🔍 Key Concepts

• Construction differences between wound-rotor and squirrel-cage induction motors • How rotor current is accessed or controlled in a wound-rotor motor • Typical uses of slip rings, commutators, and centrifugal switches in AC and DC machines

💭 Think About

• Think about which component allows external resistance or control to be added to the rotor circuit of a three-phase induction motor. • Ask yourself: which of these devices is normally associated with DC machines versus AC induction machines? • Consider which item is used to open the starting winding on a single-phase motor, and eliminate that from a three-phase context.

✅ Before You Answer

• Identify which item is specifically used to connect the rotor winding of an induction motor to external circuits (starting resistors, speed control, etc.). • Eliminate any components that are primarily associated with DC motors or single-phase split-phase motors rather than three-phase induction motors. • Confirm that the remaining component is located on the rotor shaft and makes contact with stationary brushes.