When would you select a slow start motor

[Lovison]

What are some guidelines or rules of thumb for selecting a slow start motor for pump use? Appreciate any feedback relating to this. Wayne E. Lovison
service-parts@naglepumps.com

 

[buzzp]

I guess your question was about when to select a slow start motor control circuit. Almost any motor can be used in slow start configuration. It is generally the application that determines if a soft start could be used or vfd. Soft starts would often be used if the motor, on start-up, is browning out the power supply causing problems. This also reduces the starting torque so if there is a load on start-up then this torques needs to be considered. Soft starts also dampen the harsh affects of starting a motor, most notably the inrush current which reduces the life of the motor each time it is started. I hope this helps some, if I did not address a specific question please let me know.

 

[Lovison]

Buzzp;

I've also asked this question to the pump engineering people as well. We are entertaining some real long setting pumps of which I'm concerned that an across the line start up would be momentarily delaid by the time the impeller began to turn. So I guess this relates to torque loading and any potential to shear.

We all know that the weakest link in the pump will be most likely the smallest diameter of the shaft. That could be the coupling end or the impeller stud. A breakage between these two points normally is a poor radius design in most cases.

We have a slow start box and it winds up the motor at about 1/2X the rpm and then it goes up to full load rpm. This works well for large motors. But even small motors will see the same result will they not?

My thermal problem (addressed earlier on another thread) was a field wiring problem. The plant had changed out some 100HP motor's and reinstalled new pumps with 75HP motors. It seems they left in the larger 100HP heaters and the system didn't have enough backpressure so the 75HP motor ran out to meet the conditions and the larger heats allowed the motor to fry. Just thought you wanted to know.

Plus is seems that they did not have the motor thermals wired in correctly (if at all) and this would have at least prevent the major motor frying that occured.
















Wayne E. Lovison
service-parts@naglepumps.com

 

[buzzp]

I will follow the other thread. Thanks