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Long Rotor stall time on motor

Long Rotor stall time on motor

Long Rotor stall time on motor

(OP)

I was looking at the motor datasheet for the attached 4000V 350hp motor and was extremely suprised by the stated rotor safe stall time on the datasheet.  

Usually when looking at MV motor datasheets I see safe stall times in the 20-30s range at motor for the hot and cold values but never have I seen stall times as long as these in the 100's of seconds?  

I cant see anything specific about this motor that would allow these long safe stall times so I wanted to see if any of you experts here could tell me the reason.

An extra bit of information:  The motor is a pretty long motor along the shaft axis.  Much longer than most other 350hp motors I have seen.

RE: Long Rotor stall time on motor

You didn't actually attach a datasheet, or give a model number so we could find one ourselves.



 

Mike Halloran
Pembroke Pines, FL, USA

RE: Long Rotor stall time on motor

It's higher than I've ever seen, but this is not a typical motor.......looks like it is designed for starting a very high inertia load.  Since the info comes from the OEM, I'd be inclined to believe it.

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RE: Long Rotor stall time on motor

Motor datasheet looks fine. Verified motor rated torque @1553.8 #-ft. using Motor rated torque =5252*Rated HP/Rated Speed.
A stall time of 83 seconds corresponds to a total driven inertia of 5086 #-fl^2 (I used locked-rotor torque = 141.7 #-ft).
If you got longer starts, you have large inertia in your load.

 

RE: Long Rotor stall time on motor

It says coal mill drive application. Don't they have typically a large starting time ?

Muthu
www.edison.co.in

RE: Long Rotor stall time on motor

Quote:

A stall time of 83 seconds corresponds to a total driven inertia of 5086 #-fl^2 (I used locked-rotor torque = 141.7 #-ft).
1 - Can you explain how you are equating a stall time to an inertia?
2 - If you are looking at an acceleration time, 83 seconds  should corresdpond to 43763 lb-ft^2, right?
3 - Locked rotor torque = 1.417*1554 lbf-ft, right?

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RE: Long Rotor stall time on motor

(OP)
What is it about the construction of this motor that makes it able to withstand these long stall times.

Is the rotor of more robust construction?

RE: Long Rotor stall time on motor

More robust... that would be my guess.... i.e. the primary feature is a more massive rotor to absorb that heat.   I'll bet if you compare motor weight and rotor moment of inertia (both listed on data sheet) to other motors of similar rating you'll see this one has a higher-inertia (larger rotor) and perhaps total motor weight noticeably higher.

We have one set of large motors for flywheel application that has a very massive endring and massive adjacent steel retaining ring which is mostly axially outboard of the endring.

In general I'd guess you can't just increase copper size to reduce starting resistance (and rotor heating) because you need to keep resistance up to keep starting torque up. But there may be other subtle tricks to get the power factor up or perhaps flux density up during start to achieve target starting torque with lower rotor starting current.

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RE: Long Rotor stall time on motor

By the way, the stator definitely would have more a lot more copper to help reduce I^2*r stator heating during start (but can't use the same trick as effectively for the rotor)

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RE: Long Rotor stall time on motor

Also beefy silver-soldered joint between bar and endring.
And perhaps relatively long bar extension distance between core end end-ring to accomodate endring expansion without excess mechanical stress.

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