What is meant by power factor?

Answer 1

The cosine of phase difference between the voltage and current...........

Power factor is actually the ratio of the electrical 'true power' that does work in the real world - the 'watts' of power that are converted to mechanical motion, heat etc - compared to the 'apparent power' volt-amps that the meters on the panel seem to show the load as using.

Circuits containing inductors or capacitors draw energy from the supply mains to 'charge' (ie, store energy in their magnetic or electrostatic fields) while the voltage of the sinewave is changing but they return this energy to the supply 90 degrees later. This means they are drawing a current (drawing volt-amps), but not doing useful work with that current, so they're not consuming any true power (watts). An effect of inductors and capacitors is that they move the current waveform out of phase with the voltage waveform. The higher the proportion of stored energy to useful work, the greater the angle between voltage and current.

Pure resistors don't store any energy, so all the volt-amps they draw get used as watts in the load. There's no phase shift between voltage and current, so they're 'in phase'. All the volt-amps are used as watts, so true power equals apparent power, and the ratio of true power to apparent power is 1.0 in a resistor. It has a 'power factor' of 1.0, or 'unity'.

Circuits with inductors (or capacitors), though, draw volt-amps, some of which do useful work (eg, an inductive motor drives a load and heats the cooling air) and some of which is returned to the mains (from the stored magnetic field in the motor windings collapsing). Because some of the volt-amps are returned to the mains, there's less true power than volt-amps - so the power factor is less than 1.0 F'rinstance, a 220 volt motor draws 10 amps at full load, but delivers 2000 watts of power at the same time. It has a power factor of (true power) / (apparent power) = 2000 / (220 x 10) = 0.91

That means 91% of the 'apparent power' - volt-amps - is actually doing useful work - true power. Some places give power factor as a decimal fraction - 0.91 - while others give it as a percentage - 91%. In all cases, though, the angle between the voltage and the current - the 'phase angle' - can be found by finding the angle that has a cosine equal to the power factor. eg, the phase angle in the above example is (cos-1(0.91) or about 24.5 degrees lagging. That's what the answer at the top of this question is saying.

Answer 2

The Power Factor is an indicator of the quality of design and management of an electrical installation. It relies on two very basic notions: active and apparent power.

The active power P (kW) is the real power transmitted to loads such as motors, lamps, heaters, and computers. The electrical active power is transformed into mechanical power, heat or light.

In a circuit where the applied r.m.s. voltage is Vrms and the circulating r.m.s. current is Irms, the apparent power S (kVA) is the product: Vrms x Irms.

The apparent power is the basis for electrical equipment rating.

The Power Factor λ is the ratio of the active power P (kW) to the apparent power S (kVA):

The load may be a single power-consuming item, or a number of items (for example an entire installation).

The value of power factor will range from 0 to 1.

Power factor is the ratio of apparent versus true power. It is the cosine of the phase angle between voltage and current. In a resistive load, the phase angle is zero, so the power factor is one. In a theoretically perfect reactive load, inductive or capacitive load, with zero resistance conductors, the phase angle is -90 degrees (inductive, lagging) or +90 degrees (capacitive, leading) so the power factor is zero.

Answer 3

Power factor is the ratio of a load's true power (expressed in watts) to apparent power (expressed in volt amperes). It is also the cosine of the phase angle, i.e. the angle by which the load current leads or lags the supply voltage.

Answer 4

Power factor is related to the phase angle between voltage and current. It is a measure of the difference between true and apparent power. In a purely resistive circuit, voltage and current will be in phase, and the power factor will be 1. In a circuit with capacitive or inductive reactance, current will lag voltage (inductive) or lead voltage (capacitive). In the worst case, power factor is zero with 90 degrees of lag or lead, and the apparent power will be zero, while the true power is not.

Answer 5

What is the meaning of power factor in electrical terms?

Answer 6

220