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Steam turbines rotor overspeed test

Steam turbines rotor overspeed test

Steam turbines rotor overspeed test

(OP)
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

RE: Steam turbines rotor overspeed test

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

RE: Steam turbines rotor overspeed test

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.

 

RE: Steam turbines rotor overspeed test

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

RE: Steam turbines rotor overspeed test

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!

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