GeneralPAC- Making power system intuitive

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In the previous part, we used our previously established knowledge to construct a power triangle which allowed us to understand the relationships between the three types of power and the power factor. In this part, we will look at the root cause behind a low power factor in industrial and commercial power systems, and its consequences.

Before we delve into the root cause, let’s first establish the difference between a leading and a lagging power factor. Simply put, a facility which has more inductive loads shall have a lagging power factor whereas a facility with more capacitive loads shall have a leading power factor. The word “lagging” or “leading” defines the direction of the phase angle between the apparent power and real power.

Expanding upon this, we will recall the power triangle concept. If the phase angle is positive, then it means that it is a lagging power factor. This can be understood when you consider that a lagging power factor consists of inductive loads which supply reactive power to the system, resulting in a positive angle. Furthermore, if we say that a facility has a lagging power factor then it means that the current is lagging behind the voltage by a specific angle defined as theta “θ”

Lagging Power Factor

On the other hand, if the facility consists of capacitive loads, then it would result in a leading power factor. This can be shown on the power triangle with a negative phase angle between the apparent and reactive power. The word leading also signifies the fact that the current is now leading the voltage by a specific angle defined as theta “θ”

Leading Power Factor

Now that we know the difference between a leading and a lagging power factor, we can now move forward with the reasons for a low power factor in the facilities of today.

There is rarely an industrial or commercial facility which is devoid of any inductive loads such as induction motors, shunt reactors, transformers or even induction generators such as wind mills. It is precisely these types of loads which require magnetic flux for performing useful work. This magnetic flux can only be supplied by the reactive power of the system.

Moreover, the magnetizing current required by arc lamps are another cause of a low power factor as they require a high amount of magnetic flux to operate stably.

The greater the amount of inductive loads, the greater the reactive power supplied. And the greater the reactive power, the lower the power factor of the system. You might think how bad can a low power factor be! but truth be told, there are several consequences of running a system with a low power factor.

The first and most important reason is a higher utility cost. This is because a higher reactive power and a low power factor causes an increase in the overall apparent power drawn by the system and subsequently increasing the power demand of the facility.

Another issue caused by a low power factor is the increase in the system losses. A higher reactive power requirement draws more current and the square of current is directly proportional to the line losses. In addition to that, the higher current demand would mean that a larger conductor size would be required to safely transmit power throughout the system.

Line Losses α I2

Furthermore, the increase in the overall apparent power would mean that the KVA ratings of each equipment present in the facility would need to be increased as well. This adds unnecessary design costs to the system which can be easily avoided with a high power factor.

If we consider a generating station instead, then a low power factor would cause higher voltages due to the higher amount excitation current required in the generators to accommodate the additional line losses.

To summarize it all, a low power factor can have long term negative effects on a power system and efforts should be made to ensure a high power factor

In part 3b we will look at some of the techniques which we can use to improve the power factor.

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