I'm not convinced about that. For 2 pole motor at 50Hz, the speed would be 3000rpm. It doesn't look like a machine that is ever intended to run directly off 240V / 50Hz.

The normal definition of base speed is where the back emf equals the dc bus voltage, beyond which the torque starts to fall off and you are in a constant power region. From the max torque curves given that looks more like 18000 rpm. That seems to be what these Germans call the "cut off frequency" and would be 300Hz for this machine. https://www.isel.com/en/mwdownloads/.../link/id/4093/

If you were running with base speed set at 18000rpm / 300Hz / 240V / 3.4Arms phase current, you shouldn't be able to go wrong / toast your motor. Did the motor ever work in your possession? Is it possible you bought a duff, used machine? Did the insulation break down between the windings and the chassis?