What is traction motor excitation, is it the same as "loading"?

What is "amplidyne" excitation, is it a generic term or a manufacturer term for a proprietary technology?

What other forms of excitation exist, which is better

In general terms, excitation is the current used in both a motor and a generator to create the magnetic field against which the driving current operates in a motor, or to control the amount of load that generator accepts. Only the smallest motors and generators use a permanent magnet, in the larger motors and generators, the stator is wound with wire and a DC current creates the magnetic field which the load reacts to, either for driving a motor or creating the current in a generator. The greater the DC current, the greater the magnetic field and the more load a generator will accept or the more power (torque) an electric motor will create. The advantage to varying the excitation current is that it allows the operator to vary the load without changing the speed (RPM) of the prime mover. In effect, this allows the generator/motor to appear to operate like an infinitely variable ratio transmission. It is also much more efficient than using a resistor bank which wastes the unused current as heat. Another advantage of controlling the motor or generator via excitation is that you can control very large motor or generators with very modest currents which means that much smaller switches and contactors can be used as opposed to the very large currents that are found on the prime mover necessitating large switches and heavy wire/cables.

Amplidyne, if my memory hasn't completely gone on me, is the use of an AC current generator that is rectified for use in the excitation coils. I'm not an electrical engineer, so I can't give you the specifics, but AC power is much easier to control than DC, so when you need fine voltage and current control, do it on the AC side and then rectify the AC to DC.

Ed

Is this how the Amtrak F 40's worked? I understand that they maintained a constant RPM for the HEP, but I never was sure how the speed control would have worked

'Amplidyne' is a type of exciter generator, i.e, a small DC generator designed to excite a larger DC generator. The most important characteristic of an amplidyne is the fact that it is a 'high-gain' exciter. In other words, a small change in the input will cause a large change in the output.

This device was used (along with something called a selsysn) for controlling the motion of WWII-era aircraft ball turrets. It may have been also used on surface ships to do the same thing.

"Amplidyne" was the moniker that GE assigned to the 'closed loop' generator excitation system that was applied to the post-war Alco road locomotive line powered by the 244 engine. The phrase 'closed loop' implies that the output of the system varies based upon changes in the input.

To be specfic, the Amplidyne system used saturable core reactors ( a form of transformer) that were constructed with a DC side and an AC side. The DC side of these devices measured traction current and voltage. On the AC side, there was a 400 Hertz AC signal supplied by a small motor generator set.

Are you with me ?

By design, there was a fixed amount of load current that could be generated in each throttle notch-minimum in notch 1 and maximum in notch 8. So, if the throttle was advanced to notch 8, the generator was able to develop full-rated load current. As a consequence, there would be changes in the AC output of the two saturable core reactors as the locomotive was taking up the load. The output of these reactors would be processed through a network of passive components (resistors, capacitors and rectifiers) and then applied to the field of the amplidyne exciter. In turn, the output of the Amplidyne is applied to the main generator field.

There were several advantages of this system. One is that it is extremely fast acting-based upon the fact that there were very few moving parts-all of which were small and could respond quicky to system changes. The other advantage is that the control signals and the traction current were electrically isolated from each other. This was an advantage to the maintainer. The disadvantage was the 'seeming complexity' of the system compared to the competitors' products.

Both EMD and WEMCO used a simpler 'open loop' type arrangement at the time Alco was using Amplidyne.

As for what is better-not an easy question to answer. Needless to say, the wholesale introudction of AC traction generators mandated the application of closed-loop controls by all the remaining builders.

That is where I ran into one, on board the USS Austin (LPD-4) built in 1963 (I think!). The ship used Amplidyne sets to translate the MK56 fire control system outputs into point and train orders for the four twin 3"/50 gun mounts. Each of the four twin gun mounts had it's own Amplidyne. The MK56 F/C system was removed in 1977 as well as two of the twin 3"/50 mounts. The remaining two mounts were controlled by "Kentucky Windage" there after. With a good gunner, the 3"/50 was very effective out to about 10K to 12K yards. But the gun was maintenance intensive and ate spare parts on a regular bases. They were completely removed from the Atlantic fleet by about 1985 and they were gone from the Pacific fleet by 1990. I believe the same Amplidyne set up was use on the "Garcia" Class Frigates. They had a MK56 F/C system controlling two single mount 5"/38 guns. The MK56 system was developed late in WWII as an "angle rate" F/C system, mainly intended to provide better performance for close in closing a/c targets. Ships built up to the late 1960's often had an interesting mix of modern and WWII era equipment. The Austin had an internal telephone PBX pulse dial switch that was originally built for the USS Boxer. It was replaced with a modern digital switch in the same overhaul that the F/C system was removed.

Ed