Actually, are you sure about the second part of your statement, that the trolley wire will be changed to 480VAC? Because of only two possible current conductors (trolley wire and rails) that would have to be single phase, and will take goody sized capacitors on the car to smooth out the ripple.

Modern day industrial inverter drives begin by rectifying the incoming AC to DC, then using high speed semi-conductors to feed pulses to three output lines to mimic three phase AC. These are variable frequency drives; the speed of the switching can be varied so the output frequency varies from maybe 6 to 400 Hz (cycles per second). The rotational speed of the three phase induction motors just follows the frequency.

It would really be to their advantage to leave the trolley wire at 600VDC (a typical value for the DC bus in a 480V inverter) and feed the DC bus directly. That would eliminate the ripple problem on the DC bus, and leave the overhead compatible with the other trolleys.

I'm just making a guess, but I'd speculate that the original sentence should have read "An inverter mounted inside the car will reduce trolley wire voltage and change it to AC current for the motors." I did a double take on that too, but I'm guessing wire voltage will remain 600 volts DC.

Yes sorry about the wording on that sentence. What Frank Hicks said is what I meant to say. All the other cars on the system have 600vdc traction motors so the wire voltage will not change in the overhead.

Phil Randall
Kaufman TX.

This looks like an interesting adaptation of newer technology to an older vehicle. What horsepower are the motors? We have a pair of air compressors at work, 40 and 50 HP, with motors that look about that size (eyeballing things from the size of the wheelset and axles). The 50 HP unit is brand new, and has an inverter drive; speed ramps up and down with air consumption. Really sweet machine-

What I like about the motors pictured is the cast frames and cooling fins. My old boss used to call them 'mill duty' motors. They should work well in streetcar service, and look like they are an off the shelf commercial item, which should make replacement easy if one goes bad.

At various times in the past, railways and electrical manufacturers have experimented with 3-phase electrifications. There were a few here in the US, and I think the longest lasting system was in Italy. The big drawback is the overhead contact system (to use the modern term); it has all the complications of trolley-bus overhead, only at a much higher voltage. I recall one traveler's account of a European electric line that had synchronous motors and may have been the Italian system mentioned above. The locomotive would start up and then run at either 18.5 mph or 37 mph (about 25 or 50 kmph), locked into the AC frequency. The part that the traveler found annoying was that his carriage had a flat wheel, and the flat spot clatter would be at an unvarying tempo all--night--long.......

Since we've wandered away from the original topic to that of re-powering streetcars with modern industrial motors...

While it's not really preservation, it would allow the "living history" aspect to not consume every spare part in the world, so I suppose it has its place. Here's a couple thoughts that come to mind looking at the pix, without any further knowledge of the project.

Industrial three phase induction motors come in three main varieties: Open Drip Proof, Totally Enclosed Fan Cooled, and Totally Enclosed No Ventilation. The ODP motors allow air to flow through the windings to cool them; also rain, leaves, litter, mice... you get the idea, not at all suitable for our purpose. TEFC motors have a closed case, with a shaft driven fan to blow air over it. TENV motors are designed with enough thermal mass to cool by convection alone, and typically have big heavy cases with lots of cooling ribs.

I see a fan shroud on the end bell of the motor in the photo, so I'll assume it's TEFC. There is a problem with running TEFC motors on inverter drives... the motor relies on it's shaft speed for cooling. Running the motor under load at slow speed ensures it isn't getting adequate cooling, much to the detriment of the motor. The way around this is to use an external fan to force ventilate the motors, but that adds another layer of mechanical complexity. It also adds a background of constant blower noise that doesn't belong with a traditional streetcar.

Railway motors tend to have bigger bearings than industrial motors, for good reason. One half the weight of a railway motor is "unsprung" weight, with no cushioning what-so-ever between the motor case and the steel wheels. Every time the wheel clatters through a frog, the effect on the motor is going to be the same as picking it up and dropping it. Industrial motors are not designed for this service. I sure hope they bought motors with sleeve bearings, because I would expect ball bearings to "Brinell"; the balls beating little dents in the bearing races the same as a Brinell hardness tester does to the test specimen. When this happens the bearings will have very short lives.

Looking at the photos again, I see a Zerk in a clearance hole in the fan shroud, so I'll assume they are sleeve bearings, but that points out another problem. Grease lubed sleeve bearings normally have a pipe plug opposite the Zerk, which is meant to be removed before the bearing is greased, so the new grease can expel the old. Failure to remove the plugs during greasing leads to the motor case and windings being pumped full of grease over time, which isn't a good situation. Unfortunately, that pipe plug would be located against that steel plate, opposite the pillow block they are using for an axle cap bearing. I sure hope some thought was given to continuing lubrication and maintenance.

Great summary, Dennis. Very informative.

What puzzles me about the above project is why they didn't simply go with DC motors. You can buy a new 600 V railway traction motor right off the shelf.

Here's one: http://www.alibaba.com/product-gs/22787 ... ction.html

[Edit: A 500 kW motor like this one is surely too powerful. But I suspect you could find a smaller one.]

Are they going to do anything to lubricate the drive gears and keep them clean? It doesn't appear to me that there is much space provided for a gear case on that truck.

The motors on this car are 40hp which is a little bit more power then we need, Savannah did a similar conversion with 60hp motors but found that it was a little bit to much power for what they needed and has been re powering there cars to 30hp motors, the truck in the photos is near completion and should hopefully be installed under the car some time soon. One of the reasons we are playing with these systems is to reduce over all maintenance time required on these cars, not just on the motors but also on controllers and other systems on our cars, we operate 365 days a year in daily transit use "these cars see a lot of wear and tear" and this system will be designed to operate and feel the same while out on the line as a solid DC car while eliminating many hours spent on general maintenance.

The comment about motor bearings in an industrial motor vs. those in a purpose-designed traction motor is right on the money. Industrial motors are designed to sit on a nice stable base connected to Mother Earth and their bearings are sized accordingly. Traction motors have comparitively huge bearings because they take a beating from the transmitted shocks and vibration through wheels and axles.

One of the well-known trolley rebuilders tried this same approach with industrial DC motors a few years ago and it did not turn out well. Thus one might anticipate the same results from this current application.

To expand upon Mr. Hamley's comments, MUNI, the nation's largest operator of "standard" streetcars in daily service, save for New Orleans, is doing quite the opposite of MATA, in that they are finding ways to use original motors and controllers on cars that see daily service.

MUNI is having Swiger Coil of Cleveland, OH rebuild K controllers with new insulating material. The company is also doing motor work for the Pennsylvania Trolley Museum.

PTM Member Bruce Wells has a report, as part of his irregular, but informative "Weakly Reports," found here:

http://www.weaklyreports.net/Weakly_Reports/Entries/2012/3/17_CLEVELAND_ROADTRIP_TO_SWIGER.html

It should also be pointed out that the car MATA is "experimenting" with, did not surivive into preservation with its trucks or motors, and probably not the controllers, so they aren't scrapping out historical fabric to conduct the test. I imagine that if the test with the AC motors does not work, they can always go back to the tried-and-true DC traction motors.

Yes they have made enclosed gear cases for these trucks. These photos were taken a year ago. I passed by the barn the other day and it looked like the project was further along. The three phase AC motors were cheaper than rebuilding an old DC traction motor is what I was told. Also they are fitting resilient wheels to this car.

The trucks that are being modified for Dallas 754 were originally under a Melbourne MMTB Y-1 class car. Only four Y-1s were built in the late 1920s. They were a lightweight car built to the Peter Witt design. The cars were quite handsome but were not liked by the motormen (easy to convert to 1 man operation might be their thinking). Couple that dislike with the onset of the Depression and no more were built. There is one remaining car with different more modern Melbourne trucks under it.