Finally have a chance to read throught some of the online locomotive manuals out there. Started first with the EMD GP7 manual from 1951. I'm afraid I may have a few questions as I go. If this is a good forum to ask in, I would be grateful for some info from those with experience.
I read through the section about the transition forestalling switch and can see that it is used to "forestall an undesired forward transition." In other words is that a jerky start? and how, mechanically and electrically is this accomplished with the switch and its effect on the traction motors?
Thanks.
9. What is shunting? As the speed of a locomotive increases, the traction motors generate large amounts of extra electricity that is simply not needed. This creates resistance in the motors (called counter-emf) and reduces the amount of amperage going into the motors, which limits speed. Shunting is a process in which the resistance is reduced by lowering the flow of electricity to the magnets that create the EM field in the motors without reducing the amperage. This lowers the resistance the traction motors face. (Think of shunting as like shifting gears in a car)
20. What is transition? A procedure that reduces the resistance the traction motors (see shunting) face by changing the proportion of amperage and voltage while not changing the output of the alternator. This reduces counter-emf. This allows the locomotive to develop more amperage and volts as needed. Transition may cause a brief interruption in tractive effort and can result in a broken coupler if slack develops and then the cars snap back as TE resumes. (Think of transition as like shifting gears in a car)
grizlump
I can't even spell it and you expect me to know what it is.
Here's a WAG: it locks up the traction motors so they don't cut out -- transition -- in an overload condition. This would primarily be used on a grade so that the train doesn't stall because an overload condition develops in the (diesel) locomotives on the point.
From the far, far reaches of the wild, wild west I am: rtpoteet
didn't some of the early diesels, like emd covered wagons, have manual transition? the control looked like a little reverser lever.
grizlump (grumpy german)
Thanks for the reply. Yes, it seems some of the early locos had manual trasition, at least that much is implied in the section from the GP7 manual below when referring to the transition lever . And manual transitioning seems in order when the loco had dynamic brakes......if I am reading this right.
106 Transition Lever The basic GP7L locomotive is not equipped with a transition lever. There are, however, certain types of the GP7 that are equipped with transition levers, even though transition (forward and backward) is fully automatic on the GP7 locomotive. The inclusion of such a lever is principally for use with dynamic brakes, or for the purpose of providing a means for effecting manual transition in other type units (not equipped with automatic transition) when such a unit is being used in multiple unit operation with a GP7. Thus, the transition lever has 5 positions: OFF, 1, 2, 3 and 4; if the locomotive is equipped with dynamic brakes, an additional position "B " (braking range) is also included.
Earlier production GP7 locomotives that were equipped with transition levers had this lever arranged to control the Road-Service feature. On those locomotives, the placing of the transition lever in the OFF position caused the locomotive to start with the "teaser" type of starting; placing the transition lever in the #1 position caused modified maximum field starting to be obtained. Present production locomotives, however, have a toggle switch (located on the side of the controller) to control the Road-Service feature, see Art. 108. Thus, the controller on the GP7 has mechanical interlocking of the levers identical to that found on "F" type locomotives, see Art. 109.
107 Transition Forestalling Switch This switch is located on the engineman's control panel and is used to forestall an undesired forward transition.
When the switch is in the "UP-AUTO" position, forward transition will take place automatically at the proper time.
When forward transition is not desired, the switch is placed in the "DOWN-SERIES" position. Traction motor connections will then stay in series load parallel, regardless of locomotive speed, generator voltage or position of regulator arm, Fig. 1-6.
The transition forestalling switch should not be moved from the "SERIES" to the "AUTO" position unless the throttle is in the 6th position, or lower. However, if the speed of the locomotive is below the forward transition speed, it is permissible to move the switch to the "AUTO" position with full throttle operation. This will prevent any possibility of forward transition taking place at an excessively high voltage.
Movement of the switch from the "AUTO" to the "SERIES" position may be done at any time, as this will not cause backward transition to take place. Backward transition is determined only by the operation of the backward transition relay, or by reducing the throttle to the "Idle " position.
The operation of the transition forestalling switch is not trainlined. In multiple unit operation, the forestalling switch in each unit must be placed in the position in which it is desired to operate the locomotive.
My next and related question is about the series-parallel and variation of that connection that the engineer had option to select.
To answer about the transition switch. Southern Pacific commute locomotives had this switch. When set to "COM" or PASS, the locomotive would not make transition, thus permitting much better acceleration in stop and go service. When placed into the FRT position, the locomotive would act like a normal freight locomotive, making transition. SP's SW1500's also had a type of switch similar to this, to assist in making jackrabbit starts in kicking and dropping cars. Flipping the switch raised engine rpm and allowed a smooth start to the "kick". Once moving, flipping the switch over caused the locomotive to take off like a scalded dog, permitting quick action in kicking or dropping of cars.
If I remember, the locomotive went from series to parallel in automatic transition, and the engine produced a "bump-and-surge" effect as the transition was made. Amtrak engines today do not make transition, to my knowledge, and do not give the famous "bump-and-surge" that freight locomotives do.
As a matter of fact, a student engineer I had got a freight unit on a passenger train recently and the freight unit made transition upon acceleration. Scared the heck out of him; he thought the engine was going to fly apart, or that it was malfunctioning. With no freight experience, he did not understand transition, how it feels and what to look for on a freight unit. The unit was only acting normally.
Our MP15ACs have a 4 position switch.
Normal - Self-explanatory
Series/Forestalling - This keeps other older engines from making transition at low speeds. The MP15AC runs normally, as it doesn't make transition.
Switch 1 - Gives more amps when throttle is opened.
Switch 2 - Revs the engine up when the reverser is not in center. Also gives more amps.
I think EMD 4-axle units with AC main gens don't make transition, they just keep pulling. Our MP15ACs and GP38ACs don't. SD50 and newer may not make transition either, something about generator transition.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com