7.3.2   Overspeed testing

 

A 20% proof overspeed test is specified on all large turbine-generator rotors at the time of manufacture.

This allows the rotor balance to be satisfactorily established throughout its operational speed range, thereby providing sufficient margin over normal operational overspeeds caused by electrical grid system disturbances, and the regular 10% overspeeds experienced during overspeed bolt testing. Overspeeding the rotor also proof tests the forging, as it applies centrifugal stress in excess of that experienced during normal operation, thereby providing a quantifiable measure of the margin against spontaneous fast fracture.

 

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