compensation to suit the load
requirements.
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8. BENEFITS OF APFC
Consistently high power factor under fluctuating loads
Eliminate power factor penalty
Lower energy consumption by reducing losses.
Continuously sensing and monitoring the load
Automatically switch on/off relevant capacitors steps for
consistent power factor.
Ensures easy user interface
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9. AUTOMATIC POWER FACTOR
CORRECTION UNIT
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Figure: System Block Diagram

10. AUTOMATIC POWER FACTOR
CORRECTION UNIT(CONTD…)
It includes:
Power Factor Measurement
AC Current Measurement
AC Voltage Measurement
Capacitor can be added/removed in case of lagging/leading
power factor..
The capacitor will be added in parallel to the load.
Voltage & current is needed to measure required for reactive
power, apparent and active power.
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11. POWER FACTOR
MEASUREMENT
A zero crossing detector can be used for calculating phase of
voltage and Current.
 The input of this circuit is a sine wave and output is a square
wave.
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Figure: Zero Crossing Detector

12. POWER FACTOR MEASUREMENT
(CONTD…)
Opto-Coupler Circuit is used to trimmed out the negative
portion of the output from Zero Crossing Detector.
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Figure: Opto-Coupler Circuit

13. POWER FACTOR
MEASUREMENT(CONTD…)
The output from Opto-Coupler fed into EXOR gate that
gives the resultant phase difference between voltage and
current.
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Figure: EXOR Working

14. POWER FACTOR
MEASUREMENT (CONTD…)
The on-time of above waveform is measured by using
interrupt routine in microcontroller.
Once the time is measured the phase difference can be
measured by following formula.
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15. AC VOLTAGE MEASUREMENT
AC voltage converted to pulsating DC voltage by using
super diode.
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Figure: Super Diode

16. AC VOLTAGE
MEASUREMENT(CONTD…)
To bring voltage in safe operating region a center tapped step
down voltage transformer is used and half bridge full wave
rectifier
SD4 and SD5 represents super diode circuit.
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Figure: Circuit for Measuring AC Voltage

17. AC VOLTAGE
MEASUREMENT(CONTD…)
The pulsating DC is fed into the controller and 2000 samples
were taken. All the samples were added and divided by
2000 to get average input voltage.
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18. AC CURRENT MEASUREMENT
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Figure: Circuit for Measuring AC Current

19. AC CURRENT
MEASUREMENT(CONTD…)
The AC current can be measured by microcontroller by
converting in to a voltage within the controller
readable range. A current transformer is
used for converting high load current in a safe
operating range. Current is converted in
voltage by connecting two power
resistors in series and center tapping
them.
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20. EXPERIMENTAL SETUP
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Figure: System Schematic diagram

21. POWER FACTOR
CORRECTION
Based on the measured values (phase shift, voltage &
current), all three powers and power factor of load is
calculated.
Based on these values the required capacitance is determined
and switched in or out by solid state relays.
A relay is placed in series before
bank and load as a protection for themselves.
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22. APFC SYSTEM
19 March 2017 22Figure: APFC SYSTEM

23. CONCLUSION
This technique used to overcome power losses due to low
power factor associated with common household and small
industrial units.
By installing suitably sized capacitors into the circuit the
Power Factor is improved and the value becomes nearer to
unity thus minimising line losses and improving the
efficiency of a plant.
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24. REFERENCE
1) Muhammad Bilal Khan, Muhammad Owais, “Automatic Power Factor
Correction Unit”, 2016 International Conference on Computing,
Electronic and Electrical Engineering (ICE Cube), Date of
Conference: 11-12 April 2016
2) Dr. Satadal Mal, Reetam Sen Biswas, “Automatic Power Factor
improvement using Microcontroller”, 2015 International Conference
and Workshop on Computing and Communication (IEMCON), Date of
Conference: 15-17 Oct. 2015
3) Chun-Lien Su, Ming-Chao Lin, Chi-Hsiang Liao, “A Energy-Savings
Evaluation Method to Justify Automatic Power Factor Compensators
on Marine Vessels”, Industry Applications Society Annual Meeting
(IAS), 2012 IEEE, Date of Conference: 7-11 Oct. 2012
4) Aparna Sarkar ,Umesh Hiwase , “Automatic Power Factor Correction
by Continuous Monitoring”, International Journal of Engineering and
Innovative Technology (IJEIT) Volume 4, Issue 10, April 2015
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