Question About motor starting

[Cryodude]

Our cust specify that our pumps need to start under an 80% voltage condition so we size our motors acordingly. We manufacture Cryogenic pumps for the LNG market so we are talking submersible applications. We are starting to question the start torque curves provided to us by the manufacture. Example We started a 1100 Kw @ 6600V 12 Stage pump with a 36% volatage drop in less than 2 seconds. So according to calculations we started this large pump @40% available torque in under two seconds. According to the Motor manufacturer the
The temp effects on the motor reduce the available start torque by at least 30% at 0 speed they give us a modified torque curve based on this idea. So if there calculations are correct shouldn't we see an increase in start time with the voltage drop of that magnitude.

 

[dpc]

It's difficult to believe that you can accelerate an 1100 kW motor to full speed in two seconds. What is the normal speed?

Torque varies with the square of the voltage. But a centrifugal pump requires very little torque at low speed because it isn't pumping anything.

Reduced-voltage starters provide as little as 50% voltage to the motor and the motor generally starts OK as long as torque requirements at low speed aren't too high.

 

[Cryodude]

Thank yoy first for answering
The spee dof the pump was Either 1800 RPM or 3000Rpm I will have to look it up The start was DOL but do not get me started on why we were seeing a 36% voltage drop. Bad engineering on power providers side.