🔍 Key Concepts

• Difference between AC (alternating current) and DC (direct current) motors in terms of brushes/commutators • Which parts of a diesel‑electric system are electrical rotating machines versus static components • Typical sources of wear and tear in electrical machines (moving contacts vs. no moving contacts)

💭 Think About

• Think about which of the four options physically changes when you go from a DC propulsion system to an AC propulsion system. • Ask yourself: which component in a DC system usually has brushes and a commutator, and what is the AC equivalent of that component? • Consider which items on the list are mostly mechanical (same either way) and which are electrical machines that might be designed differently in AC versus DC.

✅ Before You Answer

• Identify which listed components are the same in both AC and DC diesel‑electric systems (these likely have similar maintenance needs). • Recall that DC machines usually have brushes and commutators; AC machines typically do not—which choice corresponds to that change? • Verify which component’s design change from DC to AC would most directly reduce routine mechanical wear maintenance, such as brush replacement and commutator cleaning.