airgap on large hydro unit

[uhpo]

I got a vertical hydro unit with a 6 meter rotor diameter and an theorical airgap of 15 mm, so i was looking for some IEEE standard that define the tolerances on this airgap between pole face and stator core.
Does somebody know it? i read on some place about 5 % on teorical airgap and on other paper 10% of teorical airgap, so i was a bit confused.

thanks in advance....

 

[uhpo]

the generator is a 48 salient poles one.

 

[wolf39]

uhpo:

To me it makes no sense to specify a certain air gap percentage as an air gap tolerance. High speed hydro generators in the 300 MVA class can have an air gap of about 40 mm whereas the air gap of a bulb generator may be only 8 mm, or even less. An air gap tolerance of plus/minus 10 percent, for instance, is therefore not practical.

Wolf

http://www.hydropower-consult.com

 

[uhpo]

look we are talkign about 15 mm airgap kaplan hydro unit.... and i just wondering the number of the standard that deals with this fact..... or some number from this standard from IEEE.

thnks

 

[wolf39]

uhpo:

The purpose of tolerance figures is to protect a contract partner from unjust liability cases. I remember that for subtransient reactance guarantee figures a tolerance of 30% was specified some time ago as the calculation methods those days were not very reliable. Regarding the adjustment of air gap figures we are in a far safer environment. We therefore should not look for tolerance figures (I don't know of any air gap tolerances specified for large hydro generators by international standards), but to concentrate on ways to improve the quality of dimension measurements.

I know of an OEM which used to specify a rotor roundness of plus/minus 0.6 mm. Such a figure can be achieved by a professional erection crew for your 6 metres rotor and for the stator as well. In reality, however, the erection personnel is under extreme time pressure, especially when the utility is eager to start energy production the nearer the installation is completed. This and contractual bonus clauses can result in negligent working procedures.

There are many cases in the industry where hydro generators are plagued by severe vibration issues since commissioning. As I said in my previous post: To me an air gap tolerance of plus/minus 4 mm for a 40 mm nominal air gap would be unacceptable. For the 300 MVA rotor of 3.8 metres diameter I would even reject a tolerance figure of 2 mm.

Wolf

http://www.hydropower-consult.com