In alternating current circuits, lead occurs when the phase angle of the current waveform precedes the voltage waveform. This is typically caused by capacitive loads in the system, which draw current before the voltage peaks. Power engineers monitor leading power factors because excessive lead can cause overvoltages and instability on the grid.
We have too much lead on this feeder, so bring another reactor online to absorb the vars.
A purely capacitive circuit has a 90-degree lead. Remember the mnemonic CIVIL: in a Capacitor (C), Current (I) leads Voltage (V).
Related terms
Power factor
Ratio of active power to apparent power, showing how much of the current drawn does useful work.
Reactive power
Power that surges back and forth between the source and the fields of inductors and capacitors, doing no net work.
Reactor
An inductive component used to limit fault currents or control voltage on a power system.
Phase
A single distinct oscillating voltage or current in a multi-conductor electrical system.