Blindleistungsproblemen

Reactive power, called Blindleistung in German, is the portion of electrical power that does not perform useful work but sustains electric and magnetic fields in alternating-current circuits. It is represented by the symbol Q and is measured in volt-ampere reactive (VAR); for large systems the megavolt-ampere reactive (MVAr) is used. Reactive power, together with real power P and apparent power S, forms the complex power S = P + jQ, where S = V I and P = V I cosφ and Q = V I sinφ. The phase angle φ between voltage and current determines Q, with inductive loads (such as motors and transformers) producing lagging reactive power (positive Q) and capacitive effects producing leading reactive power (negative Q).

Reactive power does not by itself transfer energy but is required to establish and sustain voltage levels across the network. However, excess reactive power increases current, raises losses, and can cause voltage fluctuations that may affect equipment and limit transmission capacity.

Power-system operators manage reactive power with compensation devices. Fixed or switched capacitor banks provide local VARs; reactors absorb VARs. Dynamic VAR compensators such as static VAR compensators (SVC) and static synchronous condensers (STATCOM) react in real time to voltage changes. Synchronous condensers and carefully rated transformers may also contribute. The goal is to improve the power factor, reduce losses, strengthen voltage profiles, and keep Q within design limits.

Measurement and regulation: utilities monitor Q continuously, and many grids specify minimum power-factor requirements or impose charges for low PF. Reactive power can be controlled locally at generation and load sites, or centrally through grid-scale devices. In power engineering, management of reactive power is essential for efficient operation and voltage stability.