Low Generator Field Insulation Resistance

[frequenthinker]

If generator field resistance to ground is low due to moisture, often a welding machine can be connected to the field winding to provide heat for drying out the insulation. We have done this with field removed from generator stator. Any harm in doing this with the field still installed in the stator?

 

[rasevskii]

Well, I will take a bash at an answer. The assumption is that you are using a DC welder. Rectifier type or MG set?

What is the normal excitation current of the rotor compared to the welder that you have? The welder will only put out a fraction of its rated welding amperage continuously, maybe 25 or 30% only. If it is DC then I see no problem in drying out in place. Is this a brushless unit? Observe polarity. Slip Rings? Connect directly to the ring risers to avoid damaging the ring surfaces. Do not inject DC onto the brushholders, as that will burn the ring surfaces, as the unit is not rotating.

Where is Edison123? He can give some more or better tips...

regards, rasevskii

 

[edison123]

rasevskii didn't leave anything for me to cover.

As to the OP's doubt "Any harm in doing this with the field still installed in the stator", none whatsoever. As a matter of fact, I do this only inside the stator in my shop because that pesky powerful magnet has a strange affinity for my tools when it is outside.

But, if I am at customer's site, I prefer to do a short-circuit run of the machine since it is easier, faster and dries out the stator & rotor simultaneously.

Muthu

http://www.edison.co.in