magnetic wedges against efficiency

[uhpo]

Hi
I got a little problem with the efficiency of 4 MW genset, it´s hydro, and 600 rpm so 50 Hz, and in the design it comes without magnetic wedges, now it is needed to rewind, so i was thinking on get more efficiency with magnetic wedges, cause i´m supposing the iron losses will decrease, cause in the old design we have higher losses on iron than we expected.
ok, i wait for your always important help

 

[edison123]

Magnetic wedges are mainly used for reducing the pole face losses in salient pole machines. Quantifying those losses before and after (magnetic wedges) though is a toughie. They also help in reduction of magnetising current.

Muthu

http://www.edison.co.in

 

[electricpete]

In the motor repair world, the standard motor repair specifications (like EPRI 1016679) instruct that wedges should be replaced like for like (magnetic for magnetic, non-mag for non-mag). I don't know the exact reasons, but I can guess.

My thought would be not to authorize is unless you have reviewed the design very carefully for adverse effects. I'd think that installing magnetic wedges should tend to increase the stator leakage reactance. That can adversely affect the stability and the voltage regulation. Can decrease short circuit strength which might affect protection strategy. For motors it may affect starting performance but you don't care about that. They also can vibrate out if not installed correctly.... not as much a concern if stator is vpi'd.

That is the risk side of the equation. There is also the benefit side. Muthu indicated there is not as much improvement in losses from mag wedges on salient pole as on smooth-rotor designs.

Just my thoughts fwiw.

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(2B)+(2B)' ?

 

[uhpo]

but how to quantify this losses, cause you´ll see them on the iron, so how to diferenciate it´s like hysteriesis and foucault losses how to split them

 

[edison123]

uhpo

If you have the money, time and highly accurate instrumentation for very low power-factors, you could do a before and after (mag wedges) kinda stuff. I would definitely talk to the OEM before you do such costly experiments.

pete - it is other way about.

Muthu

http://www.edison.co.in

 

[starkopete]

This isn't exactly on point but it is some interesting reading on magnetic wedges in a motor.

Thanks

 

[wolf39]

uhpo:

We need more information to efficiently help you.

Assuming a salient-pole machine, the pole face losses can be quite high if the generator air gap is small and the stator slots are wide. The main portion of these pole face losses may originate in the massive pole end plates. It therefore would be most economical to replace only the end wedges by magnetic ones. Assuming a total iron loss of about 20 kW, I'd guess that the pole face loss portion at present is about 2 to 4 kW in total, depending on the air gap. So you may gain a mere 1 to 2 kW after installation of magnetic wedges, which tend to brittle. Is this worth the risk? Also, in case you want to compare the iron losses before and after rewind (with magnetic wedges) you have to perform a minimum of two calorimetric loss tests (windage and iron). Quite time consuming and costly.

What's the air gap, the overall stator core length and the stator bore diameter? Is it a salient-pole machine?

Wolf

http://www.hydropower-consult.com

 

[motorspert]

How old is the machine? You may find a modern insulation system allows more copper to be used and this would be more beneficial than the mag wedges. Its difficult to quantify without knowing generator details. Why the need for a rewind? IS the core ok?

 

[wolf39]

uhpo:

Let us have a response to our comments and questions in case they offered "important help" to you.

Wolf

http://www.hydropower-consult.com