A Design Load Case (DLC) is a combination of environmental conditions with operational conditions or other design situations (such as assembly or maintenance) that a wind turbine might encounter during its life time.

When designing a wind turbine, it is a common practice in the industry to perform numerical simulations of different design load cases to ensure that the structure will withstand any situation it might encounter.

Design load cases are often divided into design situations, which are then subdivided. Some examples of design load cases taken from IEC-61400-3-1 (2019) are

DLC 1.2 : the first digit ( 1 ) refers to the design situation, which in this case is Power Production . This means than any DLC 1.x will refer to a situation in which the turbine is producing power. In particular, DLC1.2 aims at reproducing the normal operating conditions of the wind turbine
DLC 2.1 : DLC 2.x correspond to the design situation Power production plus occurrence of fault . in DLC2.1, a loss of electrical network is simulated
DLC 6.1 : DLC 6.x correspond to the design situation Parked . In DLC 6.1, the turbine is idling (i.e. the blades are pitched, the rotor is rotating very slowly and the turbine does not produce any poewr) and the environemntal conditions correpsond to an extreme storm.