Dear friends

can any one pls share at which temperature of steam turbine rotor can faulty differential expansion probe be replaced?

regards,
ashiq

 

Dear friends,

OEM says it should be done on ambient temperature but i think if it requires only replacing the faulty probe then simply measure the existing gap and install new probe with same gap.

During initial installation or displaced probe due to any reason necessary require the rotor temperature should be equal to ambient temperature.

while this question remain unanswered.
i expect contribution of control dot com members

best regards
Ashique Ali

 

Even the expansion of the probe and holder need to be taken into consideration, so replacing them when the turbine is hot may introduce some unwanted error into the measurement if they are not allowed to warm to the temperature of the surrounding metal/environment.

Replacing these probes is usually best done when everything is at ambient temperature (cool), if only because it may be necessary to shut down again and cool down to ambient to perform another calibration verification check and/or calibration. Best just to do it right the first time than to spend more time and lose more generation to do it again.

I'm always of the opinion that there's only time to do something once so doing it right at that time is very important. I don't subscribe to the thought that there's never enough time to do it right the first time, but there's always time to do it again as many times as necessary. This is typically the thought process of many supervisors and managers who think that if they cut corners and save time on outages they can look like heroes if they don't have to shut down to do the procedure again. And, if they do have to shut down again, well, they took a chance and it didn't work out--better to have tried and failed than never to have tried at all. All of which are just rationalizations for not recognizing what is involved in doing a job and doing it correctly, and for second-guessing the people who do know what needs to be done and how it should be done.

Best of luck!

 

Dear CSA,

Thanx for your contribution. i appreciate your advice. when we shutdown the unit initially temperature was coming down very fast but after two days temperature decrease rate was coming down day by day. so considering the down time it was decided to replace the probe on the 06th day when the rotor temperature was 85 C. if we wait for ambient minimum we need more three days so it was decided to replace the both probes now the unit is working and reading is satisfactory..

My concern was that above ambient any temperature at which this activity can be performed where accuracy is very less affected.

best regards
ashiq

 

ashiq,

One has to do what one has to do--to keep the bean-counters happy. Ultimately, they sign your paycheck, or distribute the funds to compensate you for your work.

It would seem 85 C would be a reasonable "ambient" to perform the work of replacing and calibrating a differential expansion probe. Certainly doing so at 300-400 deg C (for example) would not be desirable, for many reasons, personnel safety being the biggest concern.

 

Dear CSA,

Thanx for your contribution. i appreciate your advice. when we shutdown the unit initially temperature was coming down very fast but after two days temperature decrease rate was coming down day by day. so considering the down time it was decided to replace the probe on the 06th day when the rotor temperature was 85 C. if we wait for ambient minimum we need more three days so it was decided to replace the both probes now the unit is working and reading is satisfactory..

My concern was that above ambient any temperature at which this activity can be performed where accuracy is very less affected.

best regards
ashiq

Dear Ashiq,
This is Ramesh from Zambia. In my power station turbine overhauling is going on. So I removed differential expansion probes for both HP and LP shaft at ambient temperature like 30 deg. So my doubt is while reinstalling the probes how much gap voltage to be keep or I can install sensor by adjusting and matching the DCS value at 0 MM at ambient temperature?

Thanks and regards,
Ramesh R