415v star delta motor how to time 3

[DBates]

I have recently been asked if a 415v star delta motor that drives part of an extraxtion unit can be timed to operate for 5 minutes every hour. If this is possible can anyone please advise. I would have thought that this kind of timing to such a motor may cause more wear to it. I believe under normal circumstances this motor would have been running throughout most of the day. I believe that the motor in question is supplied by three phase and earth.

 

[jbartos]

Suggestion: A motor is designed for certain number of starts in time. Since the HP size of the motor is not posted, please, contact the motor manufacturer tech support for recommendation. Actually, the motor that works periodically gets smaller wear than when it operates with the continuous duty.

 

[aolalde]

5 minutes every hour averages a low RMS load, if the load does not exceed the nameplate current. Starting in Wye connection and Delta- Run; implies a connected load with low inertia.

Check: a) The starting time is less than 3 seconds.
b) The current does not exceed the nameplate.

If so, your motor could work the proposed cyclic load without problem. Verify the steady temperature of the windings after 12 to 20 hours of work; it should not exceed the insulation class limits.

 

[edison123]

S1 duty motors are continous rated while S2 to S8 are rated for intermitent loads (frequent starts with or without load, complete intermitent stops etc.). Pls check the rated duty of your motor. Again, all these duty ratings are made keeping the motor winding temperature as the ultimate deciding factor. So, if you proposed load cycle doesn't exceed the rated winding temp., you should not have any problems.

 

[GordS]

A further consideration is the total number of across-the-line starts. I remember reading somewhere motors are designed for about 5000 total starts. There is winding movement with each start due to the high currents and resulting magnetic forces which can cause reduced insulation life due to abrasion and insulation damage. Starting every 5 minutes will use up your 5000 starts in about 200 days. Now I don't think the number "5000" is hard and fast but I think a reduced life can be expected due to the frequent starts unless the motor was designed specifically for frequent starts as mentioned above.

 

[aolalde]

GordS (Electrical)

The motor works 5 min every hour and starts wye, runs delta. The starting current is reduced to 1/3 of full voltage inrush and the mechanical stress is reduced proportional to I^2. See original post.

 

[jbartos]

Suggestion: Visit

http://www.sea.siemens.com/motorsbu... vs. Aluminum Rotors for Induction Motors.pdf

for 5000 motor starts limit
However, there are motors that exceed this number, e.g. fan motors that are frequently switched by a toggle switch.

 

[ingenieur101]

motors in general has an endless start up time. If you do it the right way, you surely can start and stop the motor at your convinience.

 

[panelman]

without the size it's hard to say anything constructive....

on the other hand, have you thought about adding a VSD?

 

[jbartos]

Comment: The number of motor starts is directly proportinal to the motor quality and a motor principle/type, e.g. better winding insulation, greater manufacturing accuracy, permanent magnet motor versus rotor and stator winding motor, etc.

 

[Marke]

Hello DBates
One start per hour would not be of concern for most motors provided that the starting time was within allowable limits for that particular motor. i.e. if the motor was designed to be used with a very low inertia load, and you started a high inertia load with it, you would expect to have a premature rotor failue.
Thermally, provided that the laod inertia was within the limits for that motor, there should be sufficient cool down period (as I read it 55 minutes) for the motor temperature to remain well below the rated temperature of the insulation.

Best regards,

Mark Empson

http://www.lmphotonics.com