Our Steam turbine is GE D-11 model.
We have two main stop and control valves (MSCV) (2*100%)
and two Reheat stop (RSV) and Intercept valves (IV)(2*50%)
I want to know what happened to turbine (whenever the turbine is in operation) output in the below conditions or will the below conditions trip the turbine. please clarify me.
MSV 1 closes, CV1 opens and MSV2 opens and CV2 opens
MSV 1 opens, CV1 opens and MSV2 opens and CV2 opens
RSV 1 opens, IV1 closes and RSV2 opens and IV2 opens
RSV1 closes, IV1 opens and RSV2 opens and IV2 opens
open refers to 100% and Closes refers to 0%
We have a facility of Valve Test for checking that the main stop valves are free to close if the unit is tripped and that each control valve is free to close if an overspeed situation occurs.Each main stop valve/control valve pair is tested separately,causing a small allowable pressure rise with corresponding small drop in load. Upon initiating the test procedure, the control system locks out the other valve pair from being tested until the test is complete.
So the above is only during test condition but during the real time operation if the above conditions acted what will be the effect on turbine....
If you were to have a failure of a servo or solenoid that resulted in a single valve closure for the MSV, IV or ISV there would initially be very little change in load (less than during test). However extended operation will cause unequal heating in the steam leads to the turbine and could result in vibration increase.
If you have a failure close of a CV, the results would depend upon you control mode. If you are operating in a pressure governor mode, then the other CV will open to compensate for the increase in pressure (should see this happen during test). If you are in speed governor mode, you will lose the steam flow through that CV and I would expect about a 40% drop in load.
Thank you Very much for your earlier post...
you said whenever one stop valve got closed (becoz of some failure in solenoid or something else), there will be little change in load. but as the stop valve got closed for IV(2*50%) does this not cause steam turbine trip? Because as main steam CV is 2*100% even one closes the other can feed the flow. so still i had a confusion whether one IV closed leads to Steam turbine trip condition or not (during steam turbine normal operation)?
Can you give me a bit more explanation about this..
I need to clarify, I have only seen a poor cutaway drawing of the D11 configuration with combined SV/CV. This design differs greatly than the utility designs I have worked on with multiple CVs.
Reading your reply, I observed that I made an error in the expected response of a SV fail closed. I forgot (can not see) there is not an equalizing header before the CVs. Therefore a SV closure would result in a loss of a CV, thus it would be just like a CV closing.
Do you know if there is or is not an equalizing header after the SVs (before the CVs)
I am surprised if the IV/ISV are only 50%. the units I worked on, these valves were greater than 100% so a closure of one, would allow full load flow through the one open side.
some questions about your unit
when in operation at full load, what is the CVs % open?
when testing the CV (&SV), does the not in test CV open more as the test valve closes to reduce the load drop?
can you test the IV & ISV at full load?
I am seeking clarity in the function of the woobulator. Is this an operator control function.
The wobulator I've dealt with is in place to to make the RPM "wobble" when running the unit at an RPM other than designed RPM (design usually being 3600 or 3000).
For example when starting and warming up a 3600rpm steam unit, it is common for the startup instructions to have a hold point at 3000 rpm. The woobulator (which I believe may be a GE term), varies the RPM constantly (lets say from 2950 to 3050, but I don't know the exact numbers). It does this very slowly though.
I am told the purpose of this is to ensure the unit doesn't remain at an RPM that will cause a resonance to occur in the last few stages of buckets/blades. The unit is designed to not have any resonance frequencies at operating RPM...and other RPM operation is not guaranteed.