Why there is a Power factor in Electrical Power?

Answer 1

The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power.

By definition, the power factor is a dimensionless number between 0 and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source on each cycle. When the power factor is 1, all the energy supplied by the source is consumed by the load. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle.

The power factor is determined by the type of loads connected to the power system. These can be

Resistive
Inductive
Capacitive
If a purely resistive load is connected to a power supply, current and voltage will change polarity in phase, the power factor will be unity (1), and the electrical energy flows in a single direction across the network in each cycle. Inductive loads such as transformers and motors (any type of wound coil) generate reactive power with current waveform lagging the voltage. Capacitive loads such as capacitor banks or buried cable generate reactive power with current phase leading the voltage. Both types of loads will absorb energy during part of the AC cycle, only to send this energy back to the source during the rest of the cycle.

For example, to get 1 kW of real power if the power factor is unity, 1 kVA of apparent power needs to be transferred (1 kW ÷ 1 = 1 kVA). At low values of power factor, more apparent power needs to be transferred to get the same real power. To get 1 kW of real power at 0.2 power factor 5 kVA of apparent power needs to be transferred (1 kW ÷ 0.2 = 5 kVA).

It is often possible to adjust the power factor of a system to very near unity. This practice is known as power factor correction and is achieved by switching in or out banks of inductors or capacitors. For example the inductive effect of motor loads may be offset by locally connected capacitors.

Energy losses in transmission lines increase with increasing current. Where a load has a power factor lower than 1, more current is required to deliver the same amount of useful energy. Power companies therefore require that customers, especially those with large loads, maintain the power factors of their respective loads within specified limits or be subject to additional charges. Engineers are often interested in the power factor of a load as one of the factors that affect the efficiency of power transmission.

Answer 2

As a mech, I am confused by this concept also. But, here is the best explanation I could find for someone like me:

"the Power Factor is an indication of the efficiency with which electricity is being consumed. It was stated that the Power Factor varies according to the type of equipment used by the respective organisation and that it depends on how such equipment is used. A high Power Factor shows that electricity is being used efficiently, whereas a low Power Factor demonstrates a poor level of efficiency."

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Answer 3

Power factor is related to how a current waveform compares to the voltage waveform for a given load. Most loads are some combination of resistive, capacitive, and inductive.

Resistive (R) loads allow the current and voltage to remain synchronized with respect to the same time interval ... hence there's no "power factor" (or the power factor could be called unity).

Inductive (L) loads tend to put the current waveform "behind" the voltage waveform. This means they draw more power from the utility than is actually required for the process (an induction motor is a good example of this).

Capacitive (C) loads tend to put the voltage waveform "behind" the current waveform. This means they also draw a different power from the utility than required for the process.

Knowledge of the load characteristics (R, L, C) is required to adequately size the supply and incoming connections.

Answer 4

In industrial plants, the advice is to limit power factor to 0.95 only.This is because when capacitors are connected to motor terminals for power factor correction, the terminal voltage rises higher than the normal line voltage during a brief start-stop or jogging operation. The motor windings get overheated and in some instances may result to burning of windings.

Answer 5

Basically it is the ratio of power being supplied to a device compared to how much it uses. You usually see it used with motors and VFD's (Variable Frequency Drives) because the while speeding up or slowing down the motor the magnetic field around the motor can actually cause power to go back on the lines that are trying to feed it. So the cause is basically the inductive loading (magnetic field) of motors on the circuit. I think that is the best I can explain. I would go to wikipedia for more in depth description.