Editing Power factor (section)

=== Power factor correction of linear loads ===
[[File:Blindleistungskompensation.svg|thumb|Power factor correction of linear load]]
A high power factor is generally desirable in a power delivery system to reduce losses and improve voltage regulation at the load. Compensating elements near an electrical load will reduce the apparent power demand on the supply system. Power factor correction may be applied by an [[electric power transmission]] utility to improve the stability and efficiency of the network. Individual electrical customers who are charged by their utility for low power factor may install correction equipment to increase their power factor to reduce costs.

Power factor correction brings the power factor of an AC power circuit closer to 1 by supplying or absorbing reactive power, adding capacitors or inductors that act to cancel the inductive or capacitive effects of the load, respectively. In the case of offsetting the inductive effect of motor loads, capacitors can be locally connected. These capacitors help to generate reactive power to meet the demand of the inductive loads. This will keep that reactive power from having to flow from the utility generator to the load. In the electricity industry, inductors are said to consume reactive power, and capacitors are said to supply it, even though reactive power is just energy moving back and forth on each AC cycle.

The reactive elements in power factor correction devices can create voltage fluctuations and harmonic noise when switched on or off. They will supply or sink reactive power regardless of whether there is a corresponding load operating nearby, increasing the system's no-load losses. In the worst case, reactive elements can interact with the system and with each other to create resonant conditions, resulting in system instability and severe [[overvoltage]] fluctuations. As such, reactive elements cannot simply be applied without engineering analysis.

[[File:Condensatorenbatterij.jpg|right|thumb|1. [[Static VAR compensator|Reactive power control relay]]; 2. Network connection points; 3. [[Fuse (electrical)|Slow-blow fuses]]; 4. Inrush-limiting [[contactor]]s; 5. [[Capacitor]]s (single-phase or three-phase units, delta-connection); 6. [[Transformer]] (for controls and ventilation fans) ]]

An ''' automatic power factor correction unit''' consists of some [[capacitor]]s that are switched by means of [[contactor]]s. These contactors are controlled by a regulator that measures power factor in an electrical network. Depending on the load and power factor of the network, the power factor controller will switch the necessary blocks of capacitors in steps to make sure the power factor stays above a selected value.

In place of a set of switched [[capacitor]]s, an unloaded [[synchronous motor]] can supply reactive power. The [[reactive power]] drawn by the synchronous motor is a function of its field excitation. It is referred to as a '''[[synchronous condenser]]'''. It is started and connected to the [[electrical network]]. It operates at a leading power factor and puts [[volt-ampere reactive|vars]] onto the network as required to support a system's [[voltage]] or to maintain the system power factor at a specified level.

The synchronous condenser's installation and operation are identical to those of large [[electric motor]]s. Its principal advantage is the ease with which the amount of correction can be adjusted; it behaves like a variable capacitor. Unlike with capacitors, the amount of reactive power furnished is proportional to voltage, not the square of voltage; this improves voltage stability on large networks.  Synchronous condensers are often used in connection with [[High-voltage direct current|high-voltage direct-current]] transmission projects or in large industrial plants such as [[steel mill]]s.

For power factor correction of high-voltage power systems or large, fluctuating industrial loads, power electronic devices such as the [[static VAR compensator]] or [[STATCOM]] are increasingly used. These systems are able to compensate sudden changes of power factor much more rapidly than contactor-switched capacitor banks and, being solid-state, require less maintenance than synchronous condensers.