This idea that you need a larger transformer when you simply add more track is incorrect.
You need a transformer with a higher amperage rating when you start drawing more power — such as when you add accessories, lighted cars or a more powerful locomotive.
When you add track, you tend to lose voltage, due to resistance at rail joints and from the metal itself. The solution is to add feeder wires to the more distant sections.
Obviously, something else is causing the locomotive to drawing more amperage, in this particular case.
