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Understanding Alternating Current AC and Phase Angle

What is Power Factor?

Power Factor is the cosine of the phase angle between current and voltage. Power Factor is the ratio of true power to apparent power.

Three Basic Circuits or Loads

  • Resistive
  • Inductive
  • Capacitive

Or Any Combination

  • Resistive inductive
  • Resistive Capacitive
  • Inductive Capacitive
  • Resistive Inductive Capacitive

Or Any Combination

  • Resistive – Incandescent Lamp Resistance heat
  • Inductive – Motors – Contactor Coils – Relays (coils)
  • Capacitive – Capacitors – Start Capacitors – Run Capacitors – Power Factor Correction Capacitors

What is Power?

Power is measured in Watts

Volts X Amps X Power Factor = WattsWatts only equals Volts X Amps when the Power Factor is 1 or unity.Most of the time the Power Factor is less than 1.

  •  Power = Watts : True Power
  • Volts X Amps = VA : Apparent Power

Power Triangles vs Right Triangles

To understand more three sides of right triangle. The article is about classical geometry.
For the baseball term, click

[su_label type="info"]Pythagorean expectation.[/su_label]

The following graphics are introduction of Right Triangle, Power Triangle and Power Factor Traingle.

Right Triangle for Resistive Inductive Capacitive load

The next graphic is resistive, inductive and capacitive load in right triangle diagram. Inductive and Capacitive are in reverse direction or 180 degree different.

Main Inductive Loads in Your Plant

Induction Motors

Low power factor mean higher load  current than necessary and accompany higher line losses. Inductive loads are the main cause of low power factor; with induction motors the main contributors. Under operating condition a motor may often be operating underloaded due to or more of the following reasons.

  • While making selection of even for a standard motor, it is generally not possible to exactly match the rating of the machine with the load. The motor may have some reserve capacity.
  • User may select a slightly larger than machine to ensure safety.
  • When selecting a machine for more critical installations, the number of derating for all unfavourable operating conditions are assumed to be occurring at the same time. This result in selection of an oversized machine.
  • Wide voltage fluctuation may be prevalent in a rural distribution system, particularly in developing countries. In such cases it is normal practice for users to select a oversized machine for their needs.

The power factor of a motor decreased sharply at load lower than rated. See more detail and table of % Efficiency and Power Factor corresponding to values at full load.

[su_label type="info"]See Induction Motors[/su_label]

[su_label type="info"]See 10HP Induction Motor case Reduce Waste Energy  by Improve Power Factor[/su_label]