I am currently in a debate over maintenance stratergies for our dragline generators. You find small ammounts of chatter developing from a generator, what do you do first? I have been told to chalk the comm to clean any blemeshes and burn spots off and been told that SRB's(Surface Rounding Brushes) are a last resort like stoning. I have been told that SRB's are used to clean up small spots of dammage. So if you use them in situations such as high and low spots that are spread right across the comm. surface they can make the lowes lower and the highs higher. What is the best way to reduce the chatter as an interim fix?

Angryman,

I am a Vendor so be forwarned…

It really depends on what you mean by chatter. If GE generators, it probably is a rough commutator. If Westinghouse, the holders are usually in a leading arrangement so chatter can mean either a rough commutator or friction chatter.

SRB’s are meant as a tool and intended to be removed after some time. See the attached file. If you continually have rough commutators, correct brush grades can overcome this problem. Depending on where you are in the world, we would probably have someone to help you with brush selection.

Unfortunately, unless you are able to pull this units for repair, SRB’s may be your only option. If you can shut down for a short time, you can also use some of the hand stoning fixtures available. I would not suggest the ones that are a big handle and you find the biggest guy on the mine site to lean into the comm while you turn the generator. Use one that has a fixture that you set up and run the stone back and forth so that you maintain an even depth while stoning.

SRB_Guidelines.pdf (556 Kb, 25 downloads)

Acklin,

Thank you for the reply.

The advice I have been recieving is from one of your sister companies here in Australia.

When I refer to chatter I refer to the audible clicking of brushes from the formation from a rough commutator. We have identified that we do not have the required house pressure in our draglines and this is being reengineered. That is all well and good but in the mean time I have to keep our generators going, so I am faced with a number of issues, these start and are not limited to extra heat build up, dust build up which brings vibration and streaking of comms. and we are in a climate of no humidity so we have poor film to start with. So in the interim I have to develop a stratergy of treatment to survive until the pressure problems are fixed. Once you notice an audible chatter do you go straight for the SRB's or is there a milder alternative??? I have used chalk to clean up the surface and be sure the brushes are all seated correctly then inspectred the commutator then juged if srb's will help or hinder, or judge if I will lightly stone.
Are there any cases of SRB's making the dammage worse??
Any input would be greatly appreciated.

Angryman,

Glad to hear you are working with our guys in Australia – they will take good care of you. Hopefully, they will put in you in a place less than angry?

Once you hear the commutator noise, you have another option if you think the SRB’s are too aggressive. We have another product called SCB’s (Surface Cleaning Brushes) which are not quite as abrasive as the SRB’s – same construction and principle but you can leave these brushes in. These are really cleaning brushes and are mostly used in contaminated environments. They may help you if you install them early enough. For both products, only one is needed per path.

Have there been cases of the SRB’s making the situation worse – yes, in cases where the commutator is more than 6 mils out of round, the SRB’s are just bouncing around and not able to help. So, if the comm is really far gone, the only options are stoning in place (with a fixture) or pulling the gen.


Regards

SCB's.pdf (147 Kb, 13 downloads)