Suitable Starter for Ball Mill Starting Through Slipring Motor 11 kV 2600 kW

Did you consider the slip ring energy recovery ?

VVVF exists for these size motors but the cost benifit ratio you have to consider. Afterall this size of ball mills are not the one that are frequently started and stopped. once started it is likely to run for quite a few months (if not years).

The energy efficient (and hence costly) mechanisms are needed if

a) You want to save energy over a lifetime of the equipment which may be somewhere around say 40-50 starts for your ball mills in its life of 20-25 years.

b) You want a variable speed which is not true in the ball mills.

Note that the starter is a dead investment when the machine (motor) is idle or at full speed.

(1)     Generally LRS is used for Cement Ball mill application. In some process plants LRS / FCMA is also used. Ball mill application is basically constant speed application. Please note that, LRS / FCMA are used with slip ring motor. In slip ring motors maintenance is big problem (wear and tear of brushes, brush assembly, etc). For speed variation if required, then GRR needs to be used, which is not energy efficient and bulky (requires additional cooling circuit). (2)     Considering all above points, now days, for variable speed ball mill, in cement plant industry, it has been started to use MV VFD with squirrel cage motor. It is technically advanced, user friendly, energy efficient, low maintenance and clean solution, in spite the main disadvantage that capital investment is quite more. LRS costs in range of 5-7 lacs. INR however MV VFD starts from range about 1.2 Cr. INR. (3)     For Ball mill starting torque requirement is very high about 70-80%. Pull out torque requirement is also high about 250%. Hence, while specifying ball mill motor, pull out torque is generally given as 250% without negative tolerance. Above said conditions can be met by both LRS and MV VFD. However, selection depends on process requirement (const / variable speed) and cost.

I know it's old technology but for the starting torque required for a ball mill a liquid starter is probably the best option.

Simple and dependable.

Have you considered using a solid stat soft starter? You have to leave some resistance in the rotor circuit to facilitate starting, but you get reliable ramping, near total flexibility and they are typically much much smaller than LR and FCMA style starters. There are many suppliers now who are capable of 11kV solid state starters; Solcon (also sold through Siemens and several others), Motortronics (sold through ABB, GE, Toshiba, Santerno and several others), Benshaw (not sure if they have brand-label partners) and Rockwell / Allen Bradley.

And as I always say regarding FCMA, there is an inherent danger in using a technology that is available from only ONE source in the entire world, even if it so happens that source is close to your country. FCMA is based on a really old old technology that was basically abandoned by the likes of GE, Westinghouse and Siemens decades ago, the people who make it now are the sole source for supply, assistance and repairs.

As I said in my earlier post that, starting toque requirement of ball mill application is high about 70-80%, so soft starters are not appropriate, as it is basically used for reducing excessive torque during starting. In ball mill the starter is required which gives sustained higher torque during it's operation. As you said, your application is fixed speed ball mill with high GD2. Then, use of LRS is right techno-commercial choice. Also, as I said, till recent years people were using fixed speed application for ball mill. However, now a days industry is moving towards use with VFD. In this you can operate your ball mill with it's feed control. If your feed is less you may operate in part load. In which you can have energy saving with use of "Active front end" VFD. If cost is no constraint then, I suggest to have a though over this option, also, if not taken final decision.

Interesting technical paper to read on this subject.

http://www.cimentec.com/uploads/reports/IAS_Experience_with_synchronous_motors_driving_Ball_mils.pdf

Wow HS that was good reading!

I've only worked on 8 ball mills rated between 1500 & 6000 HP but they were all beasts to get started. Watching and listening to a 2500HP motor first start to turn and then slip back as it picked up the load was fantastic! It sounded like it was in agony for the first couple of turns.

With a ball mill I would stick to liquid starters, simple and basic!