Jump to content

Maximum Number Of Starts


Recommended Posts



I have an ABB motor 250 KW 4 poles with star/delta starter connected to a flywheel.

The motor runs idle for about 1 hour every 2/3 hours. Can I turn off it without problem during the idle periods?

The question in general is: What is the maximum number of start (starts/h) for this motor?


Thanks in advance,



Link to comment
Share on other sites

Hello dodicaro


Welcome to the forum.


I would suggest that you confirm the number of starts per hour rating with the motor supplier, but would be very surprised if it is less than one start per hour.

The big issue is the moment of inertia of the flywheel and how long it takes to start.

Every time you start the motor, there is a severe overload during start and you dissipate the full speed kinetic energy of the flywheel in the rotor. This causes a lot of heat in the rotor and if the rotor is not designed to absorb that energy, you will cause premature failure to the motor.

In addition to determining the number of starts per hour, you need to determine the maximum start time, or the maximum load inertia that the motor can start. If both of these criteria are met, then you should be able to stop and start as required.


One additional issue however, is that the use of a star delta starter places extra stresses on the motor, couplings and drive system due to the very high transient that occurs during the transition from star to delta. (see http://www.lmphotonics.com/star_delta.htm) Every time you start the motor with a star delta starter, you are subjecting it to this transient and doing some damage which will shorten it's life. You can minimise the damage by ensuring that the open period between the star contactor opening and the delta contactor closing is in the order of 0.5 - 1 second. Otherwise, look at using a soft starter.


Best regards,


Link to comment
Share on other sites

Dear Domenico,

I've seen a similar - but different - question on another italian forum.

If inertia is not so high, I think that you can switch-off the motor running for one hour in idle state.


I agree with Mark and with his suggestions.

Best regards



Mario Maggi - Italy - http://www.evlist.it - https://www.axu.it

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...