In electrical circuits the current is in phase with the voltage when we are in presence of resistors, whereas the current is lagging if the load is inductive (motors, transformers with no load conditions), and leading if the load is capacitive (capacitors).
The total absorbed current, for example, by a motor is determined by
vector addition of:
1. IR resistive current
2. IL inductive reactive current
At these current are linked to the following powers:
1. active power linked to IR;
2. reactive power linked to IL.
The reactive power doesn’t produce mechanical work and it is an additional
load for the energy supplier.
The parameter that defines the absorption of reactive power is the power factor.
We define power factor the ratio between active power and apparent power:
cosϕ decreases as the reactive absorbed power absorbed increases. Low cosϕ, has the following disadvantages:
1) High power losses in the electrical lines
2) High voltage variation in the electrical lines
3) Over sizing of generators, electric lines and transformers.
From this we understand the importance to improve (increase) the power factor. Capacitors need to obtain this result.