Rotary scew motor overload possibilities? 1

[SteveKW]

I know I have little data to go with but I am interested in the posible causes of motor overload when attached to rotary screw compressors.
I understand that they are positive displacement compressors and restricting the discharge would increase the load to the motor.
What other possibilities are there to cause an overload?

PS
This is a brand new motor that has just replaced an older motor that also began to run overloaded!
50HP
206 volts 3 phase
91.2 eff
138.5 amps nameplate
149 amps running.

 

[JJPellin]

We have seen two types of overload problems with screw compressors. Both of them ended up being the same basic problem; fouling. The compressors I am referring to are dry screws with timing gears to maintain a fixed separation between the screws. In a dirty service, a built up of salty material when running filled up the clearances between the screws and to the case. When the compressor was shut down and an attempt was made to restart, the motor would overload at startup and trip off before it could get up to speed. After water washing to remove the salts, the compressor would start normally. It is unusual in our business, but a dirty machine actually moves more gas than a clean one.

 

[SteveKW]

Thank you.