>If you ever measure or have seen the specifications for resistance through motors, armatures or their fields; there is very little resistance.

The higher the horsepower rating, the lower the resistance.

>An un-energized motor only has the normal resistance of the wire itself. If you were to hook a power source to it, it should be nothing more than a direct short.

For a 70 horsepower traction motor, the current at 600v with the armature blocked (not moving) is something on the order of 10,00 amps, which is very close to being a direct short.

>But once energized, the field and armature windings create magnetic fields which create a resistance to the flow of the electrons through the wire in the windings.

Once the impressed voltage and current establish stable magnetic fields in the field coils and armature (which occurs almost instanteously), no counter-EMF is generated unless the armature moves (rotates) because it's necessary for a conductor to cut lines of magnetic force before any electricity is generated (i.e. for the armature conductors to generate counter-EMF). And it's the counter-EMF which resists the current of the applied voltage as rotational speed increases (more lines of magnetic field cut per unit of time), not a change in the internal wiring's resistivity. This raises the effective resistance of the motor, but not its actual resistance (except for the temperature effect). At first glance, and to the casual reader, the difference between "effective resistance" and "actual resistance" sounds like splitting hairs, but it's not.

A magnetic field all by itself doesn't generate a current in a nearby conductor (a wire) unless it's changing in strength or the conductor is moving through the field (which causes it experience a change in the magnetic field's strength). This is called induction. It's how that transformer on the pole outside your house lowers the distribution voltage to 240/120, how the ignition coil in your car makes such high voltages to operate the spark plugs, and how commutator-less three-phase AC traction motors spin.

In a rotating, series-wound DC traction motor, the strength of magnetic field changes only with load (current). The armature coils generate because they experience a varying magnetic field as they move from field pole to field pole. It's the relative motion of the armature conductors and magnetic fields which causes the generation of counter-EMF because you could spin the field frame, keep the armature stationary, and get precisely the same results.

The interaction of the field coils' magnetic fields and the armature coils magnetic fields, both of which are caused by the impressed voltage, is what cause the motor to spin, enabled by that pole-changer called a commutator.

>As far as Mr. Lemp, he actually had two separate patents that are important to railroad gas/diesel-electric propulsion - First in 1914 was the load regulator that adjusts the electrical load to prevent overloading and underloading the prime mover. The second patent in 1924 was the exciter to balance the output of the main generator.

They (meaning Lemp and the company he worked for - GE) also developed a different configuration of main generator design because if you take one which is wound for constant-voltage, variable-current an put it in a diesel, which is variable-voltage and variable-current, heating and efficiency issues arise, causing problems. I forget the term for this design -- it's mentioned in On Time, but I haven't been able to find my copy of the book (re-organized my library last year, and some things are still hiding).

Note to our readers: we are discussing series-wound DC motors, not shunt nor compound wound ones.