Large Motor Starting for mine applications : Guidance required

[Ashdgee]

Good day fellow engineers.First of all ,let me say I'm happy I have come across this forum.

Although I have 5 years experience in engineering design , substations , motor controls etc , I have been presented with a problem I have never worked on before.A client , a mining company wants to install two Winders of 22MW each and one Ball Mill of 36MW. I have worked on water treatment and oil and gas projects where the largest motors I have worked with is 880kW.I bhave never worked with such large MW motors.

What are the best methods of starting such large motors. Althogh Im trying to gather as much info from the internet as possible, I thought i might hear from some experts here , especially those who are familiar with such. I would welcome any advice , from some typical motor power/control schematics if you have ,,any previous project case studies, any useful links that may help me to start familiarizing myself with such large MW motors.

From what I see, in most cases ,most of these are not induction but synchronous.Please guide me on some design tips for these.

Appreciate your help.

 

[waross]

One solution is wound rotor motors with liquid rheostats in the rotor circuits.
The low speed torque capability of a wound rotor motor is effective in starting loaded mine mills.
The application was two times 3000 HP motors driving each mill.
Induction motors work and play together much better than synchronous motors.
The total HP on the mill floor was 36,000 HP.
PF correction was achieved with synchronous condensers.
For motors of that size, the motor manufacturers will be glad to provide advice and examples of similar installations.
Some other mine mills being constructed at about the same time were using synchronous motors to drive mills.
Special techniques were used to allow two synchronous motors to share a common gear driven load.

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

 

[LionelHutz]

You more or less start them like you would start any other large motor.

It might surprise you how often ATL/DOL starting is used on very big motors. Sites like that have their power delivered directly from transmission lines so there are few constraints, such as voltage dip, they are worried about.

Primary reactor starting is often used. It's a fairly simple and reliable means of limiting the current and mechanical shock to the motor.

We've built soft-starters for motors over 20,000hp before. This is more current than voltage limited.

A line commutated inverter can be used for a synchronous motor if the field can be applied at any speed. This requires a brush type motor or a motor with a rotating transformer brushless exciter. Really on necessary if speed control is needed.

Possibly wye-delta starting could be used. Typically, this can cause so rather nasty torque transients during transition since it wouldn't be a closed transition version of this starter type.

 

[crshears]

If I understand it correctly WRIM have for some time been configured / equipped with solid-state choppers that use high-speed switching to virtually eliminate the losses associated with liquid rheostat starting/speed control, with the energy of said switching returned to the line more or less regeneratively, at least according to a textbook I've been in possession of for more than a few years...

Winders are positively and negatively accelerated repetitively and frequently, and as such their motors could well require independent constant-speed cooling fans to cope with such severe duty cycles. Robust and properly rated starting and control equipment is therefore required, no matter the type of motor ultimately chosen.

Supplying utilities such as ours are often subjected to wildly fluctuating voltages due to the severe real and reactive power draws of such large motors, and if both a mine and its supporting community are at the end of a longish transmission supply circuit or two the community often suffers from these.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]