VFD start current
VFD start current
(OP)
I just realized that the vendor is using a thermal-magnetic breaker to feed a VFD/Motor application rated at slightly above 125% FLA. Looking at motor starting curve Vs breaker curve, it seems pretty tight. My question is, what would be the maximum starting current drawn by a 753 Powelflex? Could that ever be as large as the motor starting current? I'm at a position where I can use a larger size breaker/cable, but wanted to know if that's even a concern. Thanks in advance for your help!





RE: VFD start current
Motor current, when frequency is controlled WITH voltage, can be very significantly lower than if started Across-the-line (DOL), in fact the VFD is able to make the motor put out 100% FLT at 100% FLC, no other starting method can accomplish that. VFDs are quite frequently used as glorified soft starters for that very reason.
"Will work for (the memory of) salami"
RE: VFD start current
RE: VFD start current
VFD: Powerflex 753 rated for 40 HP motor (52 A)
Motor: 40 HP, 46 FLA, 306 LRA
Breaker: Type HFD 3070, 70A
The AB representative confirmed jraef's statement: max of 200% of FLA during motor start, which would not trip breaker even if motor start lasted for more than 10 seconds. Are there any good documentation I can read regarding this operation?
RE: VFD start current
Lots of learning resources on VFDs out there, try searching on "VFD tutorial".
"Will work for (the memory of) salami"
RE: VFD start current