ES44C4 GEVOS and their ilk

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Posted by Erik_Mag on Tuesday, July 16, 2019 1:08 AM

Overmod

 'll let Erik explain the induction of back EMF in wound-armature motors, but note that a good locomotive induction motor has essentially none, meaning that the maximum synchronized rotational speed of the motor is determined only by characteristics of the modulated field current, and for a synthesized AC drive this can be relatively fast without counter-losses related to speed.

Back EMF in a motor can be thought of as the equivalent of the back pressure provided by a piston during the power stroke of a piston engine (energy equals force times distance moved). In essence, the back EMF is an inherent part of the motor converting electrical energy to mechanical energy. This simplest in case of a DC motor as there is no phase shift between the voltage and current.

Back EMF for AC motors is a bit more complicated as it provided by the field (from field windings or permanent magnet) in the case of a synchronous motor or the slip between. The proportion of electrical power that is converted to mechanical power is the proportion of the current that is in phase with the applied voltage - hence power engineers reference to real power versus reactive power. An unloaded induction motor will draw current from the lines, but the current is almost 90 desgrees out of phase with the line voltage, hence little real power is transferred to the motor.

FWIW, inverters do have to be designed to handle the reactive power needs of the motors, mostly in a higher current rating than what would be expected from a resistive load of the same power.

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Posted by Leo_Ames on Tuesday, July 16, 2019 1:09 AM

I was under the impression the C4's were considered versatile machines, at least in comparison to modern DC motored C-C power like SD70M-2's or ES44DC's. Equivalent or better performance to a ES44DC, yet no concerns about short time ratings and such on a heavy drag freight when mixed in a consist of more capable six motored AC power.

Obviously a less capable machine with less tractive effort, but one that's still better able to blend in on something like a heavy coal train up a grade in a pinch than an ES44DC or Dash 9 could.

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Posted by CSSHEGEWISCH on Tuesday, July 16, 2019 6:42 AM

BNSF is apparently pleased with their performance as they have taken delivery on Tier 4 locomotives from GE with the same arrangement.  They also have a small batch of SD70ACe-P4's with a similar setup.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
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Posted by zardoz on Tuesday, July 16, 2019 11:31 AM

Leo_Ames
Obviously a less capable machine with less tractive effort, but one that's still better able to blend in on something like a heavy coal train up a grade in a pinch than an ES44DC or Dash 9 could.

Agreed.

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Posted by YoHo1975 on Friday, July 26, 2019 2:09 PM
You don't often see a solid block of C4s on a drag freight of any kind in either case. It's usually amongst a bunch of 6 axle units. BNSF also put DC traction on all sorts of trains that no other railroad does. So, in the context of BNSF's trains are they different from what they're replacing? Sure, they aren't as versatile as 6-axle AC...but BNSF wasn't giving you those in the first place. Also worth noting that UP (at least up till now) will regularly throw in SD70Ms on trains going over Donner. (though I almost never seem them on the massive trains headed to Roeper or Bailey) Those DC units mixed with assorted AC units seem odd to me. All I can imagine is that they've over powered the train enough that those units won't limit the train.
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Posted by timz on Saturday, July 27, 2019 12:44 PM

YoHo1975
UP (at least up till now) will regularly throw in SD70Ms on trains going over Donner.

No reason why not, assuming the train's speed won't drop below ... guess a DC SD70 will be perfectly happy at 12 mph, won't it? I'm guessing most UP trains are doing better than that on the steep part, above Gold Run.

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