Representation of variable speed full conversion Wind Energy Converters for steady state short-circuit calculations

Aging material as well as external mechanical and atmospheric influences can cause short-circuits in electrical power systems. The corresponding minimum and maximum short-circuit currents can be determined by performing steady state short-circuit calculations. These values are a design criterion for electrical equipment and at the same time the basis for the dimensioning of the protection devices installed in the grid. The amplitude of the short-circuit current depends mainly on the network topology, the type of fault, the load situation and the number and type of generators in operation. The standard calculation methods have been developed with regard to the physical characteristics of conventional, directly coupled synchronous generators. Consequently, they can not be applied offhand to variable speed full conversion Wind Energy Converters (WECs), whose electric generator is completely decoupled from the grid. ENERCON WECs are based on this design principle and the present paper shows how they can nevertheless be included in the standard steady-state short-circuit calculation tools.