AMTK84 wrote:Metra baught the -3S version because they wanted as similar a locomotive to the F40-series units as possible. And they will be one step closer to that when the MP36PH-3S's are rebuilt--they will be rebuilt to have the prime mover run in notch 8 for HEP. Why? Problems maintaining HEP for long periods of time on long trains and vibrations causing all sorts of problems. Main generators and drive shafts are a common replacement nowadays.
Thanks. Whole lotta shakin' goin' on, huh?
![Smile :-)](./images/smilies/icon_smile.gif)
But after doing a little homework and asking around, it seems that fuel economy was the driving force in Metra's decision to go with 3S, because the units as originally ordered could supply HEP via the inverter from notch 3 instead of notch 8, thus providing the dual advantage of fuel savings and noise reduction. The failures of the main generator and drive shafts plus the excessive vibrations could be traced to the aluminum and composite materials used in the construction to keep an already heavy unit from being TOO heavy, but I couldn't find a consensus on that, and is a previously stated opinion that I happen to agree with. Still, it's ironic that they're modifying (or in this case downgrading) these units to provide HEP at notch 8, because that's going to cause more noise and fuel consumption, thus effectively negating the intended benefits, which I'm sure isn't what Metra originally had in mind. Paying the price for cutting corners during construction, I guess.
Meanwhile, other agencies tend to like the 3C version because of the additional horsepower available for traction since the HEP has its own generator, which allows quicker acceleration out of stations and higher mainline speeds. (The 3C units ordered by MARC for instance, have a top rated speed of 108mph, which will be useful since they're going to be operating on certain sections of the NEC. I don't think the 3S is rated quite that fast, but it doesn't really matter since Metra has no routes with max speeds above 79 anyway). I don't know if the 3C version offers the same fuel economy as the 3S, but the quicker acceleration is a benefit that Metra could certainly use on the Rock's suburban branch, which as we all know is a light rail line in a commuter railroad's body. Also, since Caltrain took delivery of these units (to run their 'baby bullet service") right around the same time as Metra did, I haven't heard of Caltrain having nearly the same amount of chronic failures that's still plaguing Metra five years later. However, I'll say that's a bit unsubstantiated, because neither agency has released (to my knowledge) any official figures that show MDBF (mean distance between failures) statistics for these units, which would provide the needed clarity...