Motor Duty

The S# duty ratings for a motor refer to how a motor will be used. Properly following these ratings should optimize the lifetime of a motor for the lowest machine lifetime expense. (I don't like how that is phrased.) Bearing clearances are a common difference in these motor ratings but it is not the only difference. For instance, a continuous duty motor can have more "play" in its bearings before reaching thermal equilibrium than a short time duty cycle motor.

Yes but there might be consequences to the maintenance requirements and life cycle of the motor...in both cases

Yes for both questions...because you CAN do it, does not mean you SHOULD do it. Depends on the application.

You can use the motor rated for continuous duty in the low duty application. It is made to work at rated output 24/7. The light duty motor will probably have a shorter life, as well as a lower cost for low temperature insulation, cheaper bearings etc, when used in 24/7 service - but it will be cheaper. When it fails you must buy another and you will not have any warranty - not made for 24/7. Continuous duty stuff is made better and costs more. Reminds me of the Chinese cheap socket spanners - the ones that break to avoid over stress on bolts and nuts...

Anything <...can...> be done.

It is a matter of judgement as to whether things should be done and the <...why...> will be the outcome of that judgement.

S4 duty is more stringent involving frequent high currents through the stator windings as well as in the rotor.

Hence, it is possible to use S4 duty motor for S1 and not vice versa.

S1 duty motor if used for S4 duty may suffer rotor thermal damage more specifically.

"300 starts per hour" is 5 starts per minute. That's a start every 12 seconds.

Are you sure that number is correct?

I'm asking because I can't find any data to verify the 300 starts per hour and believe that the number of starts depends on number of poles and wiring of the motor, also.

Yes Mr.lyn.

It is 300 starts per hour as specified in INDIAN STANDARDS INSTITUTION. It is 12 seconds gap between starts. Hence the kick load, and winding temp. effect is considerable when compared to S1 duty, Motor is of constant running, no. of starts per hour is less.

I will try to get the copy of the standards and post here, in 2 days time.

DHAYANANDHAN.S

Key:

P= load t= time PV= electrical losses TC= time of one load cycle Θ= temperature

ΔtD= starting/accelerating time Θmax= maximum temperature attained ΔtP= operation time at constant load ΔtR= time de-energized and at rest Cyclic duration factor = (ΔtD + ΔtP)/TC

The appropriate abbreviation is S4, followed by the cyclic duration factor, the moment of inertia of the motor (JM) and the moment of inertia of the load (Jext), both referred to the motor shaft.

Example: S4 25 % JM = 0,15 kg × m2 Jext = 0,7 kg × m2

In my opinion,if P[S4]=<P[S1] you may use S1 duty motor as S4.The problem is the bearing could be quickly worn out.

The overlapping of the two duties - S1 and S4 - was unsuccessful. I think the present diagram is correct.