Greg, I am also interested in just exactly how a 3-phase induction motor can be converted into a generator. I never really looked into it, but I am under the presumption that railroad locomotives use dynamic braking by converting the traction motors into generators, and the output is completely dumped across huge ballast resistors, thereby making the motor (which is now acting like a generator) look into almost a dead short circuit. I think most locomotives use AC traction motors these days, as EMD uesd that technology in their locomotives in 1992. I would presume GE followed suit in their locomotives.
Maybe you, Mark, or Will might be able to basically explain it to me.
This is all I really know about it, thanks to a website I stumbled upon.
DYNAMIC BRAKING OPERATION
Dynamic braking is applied to the locomotive only. A dynamic brake interlock keeps the air brakes on the locomotive from being applied when automatic air braking and dynamic braking are being used.
APPLYING DYNAMIC BRAKING
Dynamic braking is applied in the following manner:
1. Move the Throttle handle to IDLE.
CAUTION: To prevent equipment damage when
changing from power to dynamic braking or from
dynamic braking to power, pause 10 seconds with
Throttle handle at IDLE and Dynamic Braking handle
OFF.
2. Move the Dynamic Brake handle to SET-UP position. Then move the handle into the BRAKING sector, as required.
3. After the slack is bunched, advance the Braking handle until the desired braking effort is obtained. Observe and correct braking effort during the initial period of dynamic brake application.
The amount of braking effort obtainable varies with the position of the Dynamic braking handle for various speeds. Maximum braking effort is obtained in the 8th Notch at speeds of about 49 mph.
NOTE: Wheelslip warning may occur while in dynamic braking. This indicates wheels are sliding. Sand is applied automatically to the wheels of sliding unit. Reduce the Braking handle position until the warning stops.
USE OF AIR BRAKES DURING DYNAMIC BRAKING
When necessary, the automatic air brake may be used in conjunction with the dynamic brake. Automatic air brakes will apply on the train but not on the locomotive. If the Automatic Air Brake handle is moved to the EMERGENCY position, the dynamic brake is removed and brakes on the locomotive, as well as those on the train, go into Emergency application.
CAUTION The independent air brake must not be
used during dynamic braking, to avoid flat spots on the
locomotive wheels caused by sliding.
RELEASE OF DYNAMIC BRAKING
Release dynamic braking by moving the Dynamic Braking handle to the OFF position.
Here is one that the engineer really screwed up big time......
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Railroad Accident Report
Derailment of Union Pacific Railroad Unit
Freight Tran 6205 West Near Kelso, California
January 12, 1997
NTSB Number RAR-98/01
NTIS Number PB98-916301
Synopsis: On January 12, 1997, about 11:52 a.m. Pacific standard time, the Union Pacific Railroad unit freight train 6205 west derailed 68 cars on the Union Pacific Railroad Los Angeles Subdivision, milepost 238.7, near Kelso, California. The train consisted of 3 locomotive units and 75 loaded covered hopper cars. While descending Cima Hill, the engineer inadvertently activated the multiple-unit engine shutdown switch, which shut down all the locomotive unit diesel engines and eliminated the train's dynamic braking capability. The train rapidly accelerated beyond the 20-mph authorized speed limit despite the engineer's efforts to increase the train's air braking, which the engineer placed in emergency 1 minute and 13 seconds after dynamic braking loss. The train's consist weight was listed at an average of 13 tons per car less than the train actually weighed. The train eventually reached a speed of 72 mph and derailed 68 of its 75 cars while exiting a siding near Kelso, California. No fatalities, injuries, fires, or hazardous materials releases resulted from the accident. The total damage cost was $4,079,152.
The National Transportation Safety Board determines that the probable cause of the derailment was (1) a prolonged pattern of inattention and lack of action by Union Pacific Railroad management to protect effectively or relocate the multiple-unit engine shutdown switch in SD60M locomotives after the switch had repeatedly been recognized as subject to inadvertent activation; and (2) failure of Union Pacific Railroad management to adequately address critical safety issues such as dynamic braking system operational reliance and protection, and authorized maximum train speeds in the event of dynamic braking failure. Contributing to the severity of the accident was the failure of Union Pacific Railroad management to ensure accurate car weight assessment and training for operating personnel on retainer-setting procedures and effects.
The major safety issues discussed in this report are the placement of safety-critical locomotive cab controls, adequate train-speed safety margins for steep-grade railroads, and the criticality of dynamic braking systems. The report also discusses accurate car weight reporting, the power brake rulemaking process, and the use of air brake retainers.
As a result of this accident investigation, the National Transportation Safety Board makes recommendations to the Federal Railroad Administration, the Association of American Railroads, and the Union Pacific Railroad.
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I wonder if the engineer was in the unemployment line after this one... 
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posted 02-03-2002 10:39 AM
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