First a short introduction: (the question is below the first image).
The capability of fault ride-through of wind turbines is the most important requirement related to national grid codes. Based on that, wind turbine should remain connected to the network during various scenarios of fault grid to maintain the system stability. 
The figure below is an example voltage profile for which a wind power plant must be able to keep up production if the voltage in the point of connection is above the red line.
A single line diagram for a single wind turbine connected to the grid is shown below. According to information received from the turbine manufacturer, it can supply the required fault-ride-through current if the short circuit capacity from the grid, at the LV side of the turbine generator is higher than 3 times the nominal current for the generator. The requirement is not related to relay tripping.
I can't see why this is a requirement, and how it can be relevant for the turbine's FRT capabilities.
Why does the turbine/converter require a short circuit capacity of 3xIn in order to supply the needed FRT current? Is it the frequency converter that requires this current?