Power distribution systems carry three primary power characteristics.
The first characteristic is the “real power” consumed by the electrical grid. This is the mechanical or resistive loads in the system that accomplishes real work. This is measured in watts and is what most people think of when discussing the power ratings of a given piece of equipment.
A much more nebulous term is “reactive loading.” This describes the inductive and capacitive loads carried by the distribution grid. Inductive loads are those caused by the formation and subsequent collapse of magnetic fields. Capacitive loads are those characterized by the charging and discharging of capacitors in the system. Capacitive and inductive loads connected in parallel will act to minimize the effect of one upon the other due and as a result, will cancel each other out. This is because in a purely inductive circuit, the current sine wave will lag behind the voltage sine wave by 90 degrees while the reverse is true in a purely capacitive circuit. If we perform some complex math (literally, as it involves imaginary numbers) we’ll discover that the capacitive loads will cancel out the inductive loads. The term for the opposition to current flow caused by these components is called reactance.
The final type of load distribution characteristic to be discussed is system apparent power. This is normally only used within system design to determine loading limits. It describes the overall energy consumed by a system that is both utilized by loads and dissipated to the environment.
The overall system efficiency can be determined by calculating the “power factor” of the system. This is a trigonometrically calculated value described by taking the cosine of the angle between the real power and apparent power. This angle is referred to in electrical engineering as the impedance angle as it is a function of the overall impedance (a term describing the combination of resistance and reactance.) The closer this number is to 1 or “unity” the more efficient the circuit is.
If there’s any interest, I’ll do the derivation and math behind all of this in another segment. It ranges from simple trigonometry to differential equations.