An graduate student in electronic engineering

Source text:

Initial studies show that, in principle, variable speed wind turbines can provide a greater inertia effect than conventional synchronous machines, because generator torque can be increased at will, extracting relatively large amounts of energy from the spinning wind turbine rotor. This decelerates the wind turbine rotor rapidly, and so may not be sustained for very long before aerodynamic torque is reduced. High generator torque also results in high loads on the drive train, which may add significant cost.

Source:

Abad, G., Lo´pez, J., et al.: ‘Doubly fed induction machine: modeling and control for wind energy generation applications’ (John Wiley & Sons, 2011)

Writer’s text:

However, this would release the stored energy in the turbine shaft which, in turn, would reduce the rotor speed almost immediately. The resulted extreme mechanical stress imposed on the shaft and driven train would lead to higher manufacturing cost of mechanical parts.

Writer’s comment:

So I sometimes add something to it to make it clearer…. So here it says add significant cost so it is not the cost of the overall thing ,it is the cost of the mechanical parts so I added to clarify and it didn’t change anything because I am sure the author meant the mechanical part. And then here I added the mechanical stress imposed on the shaft and the drive train because here he only mentioned the drive train so I add the shaft as well because there are mechanical stress on the shaft too but he didn’t mention that… It doesn’t change the meaning.