Unequal stator core temprature distribution

[arunjohn]

We have two 35MW air cooled, closed type hydro generator.
The first machine with equal core packet height. During full load the core temp is 15°C more at middle than the core ends.(middle of the core is hot compared to core ends top and bottom).
The second machine with varying core packet height. The packet size gradually drecreasing towards center of core providing more air ducts to the middle.
Here the core middle temp is 20°C lower than the core end temp. (middle of the core is cool compared to core ends top and bottom)

Both machines have same type of fans on the rotor.
Core temprature measurements are with Pt100 rtd.
Max. core temp 76°C and min.56°C.

How this temprature distribution on core can be adjusted within 10°C?? and the effect of this temprature variation of core on the key bar or stator frame or class F windings.
Thoughts and recommendations are highly appreciated...
Thank you all in advance....

 

[TonyCro]

hi ya,

Same OEM for both units ?

are you measured on the RTD's embedded within the windings ?

Are the laminations in a good condition, El-CID tested ?

tony.

 

[arunjohn]

Hello Tony,

Yes, same OEM for both machines, (winding RTD's are sandwiched between lower and upper bar), core RTD's are embedded and the laminations are in good conditions, completly new stator...

Arun.

 

[edison123]

The second machine with decreasing stack height towards middle is better and is supposed give an almost uniform heating through out the stack height. (lower core losses in the middle and higher core losses towards the end but the ends being closer to the cold air inlet). 20 deg C temp difference in the second case is odd.

First case is logical since same core loss in all packets but middle of the core does not get good cooling air.

Are the laminations same grade and make in both the cases ?

How are the core stack heights in the second case as you go from the center to the ends ?

Muthu

http://www.edison.co.in

 

[arunjohn]

Hello Muthu,

The laminations for 2 machines were from same vendor, so I guess there is no change in lamination grade..

Please find attached file for core stacking......

I am just thinking about plugging some air ducts at the middle of core, so that the temp. rises at middle and comes more even...Is that a good idea??
How about the core temp. of 70°C - 76°C and its side effects??

Thanks
Arun

 

[edison123]

Arun - From 45 mm to only 20 mm ? Not a good erection plan, imo. I would have chosen 50 mm to 35 mm with less no. of ducts possibly.

Plugging the vents in the middle ? Definitely not a good idea.

Is that 70 deg C to 76 deg C core temp during a no-load run or under fully loaded condition ? What is the inlet air temp at this point ?

Muthu

http://www.edison.co.in

 

[arunjohn]

Hello Muthu,

76°C is at full load operation and if I remember correct,the inlet air temp. is plus 50 °C.

As I thought, increasing the air ducts in middle might cool the core more effectively, but this was way too much cooling at middle. Is there any solution to fix this problem...apart from changing the core??

Does this unequal temp. on core put much stress on key bar, or any destructive effect during long run..

Muthu, what might go wrong when you plug the middle air ducts to increase the temperature..??

Thanks
Arun.