Home

Terms, Units, and Conversions

This Ohms Law Circle can assist with Power Formulas
 
Ohm's Law      
Ohm's Law

Where:
I =  Amps / Current
R = Ohms / Resistance
W = Watts / Power
E = Voltage

Electrical Terms:

  • VOLTS -  ( V or E ) The units of electrical potential or motive force. The force is required to send one ampere of current through one ohm of resistance.
  • OHMS –  ( R ) The units of resistance. One ohm is the resistance offered to the passage of one ampere when impelled by one volt.
  • AMPERES – ( A or I ) The units of current. One ampere is the current which one volt can send through a resistance of one ohm.
  • WATTS – ( W ) The unit of electrical energy or power. One watt is the product of one ampere and one volt. One ampere of current flowing under the force of one volt gives one watt of energy.
  • VOLT AMPERES – ( VA ) The product of the volts and amperes as shown by a voltmeter and ammeter. In direct current systems, volt ampere is the same as watts or the energy delivered. In alternating current systems, the volts and amperes may or may not be 100% synchronous. When synchronous, the volt amperes equal the watts on a wattmeter. When not synchronous, volt amperes exceed watts.
  • KILOVOLT AMPERE – ( kVA ) One kilovolt ampere -  is equal to 1,000 volt amperes.
  • POWER FACTOR – ( pf ) is the ratio of watts to volt amperes.


For those of you that want to know more about Power
The power factor of an AC electric power system is defined as the ratio of the active (true or real) power to the apparent power.

  • Active (Real or True) Power is measured in watts (W) and is the power drawn by the electrical resistance of a system that does useful work.
  • Apparent Power is measured in volt-amperes (VA) and is the voltage on an AC system multiplied by all the current that flows in it. It is the vector sum of the true and the reactive power.
  • Reactive Power, is measured in volt-amperes reactive (VAR). Reactive Power is the power stored in and discharged by the inductive motors, transformers or solenoids.

The reactive power required by an inductive load will increase the amount of apparent power - measured in kilovolt amps (kVA) - in the distribution system. Increasing the reactive and apparent power will cause the power factor - PF - to decrease.

Power Factor
It is common to define the Power Factor - PF - as the cosine of the phase angle between voltage and current - or the "cosφ". The power factor defined by IEEE and IEC is the ratio between the applied true power - and the apparent power.