AC vs DC power on Z-Trains.

[Anonymous]

I have noticed alot of UP trains running esply Intermodel's running alot of mixed AC&DC power.....WHY?
If AC is much slower than the DC counter part than why do they put them(AC)'s on Z-Trains?
Is there ANY Railroader who can explain this?

[Anonymous]

AC units aren't slower, slow drag type service is just where the advantage of AC traction diesels is. Nothing prevents them from being used in high speed service.

[GP40-2]

CSX uses a lot of AC power on high speed trains also. Not suprising, since they only buy AC power now[:D]

Like xBNSFer said, ACs aren't just for slow speed service. It is just that AC traction has avantages over DC motors in high power slow speed service. AC induction motors also have advantages over DC in high speed operation. AC induction motors can operate at higher rpm and are electrically more efficient than DC motors. For example, CSX's AC4400s can produce 180,000 lbs continious tractive effort at slow speed, but also easily operate at 75 mph.

The one downside is AC locomotives are more expensive than DC at the present time. However, EMD has been making claims than they will be able to produce the new SD70ACe at a similar cost of the DC version.

I read that AC induction motors now have 98% of the world market for heavy industrial motors (i.e. heavy duty motors used in manufacturing, etc)

[Anonymous]

Wow ,I guess that changed my mind then.

[dehusman]

Also UP has some 6000hp AC locomotives. Z trains love HP.

Dave H.

[Anonymous]

I've also noticed that BNSF around Chicago seems to be mixing AC & DC together a lot more lately. In the past coal trains would usually get 2 SD70macs, slower intermodals would get 2 Dash-9s or 2 SD40-2s, and the Z-trains would have 3 or 4 Dash-9s. Lately it seems like almost any combination may be seen on any type of train. It might be related to grain, I'm starting to see a lot more grain trains, often drawing the SD40-2s.