Steam turbines rotor overspeed test

[wayuu1981]

Hello,

Does anyone can tell me if there's any standard or code defining minimum overspeed values to factory test new steam turbine rotors for a power plant (170 MW, 2044psi, 1000F, 3600 rpm):

105, 110 or 120% of nominal speed?
For how long must be maintained this speed?

Thanks in advance for yout help.

Javier Guevara E.
Projects, Mechanical Engineer

 

[byrdj]

I have never heard of any Code or Standard for FAT speed test. I have seen the customers bid spec include such a test.

If I had to spec, the design of the controls should have an emergancy peak speed value. that is peak speed following a full load rejection WITH a 100% failure of the governor valves, so that valve closure is intiated at emergancy trip speed. thus the peak speed is nomally just over 120% rated.

a hold for 3 minutes is what I seem to recall

 

[Mililani]

There are two sorts of overspeed protection, electical and mechanical.

Machanical, a bolt on a spring,the faster you turn the further out the bolt goes , at the setpont tit hits a finger and dumps the hydraulic system closing the stop valve.

An electronic OS system looks at a speed pickup or a tachometer and then trips a solenoid that dumps the hydraulic system.

The OEM should have supplied settings and a procedure for the overspeed test.

 

[JJPellin]

Mililani, I believe the OP is asking about a spin test of a bare rotor. Any steam turbine would have to have testing of the overspeed trip protection system. But, this is not relevant to his question.

I reviewed our specifications for turbines and found no requirement for a spin test above running speed. For large turbines, we would perform the balance at full running speed. We would have a full test of the overspeed trip protection system at the OEM shop and again once the turbine is installed.


Johnny Pellin

 

[stgrme]

All steam turbine and generator rotors (large or small) need to be factory tested at overspeed. My steam turbine-generator specs always include a factory test at 120% of rated speed.

I recommend holding at 120% speed long enough to obtain stable vibration readings. These readings should not exceeed the allowable vibration at rated speed by more than 100%.

For generator rotors, the winding needs to be checked for shorted turns with a flux probe during overspeed testing. For turbine rotors, a visual inspection is necessary after overspeed to ensure no blading or shroud distress occurred during the test.

Best of luck!