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Tyre Building Machine Motor - Strange rating plate

Tyre Building Machine Motor - Strange rating plate

Tyre Building Machine Motor - Strange rating plate

(OP)
I have received a 3-speed induction motor used in automative tyre building machines.

The motor name-plate states 5.5/3.5/0.6 KW at 945/555/165 RPM with corresponding currents of 16/17.5/20 Amps, which didn't seem right.

So, I asked the client for the load cycle currents at each speed and he confirmed the ratings as below

Normal Currents
Low speed         20 to 24 A    
Medium speed  8 to 11 A        
High speed        4 to 6 A        
            
Forward to reverse cycle currents (duration 9 seconds each)
Low speed         25  To 30 A for 9 sec
Medium speed  25  To 30 A for 9 Sec
High speed        60  To 70 A for 9 Sec
            
No. of reversals in one cycle of 12 minutes
Low speed         2 times        
Medium speed  1 time    
High speed        4 times    

Questions:

What type of load (torque-wise) that would take such high currents at low speeds ?

And why does the name-plate show lowest KW rating with the highest current ?

The client reports they have multiple tyre building machine motor failures in a year and I am supposed to stop that. !!!  

RE: Tyre Building Machine Motor - Strange rating plate

(OP)
BTW, this is the first time I am doing this type of motor - which goes to prove that troubles always come in small sizes. :)

RE: Tyre Building Machine Motor - Strange rating plate

The efficiency is dropping as the speed drops. Are these three winding motors?

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

RE: Tyre Building Machine Motor - Strange rating plate

(OP)
Yes, Bill. Three separate windings, all connected in wye. (so no possible delta circulation).

RE: Tyre Building Machine Motor - Strange rating plate

As I said, the efficiency is dropping as fast or faster than the speed.
Is this a job for a VFD? If you remove two windings you may have room for one very robust high speed winding.

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

RE: Tyre Building Machine Motor - Strange rating plate

Judging from the kw vs. speed numbers, the continuous torque rating of the motor does not increase much as the speed goes down.  That makes a single speed six-pole motor with about 60N-m torque on an inverter a much more reasonable candidate for substitution.

But the 9 second currents are apparently the result of plugging the motor forward-to-reverse and vice versa and this occurs seven times in 12 minutes.  If I've got this right, this is going to control the sizing of the motor and the drive.

Under the above conditions, I would choose (or wind) a 7kw 8-pole motor and run it overspeed to get the 945rpm.  I would choose a sensorless vector drive with a 1 minute rating at least three times the motor FLA.  If I had the choice, I would use a TENV enclosure for the motor with Class H insulation and, if not practical, go with TEFC with the largest practical fan.

I doubt that a regenerative drive would pay back at this small size so I would go with a full-capacity snubber brake package.  The resistor will need to be right at minimum ohms for the drive brake chopper rating and the resistor wattage will be about 4kw.

I'm sure someone out there will see this differently.  Let's discuss.

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