6.6 kv. Large Variable Speed Motor "Eating brushes"

[jammyjim]

hi

Just after some fresh ideas on this problem, got 3 of these machine running large freshwater pumps for some reason recently they are going through brushes very quickly, a new set was put in last week 144 brushes, and there already showing signs of major wear, also sparking a fair bit not massively but noticeable I'll post more nameplate details tomorrow.

Brushes are of correct grade, motor current is fine, machines are paired with their own regulators, they are all matched up with right regulator, they haven't been mixed n matched, all connections on motor/brush gear/regulator are good.


Thx

jammyjim

 

[Skogsgurra]

Slipringed motors? Not DC Machines with a commutator?

This is very interesting and I have a hunch. Are the sliprings only for start? Or is it a doubly-fed machine? Seen similar phenomena in large wind turbines.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jammyjim]

No slip rings, and it's purely An AC machine, the sator is just a standard 3 phase winding 6.6 KV nothing complicated,the armature just looks like an armature from a DC motor visually, but I think the internal windings are very different, the brush gear has 36 brush arms each holding 5 brushes, all the leads from the brushgear go to a regulator which has 6phases I'm no expert on the regulator side, I think it's old school technology 1970 ish I was in short pants then

But inside the regulator there is another 3phase stator winding and 3phase rotor winding, I think the rotor turns inside the the stator to increase the speed somehow, had the covers off the regulator to inspect it, and it all looks fine.

 

[Skogsgurra]

The plot tightens...

I know of several machines that *could* fit your description. But I can't make the "no slipring" statement compatible with "brush consumption" AND "AC machine". What kind of beast is this? Pictures? Nameplate?

Any manufacturer?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[theode]

Sounds like an "ac comm"motor,or a "Schrage" motor.
The brushgear is adjustable to obtain the variation in speeds.
There are 2 windings on the armature.
Supply to the slip rings,induces voltage to the armature winding,through the brushes to the stator winding.
The movement of the brushgear alters the phase angles to give the speed.
Its complicated to explain without diagrams.

 

[jammyjim]

Thx for the replies, I'll be uploading some pics later, btw it's a Laurence Scott motor

 

[Skogsgurra]

Theode, then it is probably a Scherbius machine. They have the regulator outside the motor itself - just as the OP says.

BTW, I saw several Schrage motors only a few weeks ago. They seem to survive in textile applications.

OP: Were they running well up till now? Or have they been "sleeping" for a few years and then started again? Other (higher) load?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jammyjim]

https://www.dropbox.com/s/c2sotkhh1mwhizt/2014-09-12 09.34.59.jpg?dl=0

<---- motor nameplate

https://www.dropbox.com/s/siwakf3i52wnc4p/2014-09-12 09.35.29.jpg?dl=0

<---- motor

https://www.dropbox.com/s/pxtrtkym7uftq83/2014-09-12 09.36.51.jpg?dl=0

<---- rugulator nameplate

https://www.dropbox.com/s/efue2ymj8lswu6s/2014-09-12 09.36.14.jpg?dl=0

<---- regulator

 

[jammyjim]

Motors have been running for years, nothing much has changed, the load on them is pretty constant, but the last few months they have been going through brushes very quickly, really odd

 

[theode]

Is the commutator ok? Not in need of undercutting?
High mica segments can cause excess wear.
Just a thought.

 

[Skogsgurra]

That's a very good thought - but after almost 40 years, I don't think that they haven't done this many times already.

Still, that's all I can think of. Next step would be to do a detailed check of "Everything"

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Compositepro]

Has any silicone sealant been used around the motor?
thread237-343881

 

[waross]

That would be my suggestion also. The fumes from curing RTV silicon are deadly to brushes. Has silicon been used anywhere where the fumes can reach the motor.

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