Who never wondered which symbol to use for reactive power?
You can find in brochures, technical papers or even on display of monitoring equipment all the possible combinations: KVAR, kVAr, or kvar for example.
And the question is: which symbol should be used, in order to comply with existing standards?
Generally, people remember that the symbol for volts is “V“, with regards to Mr. Volta, and the symbol for amperes is “A“, with regards to Mr. Ampere.
It is then logical to have the apparent power S, which is the product of voltage by current, symbolized by “VA” (voltampere).
For active power P, it was decided by the Electro-technical Community to use the same unit, (watt) and symbol as the mechanical power, i.e.: “W“, with regards to Mr. Watt.
For reactive power Q, it was decided to introduce the letter “r”. Even if the unit of reactive power is consistent with VA, the International Electrotechnical Commission (IEC) proposed the symbol “var” (with small letters).
On the other hand, the symbol for kilo (103) is k, and the symbol for mega (106) is M.
Then, the multiple of “var” are kvar (kilovar) and Mvar (megavar).
There is also often some confusion concerning the symbol of electrical energy.
The unit of energy is the quantity of energy obtained by dissipating a power of one watt during a period of one second. This unit is called one joule, the symbol is “J“, with regards to Mr Joule.
In electrical engineering, a very practical unit has been introduced, representing the dissipation of a power of one watt during a period of one hour. The unit is then Wh (watt hour), product of power by time.
The multiples are kWh (kilowatt hour) and MWh (megawatt hour).
For reactive energy, the corresponding symbols are varh (var hour), kvarh or Mvarh.
All the details can be found in IEC 60027-1 (“Letter symbols to be used in electrical technology”). The same symbols are also used in IEEE documents, such as IEEE 519 (“Recommended practices and requirements for harmonic control in Electrical Power Systems”).