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Anonymous Poster #1

Reduction in Overhauling Time of Turbo Generator

07/02/2015 12:02 AM

After de-synchronization Turbine is kept on barring gear for about 4 to 5 days so that the shaft temperature comes down to safe limit of 100/110 degree C and then barring is stopped and Gen is taken for overhaul. To reduce the overhauling period can we stop barring gear intermittently say after cooling shaft below 300 degree C to take out Gen- turbine coupling opposite bolts in pairs say 2 bolts to 4 bolts , then run barring gear for half an hour, for equalizing /redistribution of temperature, again stop barring gear for half an hour take out 2 to 4 bolts..... and so on till all coupling bolts are taken out and finally the turbine is kept on barring gear till the shaft temp. is below 100/ 110 Deg C. This way we can save at least 2 days of overhaul. Some one who has experience of such strategy can help and confirm the actual strategy adopted.Regards
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lyn
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#1

Re: Reduction in overhauling time of Turbo Generator

07/02/2015 12:53 AM

The turbine manufacturer has the experience.

What do they say?
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Yahlasit
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Re: Reduction in Overhauling Time of Turbo Generator

07/02/2015 8:55 AM

You surely can, but you will stress the remaining bolts, scratch the shaft and cause some imbalance.

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RAMConsult
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#3

Re: Reduction in Overhauling Time of Turbo Generator

07/02/2015 3:07 PM

You could, but then you would be violating the entire reason for having the machine on barring (turning) gear, namely uniform heat removal to minimize differential expansion/contraction and dimensional/clearance changes, in all three dimensions.

You haven't said how big the machine is, but if it normally takes 4-5 days to cool down, it's probably 250MVA or more, with HP, IP, and LP turbine sections, with a total shaft length over 100ft, and at least 5 bearing points.

As you know, the higher the steam pressure the higher the temperature of the spindle, and the top quarter of the casings is much hotter than the bottom quarter, so that the instant you stop rotating the shaft the bottom metal will contract and the top metal will expand resulting in the shaft bowing up towards the casing. While the shaft is bending radially it is also contracting axially, placing extreme eccentric loading on the bearings and pulling the end row blading closer to the end bells.

Then there's the eccentric loading that you're going to put on the remaining bolts once you start removing each pair, plus a whole host of other considerations that you appear to be unaware of. If the manufacturer is willing to approve your plan then go ahead, if not then you're writing a script for a disaster.

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pcchatur
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Re: Reduction in Overhauling Time of Turbo Generator

07/03/2015 5:41 AM

Please never attempt. Saving (?) of two days will cost you many more days. FOLLOW THE MANUFACTURERS MANUAL. First, such questions MUST NOT be asked in such forum. Ask the designer who is father of the machine. The process of cooling of shaft system is not so simple. Lot of data generated through calculations, experimentation and simulation and then only the final recommended procedure is made part of Operating and Maintenance manual for the operating agency.
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James Stewart
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#5
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Re: Reduction in Overhauling Time of Turbo Generator

07/09/2015 8:29 AM

Pretty much good advice coming from all responders so far. You are really off your rocker if you think "saving" one day now at a cost of who knows how many days or never if you ruin the machine. These large Steam Turbo-Generators are not toys you can just play with willy-nilly. Who told you this was even remotely OK to attempt?

You need to go back to school, and learn to read the instructions and adhere to them. Apparently, you listen too much to bean counters, or penny pinchers. this is no proper way for a maintenance supervisor, or plant engineer to act.

I cannot castigate or chastise you enough for what you already have done, or are about to do again. WRONG!

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James Stewart (1); lyn (1); pcchatur (1); RAMConsult (1); Yahlasit (1)

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