in steam turbines 364MW Units equipped with electronic main and back up over speed protection system ,how often should we perform real over speed test.
I suggest checking with your insurance company as a good start. Otherwise once per year or after a major overhaul is quite common. Also if you replace any speed measuring components (within reason)
if the generator breaker was opened while the turbine remained reset, the emergancy governor speed should NOT be reached. The primary governor should control and limit peak speed less than EG trip speed. Now that was true with mechanical and anolog control systems. I don't know if it is true with digitals.
Now for the original question, I would refer to insurance carrier. I really no longer see the need to perform and actual and I recall suppliers use that as a sales pitch. I never saw the need nor pursued an actual speed test of the electronic backup on units with mechancal EG and if customer tested, I knew calibration data was much more acurrate than data taken during actual speed trip
Well, you certainly need to do it at least once to prove that it works. Mechanical overspeed trips were always tested on older machines during commissioning. But it was never something anyone looked forward to.
I'd refer to turbine manufacturer's recommendations, or your insurance carrier, as previously suggested.
Does anyone know where to find the Exponent Report or detailed summary on the Dallman generator overspeed incident? The link at the CWLP site is no longer functional. Thanks
Your OEM-supplied manual should have recommended intervals in it, but I believe that, unless your machine is under any operational restriction, you should carry them out annually. You definitely have to if any part of the speed governor system has had maintenance work performed on it.
Steam turbines with centrifugal overspeed device need to be tested at real overspeed (10% of nominal speed), I've worked with 33, 66 and 135 MW steam turbines. As a back-up, is necessary to test a push button trip, after that one operator is checking the speed ready to trip the turbine with that button if mechanical device doesn't respond. sometimes is necessary adjust it. All emergency trip devices are tested once per year.
Manufacter manual for gas turbines 180 MW pemits simulate that test decreasing the set point, speed sensors are electronic too.
I have been attending meetings where owner is looking into upgrading turbine controls and in every sales pitch for the replacement of the MOST with electronic is "you will never need to perform actual again". So far not one has been able to provide a calculated peak speed for a real emergancy over speed event to conferm electronics works as well as MOST
I'll try to remember to ask specificly tomorrow during Ovation's chance.
