Definition
In an alternating current (AC) circuit, the power that oscillates back and forth between the source and the load without performing useful work, caused by the current and voltage being out of phase due to inductance or capacitance. It is measured in volt-amperes reactive (VAR).
Plain English
Power that sloshes back and forth in an AC circuit without actually doing any work. It's needed to keep magnetic fields and electric fields in things like motors and transformers running, but it doesn't turn into useful output like heat, light, or motion.
Context Anchor
Seen in aircraft electrical system discussions involving AC generators, inverters, motors, and electrical load calculations.
Derivation
From the Latin re- ('back') and agere ('to act'), meaning to act back. The power 'reacts' by flowing back to the source instead of being consumed, which is exactly what reactive power does in an AC circuit.
Why Pilots Care
Aircraft electrical systems must supply both real and reactive power; unmanaged reactive loads can reduce voltage stability and alternator efficiency.
Analogy
Think of carrying a heavy backpack uphill and then back down to the same spot. You did effort, but no net work was accomplished — you ended up where you started. Reactive power is the electrical version of that round trip.
Grounding Statement
In an AC circuit, reactive power is the back-and-forth part of the electrical flow, not the part that is steadily used up to run equipment.
Intuition Check
Do not read reactive power as “responsive power” or “extra available power.” Here, reactive means power that returns back and forth in the AC circuit instead of being fully used as working power.
Example Sentence 1
The aircraft's AC generators are designed to handle both real power and reactive power demands from motors and transformers.
Example Sentence 2
High reactive power from inductive motors required the crew to monitor total electrical load during flight.