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Introduction to the power factor, Part 2a.

In the previous part, we had a look at a general overview of the concept behind power factor, and we used the beer concept to intuitively understand the general behavior of the three types of power. In this part, we will be introducing the phasor diagram which will help us to better understand the concept behind the power factor.

As a first order of this video, Lets’ try to understand the relationship between the voltage and current in an AC circuit. Assume that we have an AC circuit with a voltage “V”, we shall draw this voltage as a straight line vector. Next, let’s assume that there is a current flowing “I” in this AC circuit. We need to keep in mind that the current flowing in an AC circuit has 2 components.

The component which is in phase with the voltage as drawn in the figure, is called the active component, while the component which is 90 degrees out of phase with the voltage, is called the reactive component.

The in phase component of current can be drawn on the same line as the voltage, due to being in phase. Whereas, the out of phase component can be drawn as a perpendicular to the straight line.

We can now draw the current “I” as a vector sum of the two components. The statement is evident by the following derivation. We know that the identity cos squared plus sin squared is equal to one. And hence we obtain the vector sum as “I”. We can also see, that there exists a phase angle between the voltage and current. You must be wondering, where exactly does the power factor fit into this concept. Well, to put it in simple terms, the power factor is the cosine of this phase angle.


For a purely resistive circuit, the power factor will be equal to 1, which denotes the fact that there are no I2R losses in the circuit. On the other hand, for a purely inductive load, the power factor will be equal to zero, owing to a phase angle of 90 degrees.

Practically speaking, a power system always has a certain amount of inductive loads which causes the power factor to vary between 0 and 1. These loads include transformers, induction motors, induction generators and more. We want the losses incurred due to these loads to be as low as possible. Therefore, we always try to bring the power factor as close to 1 as possible. The power factor and efficiency are directly proportional to each other. Hence, the greater the power factor, the more the system efficiency.

In the next part 2b, we will try to understand the power factor using a power triangle and also go into more detail with respect to its significance.

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