Which of the following is NOT a type of armature winding?

The correct answer is that spiral winding is not recognized as a standard type of armature winding used in electrical machines. In the context of armature windings for motors and generators, the other options—lap winding, wave winding, and frog leg winding—are well-established techniques used to configure coils on the armature.

Lap winding is characterized by its overlapping coils that connect in a way to minimize the total number of turns while maximizing the current-carrying capacity. This design allows for a more efficient torque generation in motors.

Wave winding, on the other hand, features coils arranged in a manner that creates a wave-like shape, typically yielding smoother operation and better magnetic field interactions.

Frog leg winding is a less common but still valid configuration that involves creating coils that resemble the shape of a frog's legs. This winding style is often utilized for specific applications that benefit from its unique characteristics.

In summary, while lap, wave, and frog leg windings are established types used frequently in electrical engineering, spiral winding does not fit within this recognized set and thus, is the correct answer to the question.