Reactive power, which can be provided by the generators (a device that converts motive power) themselves, does no measurable work but is transmitted back and forth between the reactive power source and load every cycle.
The reactive power like the real power must balance (that is the reactive power produced on a system must equal the reactive power consumed) and can be supplied from the generators, however it is often more economical to supply such power from capacitors (see "Capacitors and reactors" below for more details). In electricity generation, a generator is a device that converts motive power (mechanical energy) into electrical power for use in an external circuit. Reactive power does no measurable work but is transmitted back and forth between the reactive power source and load every cycle. 
