Why are horizontal turbogenerators hydrogen cooled? 3

[McTaggart]

Can someone please summarise the advantages of using hydrogen as a cooling medium for high speed turbines, and perhaps give an indication of any efficiency differences between hydrogen cooled units and water/forced air cooled units?

Thanks

 

[dpc]

From Standard Handbook for EE (Fink & Beaty), Section 7:

Heat transfer capability of H2 is 1.51 times that of air. (Thermal conductivity is nearly 7 times that of air).

Hydrogen reduces windage losses which are proportional to gas density.

Hydrogen reduces insulation oxidation and reduces fire hazard.

My version of Handbook is old (like me), 11th edition. But I'm sure newer versions would have this info as well.

Hope that helps.

dpc

 

[electricpete]

Sounds like dpc had it covered. Although I hadn't heard the one about fire hazard reduction.

You mention hydrogen and water-cooled like they are two different animals. They can certainly be both (I work at power plant with two 1250MW hydrogen-filled generators with stator cooling water system.

I think the general progression of the "optimum" design as power increases is:
air cooled
hydrogen cooled
water and hydrogen cooled.

The air cooled ones are probably least efficient and also least costly. Water/hydrogen cooled on the other end of spectrum. As power increases naturally the optimum economic choice will direct you to pay more up-front for improved efficiency.

 

[McTaggart]

Thanks for the quick replies.

Could either of you hazard a guess as to the percentage increase in efficiency of hydrogen vs non-hydrogen cooled units?

 

[electricpete]

I also remember hearing the terms "direct cooled" and "indirect cooled." I'm not sure the difference but perhaps direct cooled means that there is a water cooling system to cool stator directly (like ours), and indirect cooled means the water cools the hydrogen. (not positive about that).

My guess regarding efficiency wouldn't be worth the pixels it's printed on. Perhaps there is some info at the ge page:

http://www.gepower.com/dhtml/publications/en_us/index.jsp/

 

[busbar]

Peter--that link is a goldmine. Dare I suggest, start at GER3688b if you don't have a generator backgound. GE has made internet publishing like it should be.

 

[electrageek]

My experience comes from working for GE as a field engineer installing and starting up large Generators. In addition to all the good points covered by the people who responded I would add that the increased power generation capabilities make hydrogen attractive as well. A 20MVA rated generator as an air cooled unit can be up-rated to 29MVA if filled with 30psi of hydrogen. That means the same amount of iron, copper, insulation, etc can now produce an additional 9MVA. Normally the GE Generators are rated at 0.5 psi, 15 psi, and 30psi.

 

[jwerthman]

"Direct-cooled" and "Indirect-cooled" refers to the hydrogen path in the rotor. With indirect cooling, the hydrogen flows through gas paths in the rotor forging and heat is removed from the field windings by transfer through the conductor insulation to the rotor steel and then to the cold gas. With "direct cooling", the hydrogen gas flows through ducts in the conductors. Heat transfer is directly from the conductor to the gas.