Ball Mill Super Capacitors

[PieterDen]

Good morning all, I am working at a Copper Concentrator plant in the DRC, we have constant power outages or fluctuations from the bulk supplier SNEL.
We have 4 x 7MW mills that we want to run for about 300sec after a power failure. We have WEG transformers, WEG VSD's and WEG motors on the mills.
The reason for the slow stop that we want is that we have bearing failures on the pinions and the OEM(CITIC) claim that it is due to the sudden stops of the Mills.
Is their any body out their that have done something like this or that can possibly direct me to somebody.
Thank you
Pieter

 

[crshears]

Restarts while full I can understand, but sudden stops while fully loaded? Can you offer more particulars?

 

[Gr8blu]

OP - are the bearing failures on the mill and/or gearbox bearings, or on the motor bearings?
What type of damage is occurring in the bearing?
Are you sure the damage does not happen as result of electric discharge machining of the bearing surfaces (race, journal, housing, etc.) because of the high-energy harmonic content coming from the drives?
Does the loss of power also create a stoppage of the lubrication system for the bearings - or perhaps allow axial thrust to develop?

Whether the mill is loaded or unloaded is irrelevant: it should come down to zero speed in a lot less than 300 seconds.

Question for the mill OEM (Citic): if the sudden stops are the issue, how did they expect to handle repetitive start attempts over the life of the mill, which are also "abrupt"?

 

[edison123]

At 7 MW power, it's most likely white metal bearings all through the drive system. Is it forced lube oil system with external pumps? If yes, you should have a battery operated DC motor lube oil system as a back-up since ac motor driven pumps lose power when the main motor loses power.

Provide more details about the bearings throughout the entire system (motor, gearbox, mill) and their method of lubrication.

 

[jraef]

Ball Mill Super Capacitors​

At 7MW for 300 seconds, you are not going to get anything remotely close to that with "super capacitors"... You can buy what are called "UPD" (Uninterruptable Power for Drives) systems for LV drives that use super capacitors, they will give up to 2 seconds! After that you need batteries, and I have seen those systems that go up to 600A @ up to 480V. But nothing at MV levels.

Batteries for MV drives would be EXTREMELY challenging! Assuming even something like 6.9kV for these (you didn't say), you are looking at around 600A at around 9700VDC... so even using 48VDC batteries, you are looking at 200+ in series, then enough in parallel to provide that 600A for 5 minutes. That's not really feasible.

 

[waross]

Look at the control sequence for a normal stop.
I am sure that you will find that after the power to the main mill motors is removed that the lube pumps continue running long enough to provide lubrication until the mill stops.
Look at a battery powered inverter system to keep the lube pumps running for 300 seconds.
You will save a few millions of dollars.