EMD and GE make a big deal about how AC has made DC obsolete, yet railroads continue to purchase Dc locomotives by the droves. What true advantages do AC locomotives have? What are their disadvantages(other than cost)? Why are certain types of locomotives ideal for certain types of trains(coal, frieght, intermodal, ect.)
I think that AC have no advanage other then the RR like to use them for moving coal and other heavy material. RR use DC for intermodal, and manisets more often then not.
OK, yes DC’s are cheaper, but are at a big disadvantage to AC’s.
Advantage, is that AC motors do not burn up like the DC’s can. The reason for that is because the AC motors are brushless and require less maintanace.
One the question of if they are run on certain things, yes and no. AC’s are really liked be used on coal trains and heavy manifests. But on the UP, what it has on hand, is what they use. I have seen 5 AC’s on an intermodel, and I’ve seen 4 DC’s on a coal. So it really don’t matter what type of units are put on the lead, as long as it gets there. I know there are several other things that I am missing so I’ll let others do it.
Later, Dru
The simplified technical explanation.
In the best of all possible worlds:
AC traction motors over far superior low speed service and also are superior in low speed dynamic breaking mode. Thus many roads prefer them for moving heavy,low speed trains(coal) and for service in mountainous territory (CSX AC60CW’s on the Boston line).Dru also correctly mentioned that AC motors are lower maintenance.
DC traction locomotives are cheaper to purchase and in high speed service,offer performance comparable to AC engines. Thus UP’s huge leasing of SD70M’s for manifest and intermodal service,and BNSF, who for have split EMD orders between SD70MAC’s for bulk service and SD75M’s for fast freight.