What is Power Factor? How to calculate Power Factor?
Power Factor how to calculate? |Power Factor (PF) is the ratio of working power or the true power of a circuit measured in kilowatts (kW) to apparent power or the total power running through the circuit measured in kilovolt Amperes (kVA).
TRUE POWER (TP)
The actual amount of power dissipated by a circuit. This is measured in kiloWatts (kW).
Measuring True Power in a DC circuit
In DC circuits and purely resistive circuits, the total power supplied by the source is consumed by the resistance. Therefore, no energy losses happen due to the reactance and the Power Factor becomes 1.
Measuring True Power in an AC circuit.
REACTIVE POWER (RP)
During the operation, inductive and capacitive loads continuously drop voltages and draw current from the power source in its first cycle and return some part of it to the source in its next cycle. However, these voltage drops and current draws are in the form of heat or waste energy and they do not do any actual work. But it’s the phantom power which helps transformers to transform power, generators to generate power and motors to rotate. This form of power dissipation is measured in Volt Amperes Reactive (VAR) and called as Reactive Power.
Inductive and capacitive circuits also have voltage and current but no actual power consumption. Therefore, the expression of P=VI is no longer valid when calculating the True Power and it does not give the actual power consumed by the circuit. In the inductive and capacitive circuit voltage and current are not in phase and they are always out of phase with a phase difference between 0-90. Hence, to determine the real power of these circuits the phase difference between the voltage and current waveforms also should be taken into the equation.
Measuring Reactive Power using Phase angle | How to calculate?
Let’s check whether our calculations are correct using the phase angle calculated in the next paragraph.
APPARENT POWER (AP) | How to calculate?
The combination of reactive power and true power. This is measured in Volt Amperes (VA).
Why does this Power Factor this much important? | How to calculate?
Example No. 2
Let’s take device 1 and device 2 which are having same true power consumption but different PFs and calculate their current consumption.
It is observed that increasing the PF of the load decreases the amount of the drawn current from the source to do the same work. Therefore, it reduces the electrical bill also.
Why it is needed to fix the poor Power Factor?
- Poor PF needs more power. Therefore, needs larger cables to draw power.
- To reduce the reactive power penalty fee in the monthly electricity bill.
- To reduce power losses and high heat gains in the power circuits.
- To improve the power equipment’s life. (Like in Transformers)
- To reduce voltage drops which leads to reduce the lifetime of the electric equipment.
Methods of fixing Power Factor
To improve the PF, it needs to add equal and opposite relative power to the circuit. For this, there are three main methods;
- Adding capacitors or capacitor banks (The most common method)
These devices are installed in parallel to the circuit. This is the cheapest method and their maintenance cost is also less. Most of the time Automatic Power Factor Control (APF) Panel is used with capacitors to sense the counter-reactive power requirement and switches between capacitors.
- Adding synchronous condenser
When a synchronous motor operates at no load and is over-excited, then it’s called a synchronous condenser. When a synchronous motor is over-excited by using a DC source it will start to act as a reactive current supplier to the circuit instead of the reactive current drainer. The largest power consumers use this method and it is a very costly method.
- Adding phase advancers
This device is used to improve the PF of the induction motors. It is an AC exciter which is connected to the main shaft of the induction motor and operates with the motor’s rotor circuit.
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