Statics (electrical engineering)

A stable operation of AC networks to organize, in which it is electrical engineering at power generators , the setting of a static , English droop used. The statics characteristic describes the negative slope of the standardized characteristic curve f (P) or U (Q). This represents the function of the setpoint value of the active power P of the frequency f represent respectively the the reactive power Q of the voltage U .

The value of the droop σ is therefore the quotient of the frequency deviation at nominal power compared to idling and the nominal frequency:

${\displaystyle \sigma =-{\frac {\frac {\Delta f}{f_{n}}}{\frac {\Delta P}{P_{n}}}}}$

Frequency and voltage statics

A droop is a linear regulator characteristic that describes the behavior of a generator set as a function of network parameters such as voltage and frequency . It is used in the network operation of many power plants to coordinate the primary control of active power P and reactive power Q via the network variables as an information carrier.

The active power P is regulated as a function of the network frequency f, for example by increasing the torque and thus also the power in a turbo generator with a decreasing network frequency and vice versa. The grid voltage U flows into the reactive power control as an input variable. The reactive power output Q of the synchronous generator can be set via the level of the excitation current . A static connection is used when a PI controller is combined with a reactive or active power-dependent, linear influencing of the setpoint.

gradient

Base load power plants have a high statics, peak load power plants a low statics. A low droop means a flat f (P) characteristic, i.e. H. Even the smallest frequency deviations lead to large load change reactions.

In addition to the statics, the gradient g of the change in performance is also used to describe the system behavior . This representation is equivalent, but describes the inverse P (f) or Q (U) function in real power per Hertz or reactive power per volt. The product of gradient g and static σ of the power frequency control always gives the numerical value 200 in 50 Hz networks. In DA-CH, a value of σ = 5% or g = 40% / Hz is common for decentralized generation plants.

literature

• Alfred Engler: Applicability of droops in low voltage grids (PDF file; 898 kB). International Journal of Distributed Energy Resources, Vol 1, No 1, 2005.
• Adolf Schwab: Elektroenergiesysteme , 3rd edition, chap. 15: Frequency and voltage maintenance, Springer, Berlin, 2012.

Individual evidence

1. ↑ droop of a set. In: International Electrotechnical Vocabulary. IEC, 1986, accessed February 11, 2020 .