Maximum number of starts per hour

The manufacture would be the place to find out. Not knowing the service factor of the motors and the loading it is only a guess.

We have motors (larger) that we allow 3 starts per hour. All motors over 250 hp are limited to 6 starts an hour. Per manufactures specs.

You might also check your inverter specs. I have seen speed drive models where you use the normal duty version for 'typical' applications, and you use a heavy duty version for the severe starting applications.

I have seen the same for solid state soft starters.

This was for products in the AltiVar and AltiStart series, which you may very well have 'over there' because the catalog had voltage like 400V and

690V listed as well. I don't know if my catalog was branded Square D or what but I think they would probably trade as Telemecanique there. j

The inverters are ABB.

OK. All I'm saying is that, if you're looking into the maximum number of starts per hour for your motors, you might want to check the same 'rating', or intended application, of your inverters. Sorry I can't help on the actual question you posted, about the motors themselves.

j

I'd be surprised if they allowed even six. IIRC, most motors of that size are limited to only 2 starts in three hours, or one restart if it was already up to temperature. Some really large units are limited to one start in 3 hours (these are MW range though).

Of course, it depends too on the type of 'start'. A 'soft start' of an unloaded motor from a static inverter system might be very 'gentle' to the unit and be allowed any number of times. Also, if they had forced cooling (separate fans or circulating water). Or unusual insulation class...

As always, the manufacturer would be the best place to start. But also look into the inverter design. 'Soft start' or VFD may be a lot more tolerable. (especially centrifugal pumps that have very low torque requirements at low speeds).

daestrom

Wrong wrong wrong all.

A VFD can start the motor at 100% FLA. Starting restrictions are based upon Across-the-Line (DOL) starting, where the starting current will be 600% FLA. Using a VFD means there are NO RESTRICTIONS to the number of starts per hour, other than those imposed by ramp settings. That is true for both the drive and the motor.

Soft starters are another thing all together. The Starts-per-hour rating of the motor stays exactly the same. Some soft starters, and ESPECIALLY that Telemecanique piece of junk mentioned earlier, are so cheaply built that they can take FEWER starts per hour than the motor they are connected to. There are many brands that are built to exceed the starts ratings of their motors, but that is not one of them. You need to ask that question when selecting a soft starter, but many people don't bother.