Generator continuously at partial load

[rotw]

Hello,

I have a question regarding a synchronous AC generator (pilot exciter type) driven by a turbine, the generator is rated/sized for 60 MW but will happen to operate most of the time (about 95% of the year) at 35% of it rated capacity (approx 20 MW).

The question is what are the consequences in terms of :

- efficiency
- lifetime, premature failure of electrical and mechanical components, mechanical issues
- overheating
- others?

Fron view point of good/sound enginering practices and codes are there any objections to proceed with such design ?

thanks in advance.

 

[electricpete]

I have a question regarding a synchronous AC generator (pilot exciter type) driven by a turbine, the generator is rated/sized for 60 MW but will happen to operate most of the time (about 95% of the year) at 35% of it rated capacity (approx 20 MW).

The question is what are the consequences in terms of :

- efficiency
- lifetime, premature failure of electrical and mechanical components, mechanical issues
- overheating
- others?

There are no objections to operating an electric generator at low load that I know.

There is also the prime mover. If it were reciprocating combustion engine it might not like operating at low load. Steam turbines not a problem. Not sure about gas turbines. If you are concerned about the prime mover perhaps give more details.


=====================================
(2B)+(2B)' ?

 

[ScottyUK]

Agree with ePete, I can't imagine the generator will experience any detrimental effect at 35% load. The windings will operate well below normal temperature, but warm enough to avoid any problems. Effciency will be a little lower because of the shaft-driven fans are designed to move sufficient air to extract I²R losses when operating at 60MW and they are a constant load.

A steam prime mover will be probably ok at 35% of capability but won't necessarily be happy if load drops further to about 20% or less because of inadequate cooling and premature condensate drop-out in the final stages of the LP turbine. A diesel will not operate well at 35% load. A gas turbine will be well below its full-load efficiency, and if you use the exhaust to raise steam the HRSG will struggle without auxiliary firing, which will further decrease the efficiency.

 

[rotw]

ok thanks a lot guys for the input.

 

[waross]

I have had a lot (20+) of small diesel generators on standby service that normally ran at 30% or less of rating. These would be residential and commercial units, most less than 100 KVA. The extra capacity was required for starting A/C units. A couple of the installations had issues with the diesel pumping lube oil out the exhaust at light loading but we never had any issues with the generator ends as a result of light loads.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

Hello rotary dubya,

What speed does your alternator rotate at?

Salient pole or smooth rotor? For salient pole machines windage losses become a significant portion of total input energy at that low a loading...

And I wouldn't drop the prime mover considerations that quickly...

What's the prime mover?

Plus, nobody mentioned hydraulic turbines...

Pelton wheel machines would likely still be very efficient at 1/3 of rated load.

Francis turbines could and probably would suffer significant cavitation damage at that loading; so would Kaplans...and due to having to have their scroll cases vented they would likely exhibit poor efficiency / utilization of water. Deriaz units would probably be fine.

 

[NCTHAI]

IF the prime mover - turbine is gas turbine, there will be significant impact on the efficiency of the machine. Gas turbine efficiency is very low at low load. As all members of has told, generator will not have a problem to run at low load.