hi there,

anyone has any experience in balancing steam turbine-generator? Just wondering if you can share your experience and procedure in doing it? for example, how long should we wait before we can take 1xTS and phase as reference/trial/trim run? how long does the whole balancing process would normally takes?

we just had a high vib trip on our 700 MW turbine (after major overhaul). vib during FSNL was normal (around 50 um/pk-pk) but as the load increase to 450MW, our LP 2 and generator bearing shootup up to 200um and tripped on high vibration. unfortunately we dont have any vibration analyser installed. so cant do much from vibration analysis point of view. any idea on what can cause it? I'd appreciate any opinion. thanks

As you say that you dont have any vibration analyser installed so how can you tell that what happened to the machine.

It could be a broken or loose blade which can imbalance the rotor and can also excite the blade pass frequency.

There are a lot of reasons, please share the online vibration data...->

This sounds like a case for a competent consultant. 700 MW should be worth some money to you.

I have to agree with Bill, it sould like you need to get someone in, I used to balance both steam and gas turbines, this sounds more likly to be a thermal expansion problem or a rub or even a generator thermal problem, all of which is going to take a consultant in who is set up for this type of work to sort it out.

A 700 MW turbine is an expensive bit of kit, get the experts in.

Chris

I am with Chris, on the surface it sounds like a rub, not a balance issue. If it was balanced at FSNL, then balancing further probably won't help much...

Get some expert assistance...

I totally agree with you guys. We are currently trying to get service from an expert. meanwhile, we're still trying to find anything abnormal during loading period.

how much temperature difference would we see in a generator if there is a thermal expansion problem? All trending plots are in the attached file. Dont see any abnormality with generator slot temperature and bearing metal temperature. anyone can see something from the trending? it would help me a lot. thanks

U2_Trending.pdf (108 Kb, 16 downloads) Trendings

hiz,
Like it was mentioned the best approach would be someone who knows how to do it. The complete set of vibration readings from all available bearings needs to be gathered and evaluated where the problem is located. Most possibly the rotors are running in second mode and as such two plane balancing is required. In your case the machine needs to be brought back to normal operating range and run until amplitudes and phase angle are stable. In order to add the weight the entry needs to be done to LP casing and it takes many hours until conditions are such that someone can enter it. As a last resort the weight can be added to couplings but it’s not advisable unless no other options are available.
In the past when I was balancing 220 MW TG’s usually it was taking the whole weekend (two runups).
Good luck but like it was mentioned it sounds fishy to be simple unbalance.
Alex