AC Traction Motor for Marine Use

[YT-371]

Sounds crazy but we are restoring a WWII Navy Tug and it’s DC Diesel Electric system is fried! We are looking into the possibility of adapting an AC traction motor to drive the reduction gear. The 1020 HP Cleveland which is in good shape would drive an AC generator as planned or perhaps turn another traction motor as a generator. Used equipment seems to be fairly priced but we are absolute neophytes and could use some engineering help. Are we crazy? Any help or suggestions would be greatly appreciated.
~Rob
yt-371.com

[John_Perkowski]

Moderator's Note:

Normally, a post about marine vessels would not fly. I've made an exception. Many of us are preservationists in one form or another. Diesels in the WWII era were of a limited number of designs, as the War Production Board controlled significant parts of the American economy.

If there are any locomotive mechanics or electricians out there willing to give technical advice, I think you will find grateful ears. I've gone to their website (http://www.yt-371.com) myself, it's clean and ad-free.

The project is headquartered in El Dorado Hills, CA, and the (munged) email for contact is INFO at YT-371.com

[Rick Rowlands]

An AC traction motor would not be compatible with your control equipment and would require installation of a high priced frequency drive. And if your group is like mine is, you are doing this with little to no money.

When you say that the DC equipment is fried, what exactly do you mean? How did it meet its demise? How did both the generator and motor burn out at the same time? If I had some specific information I could perhaps point you in the right direction. Your equipment may be repairable.

Reply with as much info. as you can and I'll come back with some suggestions.

[YT-371]

An AC traction motor would not be compatible with your control equipment and would require installation of a high priced frequency drive. And if your group is like mine is, you are doing this with little to no money.

When you say that the DC equipment is fried, what exactly do you mean? How did it meet its demise? How did both the generator and motor burn out at the same time? If I had some specific information I could perhaps point you in the right direction. Your equipment may be repairable.

Reply with as much info. as you can and I'll come back with some suggestions.

Hi Rick,
The assumption was that we will need new control equipment. The old DC control equipment is from 1944 and not complete. The motor was running when a salt water head above it let go and you can guess what happened. The generator had been pulled by the previous owner and the armature rewound then was allowed to set in salt spray for several years. All the parts were taken to a rebuilder, baked out and meg checked. The minimum estimate to repair and fix the gen, motor and control system is over $80K if we can find all the parts. When you see used “running when pulled” AC traction motors for sale for 5 to 10 K and only need a control system for one motor, $$$ seem more in line. Yes money matters here but we are committed to get her running. We have the slow turning diesel (1020 HP @ 900 RPM) and the reduction gear which is 4.3:1. We need what goes in between. The prop turns max at 200rpm with normal between 90 and 120. That puts input rpm requirements from 860 on down and cruise at 400 to 500. The reduction gear is non-reversing so the motor must be.
A control system does not need wheel slippage etc. just speed and direction control for one motor. How pricey would such a control system be? We have no idea. It would be nice to have a motor capable of 800 HP when we are done.
~Rob

[Rick Rowlands]

OK what I see as your best bet is not an AC drive but rather to acquire the equipment out of a DC locomotive. The RPM rating of a locomotive generator is close to the engine speed you have. There are four axle, 3000 HP locomotives that are equipped with 750 HP traction motors, that would get you close to your desired 800 HP motor rating. Loco generator driving a traction motor is well proven technology, no need to reinvent the wheel here. Even much of the control equipment could possibly be used, but if not a simple Ward Leonard system will work. Unlike a DC motor, you cannot generate current by spinning an AC motor unless it is a synchronous motor. Also, spinning a DC traction motor would not give you enough juice to turn another motor at full HP due to losses in the conversion.

Before we get to far into this how about providing some good detailed photos of your entire propulsion system. My email address is rick [ at ] todengine.org. One of the largest used locomotive parts dealers is five miles from here, so once we figure out what to use I can help you in the search for the proper equipment.

What you are doing is similar to a project that I am working on, repowering a diesel locomotive.

Moderator's Edit: email addy munged.