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Re: Ed, that is my experience,with the physics of choo-choo's as well.
Author: Dr Zarkoff
Date: 01-24-2018 - 13:29
The are two considerations when reversing the motors: throwing the reverser and throwing the reverser and applying power. The second frequently causes more electrical damage.
For those of you who have access to When the Steam Railroads Electrified, take a look at the connection diagrams at the bottom of page 425. When all motors are connected in series (top line), simply throwing the reverser will do nothing. When they are connected in parallel pairs, second line, one motor will start generating before the other and try to drive it backwards (and that axle's wheels will be slipping). The connection shown by the bottom line, all motors in parallel, never occurs when the throttle is off. The thing to keep in mind is that in electric, diesel-electric locomotives, etc., the various connections are made by contactors. If the throttle is off, the contactors won't be making the connections, and nothing will happen. If the ground relay trips, the contactors will drop away and nothing will happen.
Every DC-drive electric locomotive which has three running points on its controller adheres to the progression sequence of these three connection schemes. Since the connections are made by it's control equipment in various controller positions other than off, nothing will happen if the reverser is thrown and the controller is off because less than line one applies, meaning there are no connections at all between motors. On the other hand, throwing the reverser in the controller and then opening the controller, even to just the very first notch, throws the motor reverser AND makes the connections shown by line one. Here is the difference between diesels and electrics: throwing the reverser in the controller on an electric does nothing to the motor reverser until you place the throttle in the first operating position. In a diesel, the act of merely throwing the controller reverser also changes the position of the motor reverser without having to open the throttle.
AC-drive electric locomotives use two types of traction motors: single phase and polyphase. Single phase traction motors are little more than DC motors with modifications for running on low-frequency AC (not much more than 25 hz -- locomotives like the P-5s and GG1s and the NH locomotives). Like with DC traction motors, the speed attained is related to the voltage and current of the impressed electricity.
Polyphase motors are a different animal in that a rotating magnetic field (in the motor frame) induces eddy currents in a rotor, and the magnetic fields of these eddy currents play a catch-up game with the external rotating field. The speed of the rotor is therefore dependent on the frequency of the impressed AC. Early attempts (100+ years ago) at polyphase AC motor speed regulation weren't all that practical nor efficient electrically, which is why the VGN and N&W squarehead locomotives had only two running speeds (on the GG1s, etc. all controller points were running points).
While the concepts and principles of speed regulation of polyphase motors via frequency control were figured out well over 100 years ago, they weren't practical for locomotive scale installations until the advent of solid state semi-conductors and microprocessor control in the early 1990s.
For those of you who have access to When the Steam Railroads Electrified, take a look at the connection diagrams at the bottom of page 425. When all motors are connected in series (top line), simply throwing the reverser will do nothing. When they are connected in parallel pairs, second line, one motor will start generating before the other and try to drive it backwards (and that axle's wheels will be slipping). The connection shown by the bottom line, all motors in parallel, never occurs when the throttle is off. The thing to keep in mind is that in electric, diesel-electric locomotives, etc., the various connections are made by contactors. If the throttle is off, the contactors won't be making the connections, and nothing will happen. If the ground relay trips, the contactors will drop away and nothing will happen.
Every DC-drive electric locomotive which has three running points on its controller adheres to the progression sequence of these three connection schemes. Since the connections are made by it's control equipment in various controller positions other than off, nothing will happen if the reverser is thrown and the controller is off because less than line one applies, meaning there are no connections at all between motors. On the other hand, throwing the reverser in the controller and then opening the controller, even to just the very first notch, throws the motor reverser AND makes the connections shown by line one. Here is the difference between diesels and electrics: throwing the reverser in the controller on an electric does nothing to the motor reverser until you place the throttle in the first operating position. In a diesel, the act of merely throwing the controller reverser also changes the position of the motor reverser without having to open the throttle.
AC-drive electric locomotives use two types of traction motors: single phase and polyphase. Single phase traction motors are little more than DC motors with modifications for running on low-frequency AC (not much more than 25 hz -- locomotives like the P-5s and GG1s and the NH locomotives). Like with DC traction motors, the speed attained is related to the voltage and current of the impressed electricity.
Polyphase motors are a different animal in that a rotating magnetic field (in the motor frame) induces eddy currents in a rotor, and the magnetic fields of these eddy currents play a catch-up game with the external rotating field. The speed of the rotor is therefore dependent on the frequency of the impressed AC. Early attempts (100+ years ago) at polyphase AC motor speed regulation weren't all that practical nor efficient electrically, which is why the VGN and N&W squarehead locomotives had only two running speeds (on the GG1s, etc. all controller points were running points).
While the concepts and principles of speed regulation of polyphase motors via frequency control were figured out well over 100 years ago, they weren't practical for locomotive scale installations until the advent of solid state semi-conductors and microprocessor control in the early 1990s.
