Reaktiovoima

Reaktiovoima, the Finnish term for reactive power, refers to the reactive component of electrical power in alternating-current systems. It represents the energy that oscillates between sources and storage elements such as inductors and capacitors, rather than performing net work over a cycle. Reactive power is measured in volt-ampere reactive (VAR).

It is part of the apparent power S, which is P plus jQ, and its magnitude is S = sqrt(P^2 + Q^2). Real power P (in watts) does useful work, while Q accounts for energy exchange with magnetic and electric fields. The phase angle φ between voltage and current defines P = VI cos φ and Q = VI sin φ; equivalently, S = VI.

The sign of Q indicates the type of reactance: positive Q is inductive (energy stored in magnetic fields), negative Q is capacitive (stored in electric fields). In power systems, reactive power is essential for maintaining voltage levels and power factor; too much or too little Q can lead to voltage instability and reduced efficiency.

Control and management: Utilities regulate reactive power with capacitor banks, reactors, and devices such as synchronous condensers and FACTS controllers (for example, STATCOM). These provide or absorb reactive power to support grid voltage, compensate for losses, and improve stability.

Notes: Reactive power does not create or consume net energy, but it increases apparent power and current, influencing conductor losses and voltage profiles. It is managed to keep voltages within specified limits and to optimize overall grid performance.