At what speed does the Mecc Alte underspeed protection cut in?

[merryengineer]

At what speed does the Mecc Alte under-speed protection cut in?
What happens when this occurs?

[wellandpower]

Mecc Alte under-speed protection cuts in at 10% below the nominal speed (so 1350RPM for a 1500RPM unit and £1620 for an 1800 RPM unit).

When this happens, in order to protect the alternator, the AVR cuts the current to the exciter, reducing the machines voltage and output.