Field Weakeening (Shunting) and transition

[plainsman]

KUJU technical group:
The article on field weakening seems to bring some interesting questions. One point that I am misunderstanding, Does KUJU mean that in KRS there will be a limit of 5 stages of field weakening (shunting is the term used over here)? The reason I ask, is the EMD GP35 had 9 stages prior to transition, and 5 stages following transition. I think this is the most complex unit I am aware of in North American operation. Will KRS allow this unit to be modeled accurately? Also will you be able to define series and parallel configurations in transition? The typical variations are S, SP, 2S-3P, 3S-2P, and P.
I posted this in the British forum, but that thread seems to be sidetracked with some off topic personal distraction. Please excuse if you see the question in both forums!
BTW, does this mean that AC locomotives will be able to be accurately modeled with 3 phase frequency controlled traction motors, with proper dynamic braking and correct power calculation model? I have the correct AC equations if you need the math?
Bob Boudoin

[kujuSabrina]

>KUJU technical group:
>The article on field weakening seems to bring some interesting
>questions. One point that I am misunderstanding, Does KUJU
>mean that in KRS there will be a limit of 5 stages of field
>weakening (shunting is the term used over here)? The reason I
>ask, is the EMD GP35 had 9 stages prior to transition, and 5
>stages following transition. I think this is the most complex
>unit I am aware of in North American operation. Will KRS allow
>this unit to be modeled accurately? Also will you be able to
>define series and parallel configurations in transition? The
>typical variations are S, SP, 2S-3P, 3S-2P, and P.
>I posted this in the British forum, but that thread seems to
>be sidetracked with some off topic personal distraction.
>Please excuse if you see the question in both forums!
>BTW, does this mean that AC locomotives will be able to be
>accurately modeled with 3 phase frequency controlled traction
>motors, with proper dynamic braking and correct power
>calculation model? I have the correct AC equations if you need
>the math?
>Bob Boudoin



Hi Bob,
Rail Simulator can deal with any number of field diverts, and dynamic braking is supported.

[plainsman]

Hi Sabrina,
Thanks for the reply!
That is good news with unlimited field diverts.
I had no doubt that the simulator would model dynamic braking, but my question related to the dynamic braking and special traction situation associated with 3 phase AC locomotives. Because of the 3 phase nature of AC traction motors in RRing, for the same voltage and amperage and efficiency, a 3 phase AC traction motor will do ~1.73 more work compared to a DC traction motor with the same voltage and amperage and efficiency. Therefore for AC locomotives:
Horsepower= (volts x amps x efficiency x power factor x 1.73)/746
for DC:
Horsepower= (volts x amps x efficiency)/746
An SD70M-2, the highest efficiency DC design now available, can only reach about between 89.5-90% transmission efficiency (in other words, of the 4,300 HP output of the prime mover (diesel engine), only about 3860 HP is available at the rail to do work.
The AC counterpart, the SD70ACe, has about a 93.6% transmission efficiency. This means it has 4025 HP available at the rail. The power factor is a function of how accurately the onboard computer can maintain full frequency synchronization. For the GE GEVO units this approaches a power factor of 98.4%. and an SD70ACe would be 97.5-98% Even the early SD70 and AC4400 AC locomotives would have power factors of ~97%.
Thus for any given electrical input:
A SD70ACe will be able to do work at a ratio of 9.128:5.173 to an SD70M-2, or 1.765 times the work of an SD70M-2.
Now as to dynamic braking, AC traction motors allow a locomotive to have dynamic braking ability down to very slow speeds (as low as 0.4 mph), and to have a much steeper rise in total dynamic braking force from that very slow speed to peak retarding force.
Now as to adhesion, The SD70ACe has maximum adhesion of about 46.8% and the GE AC GEVO units maximum adhesion of about 47.2%. This compares to their DC counterparts with about 37% maximum adhesion. The ~10% adhesion advantage enjoyed by the AC locomotives, is due to the precision with which frequency control can maintain smooth power flow to the AC traction motors as compared to the less smooth power input for the DC counterparts.
I would be happy to discuss tthis in greater depth if someone would like?
Hope this helps,
Bob Boudoin