Volumn 4


Shivpal Verma1, Megha Rahangdale2, Mitali Kamdi3, Muskan Pashine4, Shubham Dharapure5, Saurabh Dongre6

Professor1, Student2,3,4,5,6

Department of Electrical Engineering

Dr. Babasaheb Ambedkar College of Engineering and Research, Nagpur

Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur , India


Now-days most of the industries have inductive load so the power demand is increasing day by day. There is use of wide variety of electrical load and power electronic devices which create varying power demand on the supply system so it is very necessary to have automatic switching operation of the capacitor depends upon the load fluctuation. This could be achieved by using Automatic Power Factor Correction Panel (APFC Panels) which consistently maintained the power factor near to the unity i.e. (0.97 to 0.98).this thing will increase the generation and the efficiency of system and the life span of the equipment also increase.

Keywords— Power Factor correction, Reactor, Power factor improvement, APFC Panels, Power Factor, Inductive, Fixed Capacitors.


In modern electrical distribution system most of the loads are inductive in nature. For examples: motors, transformers, coils, generators and induction furnaces. There are two kinds of current are require for inductive loads.

The combination of Real power and Reactive power is called apparent power. The power factor is the ratio of Real power to apparent power.The loads are inductive in nature resulting is several lagging power factor due to this there is loss and wastage of energy which results in high electric bills and heavy penalties from electricity board. So it is very important to maintain the power factor. If load is variable it is very difficult to maintain the Power Factor (near to unity). To overcome this problem APFC panel are introduce which maintain Power Factor.

Day by day cost of electricity is increasing and hence it becomes almost important to cut down on electrical consumption for reducing expenditure. This panel is used in those industries where electrical installation is meant to large electrical load. These APFC panels can effectively and automatically manage quickly changing load with the retention of high Power Factor.

Details of APFC

A. Importance of APFC

As all we know that the most of industrial loads are inductive in nature. So the Power factor is very poor is depends upon the capacity of reactive power. Due to these loads cause the current to lagging the voltages with some angle result in low Power Factor and these low Power Factor. draw heavy internal current which cause excessive heat in the winding of the equipment and huge voltage drop. These low Power Factor required high KVA rating which ultimately increases the cost of the equipment. Also due to the less Power Factor their will be the wastage of energy. As there is wastage of energy the electricity board impose heavy penalty on the consumer. If APFC panel are not used then the Power Factor is reduced to 0.8 to 0.6.

   Figure.1 Electricity Board

To overcome all the drawbacks, the APFC panels are used. APFC panel play an important role to improve the Power Factor (i.e. near to unity) and reduces penalty from the electricity board.

Block Diagram of APFC Panel

As seen above the block diagram of APFC panel. The Supply main terminals are connected to input of APFC Panel. Power factor is sensed by the CT & PT placed in line side. As the level of line voltage and current the capacitor banks are operated to archive calculated power factor by microprocessor based APFC relay. The appropriate capacitor bank will operate with respect to KVAr required to Achieve target PF by APFC panel. After it CT & PT will check the feedback from the switching capacitors. Finally archived or targeted PF given to load.

Automatic power factor correction

A. Displacement power factor correction

An Inductive motor draws current from the supply. This current is made up of resistive components i.e. load current, loss current and inductive components i.e. leakage reactance, magnetizing current.

The leakage reactance current is depends on the total current drawn by the motor, but the magnetizing current is independent of the load on the motor. The magnetizing current is generally between 20% to 60% of the rated full load current of the motor. If the motor is going to operate it is very necessary that the magnetizing current establish the flux in the iron. The magnetizing current done not actually contribute to the actual work output of the motor. The motor should be work property.

For example 100 Amp current of a motor and P.F. is 0.75 and the resistive component of the current is 0.75 and this is what KWH meter measures When current is increases the distribution losses is also increases. The result is (100 * 100) / (75 *75) = 1.777. The P.F. is achieved by the addition of capacitor connected in parallel with motor circuit and can be applied at the starter or switch board or distribution panel. The lagging inductive current flowing from the supply.

B. Displacement Static Correction

As a large proportion of the inductive load on the supply is due to the magnetizing current of induction motors, it is easy to correct each individual motor by connecting the correction capacitors to the motor starters. With static correction, it is important that the capacitive current is less than the inductive magnetizing current of the induction motor. The static power factor correction are employed various installation, the correction capacitors are connected directly in parallel with the motor windings.

When the motor is Off Line, the capacitors are also Off Line. When the motor is connected to the supply, the capacitors are also connected providing correction at all times. This removes the requirement for any expensive power factor monitoring and control equipment.

In this situation, the capacitors remain connected to the motor terminals as the motor slows down. An induction motor, while connected to the supply, is driven by a rotating magnetic field in the stator which induces current into the rotor. When the motor is disconnected from the supply, there is for a period of time, a magnetic field associated with the rotor. As the induction motor decelerates, it generates voltage out its terminals at a frequency which is related to its speed.

The capacitors connected across the motor terminals, form a resonant circuit with the motor inductance. If the motor is critically corrected, (corrected to a power factor of 1.0) the inductive reactance equals the capacitive reactance at the line frequency and therefore the resonant frequency is equal to the line frequency. If the motor is over corrected, the resonant frequency will be below the line frequency. If the frequency of the voltage generated by the decelerating motor passes through the resonant frequency of the corrected motor, there will be high currents and voltages around the motor/capacitor circuit. This can result in severe damage to the capacitors and motor. It is imperative that motors are never over corrected when static correction is employed.

Static power factor correction should provide capacitive current equal to 80% of the magnetizing current, which is essentially the open shaft current of the motor.

The magnetizing current for induction motors can vary appreciably. Typically, magnetizing currents for large two pole machines can be as low as 20% of the rated current of the motor while smaller low speed motors can have a magnetizing current as rise as 60% of the rated full load current of the motor.

Static correction is commonly applied by using one contactor to control both the motor and the capacitors. It is better practice to use two contactors, for motor and capacitors.

C. Working of Capacitor

Induction motors, transformers and many other electrical loads require magnetizing current (kvar) as well as actual power (kW). By representing these components of apparent power (kVA) as the sides of a right triangle, we can determine the apparent power from the right triangle rule: kVA2 = kW2 + kVAR2.

To reduce the kva required for any given load, you must shorten the line that represents the kvar. This is precisely what capacitors do. By supplying kvar right at the load, the capacitors relieve the utility of the burden of carrying the extra kvar. This makes the utility transmission or distribution system more efficient, reducing cost for the utility and their customers.

D. Causes Low Power Factor

 Since power factor is defined as the ratio of KW (Actual Power) to KVA (Apparent Power), we see that low power factor results when KW is small in relation to KVA. Inductive loads. Inductive loads (which are sources of Reactive Power) include:

  1. Transformers
  2. Induction motor
  3. Induction generators (wind mill generators)
  4. High intensity discharge (HID) lighting

These inductive loads constitute a major portion of the power consumed in industrial complex. Reactive power (KVAR) required by inductive loads increases the amount of apparent power (KVA). This increase in reactive and apparent power results in a larger angle   (measured between KW and KVA).  Recall that, as   increases, cosine   (or power factor) decreases.

E. Improvement of Power Factor

The power factor is improved for several different reasons.  Some of the benefits of improving your power factor include:

1. Lower utility fees by:

a. Reducing peak KW billing demand:

Inductive loads, which require reactive power, caused your low power factor. This increase in required reactive power causes an increase in required apparent power, which is what the utility is supplying. So, a facility’s low power factor causes the utility to have to increase its generation and transmission capacity in order to handle this extra demand.

By lowering your power factor, you use less KVAR.  This results in less KW, which equates to a dollar savings from the utility.

b. Eliminating the power factor penalty:

Utilities usually charge customers an additional fee when their power factor is less than 0.95. Thus, you can avoid this additional fee by increasing your power factor.

2. Increased system capacity and reduced system losses in your electrical system

By adding capacitors to the system, the power factor is improved and the KW capacity of the system is increased.

For example, a 1,000 KVA transformer with an 80% power factor provides 800 KW (600 KVAR) of power to the main bus.

By improve the power factor to 90%, more KW can be supplied for the same amount of KVA.

1000 =  (900 KW)2  +  ( ?  KVAR)2

KVAR = 436

 The KW capacity of the system increases to 900 KW and the utility supplies only 436 KVAR.

Uncorrected power factor causes power system losses in your distribution system.  By improving your power factor, these losses can be minimized.  With the current rise in the cost of energy, increased facility efficiency is very desirable.  And with lower system losses, you are also able to add additional load to your system.

3. Increased voltage level in your electrical system and cooler, more efficient motors

The uncorrected power factor causes power system losses in your distribution and transmission system.  As power losses increase, you may experience voltage drops.  Excessive voltage drops can cause overheating and premature failure of motors and other inductive equipment. So, by raising your power factor, you will minimize the voltage drop and avoid related problems.  Your motors will run cooler and be more efficient, with a slight increase in capacity and starting torque.

F. Benefits of power factor correction

  • Reduction in kvar demand.
  • Avoid power factor penalty.
  • Reduction in line loss.
  • Reduction in line current.
  • Reduction in transformer rating.
  • Maintenance free.

G. Benefits of APFC

  • Consistently high power factor under fluctuating load.
  • Prevention of leading power factor.
  • Protect under any internal fault.
  • Under friendly; aesthetically designed enclosure dust


  • Modular design.
  • Well ventilated design.
  • Protection to each step.
  • Good service backup.
  • Door interlock facility.
  • Better reliability and lower losses.
  • Special cables used hence withstands high temp.


  • Steel Rolling mills, Automobile industry, Cement plant, Chemical industry, Sugar Plant, Textile.
  • Hospital, Hotels, malls, Banks.
  • Building  Segment.
  • Railway / Ordinance Work shop


We can conclude that the APFC panels are mainly used for the improvement of power factor. A dip in power factor can attract operational losses and a penalty from electricity board, responsible for electricity supply. APFC panels can effectively and automatically manage quickly changing and scattered loads along with the retention of high power factor.


  1. V.Vaidhyanathan, T.Bhavani Shanker, G.Govinda Rao, H. N.Nagamani, “Performance of insulation systems for low voltage APFC panels during temperature rise test at elevated ambient temperatures,” 2012 IEEE 10th International Conference on the Properties and Applications of Dielectric Materials July 24-28,2012, Bangalore, India
  2. Shubham Tiwari, Bhargavi Rana, Aakash Santoki, Harsh Limbhachiya, Sourav Choubey, “Power Factor Improvement by using APFC Panel,” Department of Electrical Engineering Shroff S R Rotary Institute of Chemical Technology, Vataria, India.
  3. Somnath Saha, Tushar Tyagi, Dhananjay V. Gadre, “ARM® Microcontroller based Automatic Power Factor  Monitoring and Control System,” Netaji Subhas Institute of Technology, New Delhi

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