Using a softstart on long cables
Using a softstart on long cables
(OP)
Hello
We are wanting to start a subsea electric motor through 3000m of cable with a softstart. This is a marine application so it is ungrounded. The boost transformer (Delta to ungrounded wye) 460:3000 is after the softstart.
Is there a rule of thumb for sizing a reactor that will counter the capacitance of the cable? Would a VFD be a better approach for this? Any problems with a VFD on this length of cable?
thx
We are wanting to start a subsea electric motor through 3000m of cable with a softstart. This is a marine application so it is ungrounded. The boost transformer (Delta to ungrounded wye) 460:3000 is after the softstart.
Is there a rule of thumb for sizing a reactor that will counter the capacitance of the cable? Would a VFD be a better approach for this? Any problems with a VFD on this length of cable?
thx





RE: Using a softstart on long cables
We have some 34.5 kV cable that is about 8 km long. The voltage is more pronounced at this higher voltage but shouldn't be an issue at your lower voltage. We installed a voltage regulator at the load end, but ours is not a subsea application.
Is 3 kV your phase-to-phase voltage? Have you calculated the expected voltage rise?
RE: Using a softstart on long cables
A VFD would work too. The transformer will filter out most of the PWM voltage coming from the VFD.
RE: Using a softstart on long cables
RE: Using a softstart on long cables
RE: Using a softstart on long cables
RE: Using a softstart on long cables
RE: Using a softstart on long cables
Keith Cress
kcress - http://www.flaminsystems.com
RE: Using a softstart on long cables
RE: Using a softstart on long cables
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Using a softstart on long cables
Remember most vfds has parameters that if your using a long leads to the motor these need to set on. Maybe also do a static tune at commissioning would also help.
RE: Using a softstart on long cables
Then added a load reactor that seemed to work initially but is now back to scary, noisy, light dimming starting. Haven't found any guidelines, formulas or help on sizing a reactor for a softstart - just warnings on lengths of cables over ~700m.
Controlsdude - Do you think the result would be the same with a VFD? I think there would be less harmonics so wouldn't be as susceptible to cable capacitance.
RE: Using a softstart on long cables
I have not used a submerged motor like your using but the distance was up to 800 feet. But it was a dry environment. I know cable selection is critical in wet locations and would think a VFD would probably get you out of your problem with soft start. But 700 meters is long distance (~2200 feet)
I know in some applications vfd manufacturers they recommend load reactor + some type of filter.
I would go here and read up some of there recommendations. Maybe give you some idea what the solution could be?
http://www.transcoil.com/Support/Documentlibrary.h...
RE: Using a softstart on long cables
I do find it odd that soft-starters won't work on your system. We have supplied a number of applications over the years where a soft-starter powered a transformer and they all worked fine. Giving the name brands you tried might help determine what is going on.
You have tested the transformer and motor and cables for failures, right?
RE: Using a softstart on long cables
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington