Type 2 Wind Turbine Generators

A Type 2 wind turbine makes use of wound rotor induction generators, which are connected directly to the WTG step-up transformer.  The stator circuit is similar to that of the Type 1 turbine, with the addition of a variable resistor.  This is achieved by implementing resistors and power electronics external to the rotor; current flow between resistors is implemented via slip rings.  The use of slip rings may be eliminated by mounting the resistors and power electronics on the rotor.  This technique is referred to as the Weier design.  The benefit of implementing variable resistors comes in the rapid control of rotor currents, which results in a constant power output, even during gusting conditions. This also may influence the machine’s dynamic response during grid disturbances.