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Retrofitting VFD for a winch for an off-shore oil platform
4

Retrofitting VFD for a winch for an off-shore oil platform

Retrofitting VFD for a winch for an off-shore oil platform

(OP)
We have a 2.5/5.0 RPM rope winch drum driven by a 75 HP, 480 V, 900/1800 RPM (Dahlander winding) two speed motor with 3-stage gearing. The 2.5 to 5.0 RPM speed change is through a contactor and the direction change is through another contactor.

Pic of the winch with the motor below. The cylindrical unit at the bottom left contains the motor and the box above contains the contactors.



We want to have a variable speed option using a VFD for better and smoother start/stop and up/down controls.

The motor will be rewound for VFD duty.

What kind of VFD is recommended for such a winch duty, which will have frequent starts and stops and with a marine environment (saline atmosphere etc.) duty rating ? There are are no mechanical or electrical brakes at the moment. Should the VFD have a braking option also?




Muthu
www.edison.co.in

RE: Retrofitting VFD for a winch for an off-shore oil platform

2
I’ve done similar projects for Navy ship-to-ship transfer winches and a couple of crab boats. Given that your existing setup would have had a mechanical brake, because you would not be braking with a Dahlander motor, you technically don’t need braking in the VFD as a one-for-one replacement. Therefore the best option I would recommend for the environment would be a fully enclosed VFD suitable for NEMA4X / IP65 at a minimum, using heat sinks that are on the outside of a preferably stainless steel enclosure. No air exchange. Then for control and torque accuracy, use one capable of encoderless Flux Vector Control (it’s unlikely that encoders on that winch motor will last).

But for winch duty I would strongly suggest a line regenerative Active Front End drive if you want to relieve strain on your mechanical brake. Dynamic braking using resistors can be problematic in marine environments. The problems with that however would be:
1) Your system, being on a generator, would need to have other motors running off of the bus to absorb the regenerated energy from braking the winch; you can’t push generator fuel back into the tank...

2) Those drives are relatively new and I’m not sure if any of them are designed yet for “fins out” construction. If you can find one that would be ideal.

If those issues prove insurmountable You can try finding custom marine grade resistor banks, by my experience with those was less than stellar. Those were on the crab boats and ultimately, the user yanked them out and went back to hydraulics.

PS: I just re-read your post and see that there are no mechanical brakes? I find that odd for a winch... and thinking through the braking issue, you will need braking anyway because you will likely need aggressive accel/decel profiles to where the drive may not be able to keep up without tripping on over voltage. But any form of electronic braking cannot HOLD a load, that’s why I find it hard to envision NO mechanical braking. Is it a worm drive gear or a tapered rotor?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Retrofitting VFD for a winch for an off-shore oil platform

2
What is the duty of the winch? Like does it do anchor handling, positioning, lifting, or what? Depending on what the winch is used for on the rig may drive exactly how you want to control it.

Also if you do decide dynamic braking is required, a lot of rigs and marine system use water cooled braking resistors, both for space/weight saving and dealing with the marine environment.

MikeL.

RE: Retrofitting VFD for a winch for an off-shore oil platform

(OP)
Thanks Jeff & Mike.

These are mooring winches for jack-up drilling rigs.

Yes, it does have an electrically operated brake attached to the motor free end. Sorry about that.

The client is not looking at regen braking. And no encoder.

Can you suggest good VFD OEM's for this retrofit and a budgetary cost?

Muthu
www.edison.co.in

RE: Retrofitting VFD for a winch for an off-shore oil platform

Rockwell PowerFlex 755 drives offer Encoderless Flux Vector Control and at 75HP can be ordered with a "fins out" mounting option for putting into a SS enclosure. Full disclosure, they write my paycheck every month... but it's what I know best.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Retrofitting VFD for a winch for an off-shore oil platform

(OP)
Thanks again, Jeff. Any rough cost numbers?

Muthu
www.edison.co.in

RE: Retrofitting VFD for a winch for an off-shore oil platform

For India, no. Here in the US for a 480V 125A rated open chassis drive with the flange mount, I/O and HIM, about $15k list (but nobody actually pays list price). I have no idea how that relates to your cost over there.

My boss is leaving today for a 3 week long trip to India because he is helping our team over there. I will forward your information to him, he can get someone to give you a quote.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Retrofitting VFD for a winch for an off-shore oil platform

(OP)
Thanks Jeff. Much appreciated.

My ET signature will lead to my contact info.

Muthu
www.edison.co.in

RE: Retrofitting VFD for a winch for an off-shore oil platform

That's what I assumed. He has it now, I think he will be over there on Monday.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Retrofitting VFD for a winch for an off-shore oil platform

(OP)
If he is in Chennai, I could meet up with him along with our client. Let me know.

Muthu
www.edison.co.in

RE: Retrofitting VFD for a winch for an off-shore oil platform

(OP)
Hi Jeff. Mr Biju Paul from RA India has emailed me and we have talked over phone. We plan to meet tentatively next Wednesday along with my client at Chennai. Thanks for your timely help.

Muthu
www.edison.co.in

RE: Retrofitting VFD for a winch for an off-shore oil platform

jraef,

The older Powerflex 40 in a flange-mount style used a computer-style fan to push air thought the heatsink and we had a lot of problems with fan failures in a 'fins-out' application. Our environment wasn't exactly friendly but it wasn't as harsh as a marine application.

From a quick glance the Powerflex 755 looks to have much the same arrangement. Rockwell replaced the fans under warranty; when the replacement fans also died Rockwell support didn't offer us any hope of resolving the problem so we fitted our own venturi-type airmovers with a fabricated adaptor in place of the fans and that was totally reliable.

Hopefully someone in Rockwell has looked at the design and sorted it out, because the flange-mount drive has so much potential if built properly.

RE: Retrofitting VFD for a winch for an off-shore oil platform

Scotty, yes, that was an issue on the PF40s, they later changed to using bigger heat sinks and no fans on the outside. For the PF750 drives, you either order the Flange Mount version, which comes WITH a NEMA 4X/IP66 fan, or on the Frame 6 and 7 you get a kit that converts a standard chassis to Flange Mount. The kit comes with a NEMA 4X/IP66 rated fan assembly that you use to replace the standard fan that comes on the drive. I had an OEM panel builder working on a Pharma plant next to San Francisco bay that failed to swap them out (probably to use the fans somewhere else?), then the basic fans failed in about a year, prompting call backs for the field service people, after which eventually I get the call. I had to dig into it for about 38 seconds before I found the issue being that the fans were never changed out. It's right there, prominently depicted in the installation diagrams, but hey, who reads instructions?


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Retrofitting VFD for a winch for an off-shore oil platform

Thanks jraef,

I have a long history with A-B's drives going right back to the 1331's and 1336's but the problems with the PF40 tainted my opinion. To be honest it wasn't that the product had a problem, because problems can usually be put right if there's a will to do so - it was the stubborn denial from Rockwell UK that the design was flawed that really irritated me: I wanted a solution, not an endless supply of warranty parts which lasted a month or two then failed and tripped my generators. I'm pleased that the problem has been resolved on the current products because the idea is a winner if it's sufficiently hardened to survive in an outdoor industrial environment. I'll take a look next time we're asked for a field-mounted drive.

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