Forums

[spikejones52002]

What are the advantages of A.C. Traction Motors  over D.C. and visa versa?

[CAZEPHYR]

What are the advantages of A.C. Traction Motors  over D.C. and visa versa?

 

Prototype AC Traction Motors can lug at much slower speeds without burning up like a DC Traction motor.   They have higher levels of dynamic braking and can hold trains on a hill if required by the dynamics.  The disadvantage of the AC unit is the cost of the AC package.   The increase in cost seems to be worth the price for heavy coal train use.  The DC advantage is lower cost.

When the AC units first came out, DC locomotives that were used with AC motors in the lead could be damaged or burned up and operating rules had to be followed to prevent problems.  I have noticed that this practice is not the norm any longer as the Union Pacific uses AC's in the lead and DC units in the consist fairly often, which limits the use of the lead AC unit.  The AC unit cannot be allowed to lug slowly for any long period or the DC units will be damaged.   

You find and read articles about AC versus DC in past Trains Magazine articles. 

Hope this helps.

 

In HO scale, I find there is very little difference.

[BNIRRLives]

 

DC is alot easier on a Electricians

[spikejones52002]

I can not see how the cost of controlling a motor could be a factor.

All controls systems cost.

When a train is up to speed, Is there any factors for choosing one or the other?

[tomikawaTT]

I can not see how the cost of controlling a motor could be a factor.

All controls systems cost.

The AC fed to the traction motors of an AC locomotive is not the plain-jane sine wave AC found in your wall sockets.  It's more like the output of a model railroad DCC decoder.  To complicate the matter, each traction motor has to have its own controller - a complex electronic gadget that has to combine high current capacity with extremely precise control of the output waveform.

When a train is up to speed, Is there any factors for choosing one or the other?

The place that AC shines is in VERY low speed hauling.  DC traction motors heat up and must have their input power reduced.  AC traction motors are far more efficient and don't generate massive amounts of excess heat.

Chuck

[Trainmaster.Curt]

When it comes to AC Traction, i think the CPR's newer locomotives are mostly AC4400CW's and ES44AC's, i could be wrong, well unless their older engines are DC's.

[Gary UK]

The DC motor also has a commutator whereas the AC motor is brushless. Because of this the DC motor is more sensitive to dirt and water ingress/build up and the associated damage caused by flashover's. High speed running combined with carbon brush dust build up can also do it.

Ive seen a few DC traction motors that have spewed most of the brush gear and commutator around the inside of the casing after flashover. It can aslo take the generator with it "in sympathy" as its known.

[spikejones52002]

D.C. motors are individually controlled for slippage.

A.C. seems to be so much better.

I wonder why a railroad would want new D.C. traction any more.

I know the Alaska RR has GP/SD70 macACs.

[Anonymous]

D.C. motors are individually controlled for slippage.

A.C. seems to be so much better.

I wonder why a railroad would want new D.C. traction any more.

I know the Alaska RR has GP/SD70 macACs.

First off, there is no such thing as a GP70, last production GP model was the GP60 family. Second I'm not sure what you're getting at in your post. You state why would a railroad still buy DC units then give an AC unit (SD70MAC) as an example. Something doesn't add up.....

The reason the Alaska RR is buying MACs and not ACes is because MACs are cheaper and since the ARR isn't a class one they don't have to obey the Teir II emission standards the class ones are bound by.

[carnej1]

 IIRC the "Tiered" emissions requirements apply to much more than just the Class 1 railroads. If smaller railroads were exempt wouldn't FEC and MRL have ordered non-compliant 70 series models and saved a few bucks? I know for a fact that both truck and heavy equipment diesel engines are having to meet similiar standards. I was under the impression that the ARR units were the last non "E" model SD70's to be built for North America. In other words if there is a follow on order they will be ACEs.

 I have read that one of the reasons that ARR went with the AC model was the ability to modify them to provide head end power to passenger cars by switching one of the three AC converters from supplying traction current to supplying HEP. This means that when operating in passenger mode the units actually run as A-1-A rather than C-C (by flipping a switch they revert to 6 motors for freight service). I think that only the second order of Alaska SD70MACs have this option....