Which three types of direct-current motors are fundamental?

The three fundamental types of direct-current motors are series, shunt, and compound motors, making this the correct answer. Each type has distinct characteristics based on how the field windings are connected in relation to the armature circuit.

• Series motors have their field windings connected in series with the armature, which means that the current flowing through the armature also flows through the field winding. This configuration allows series motors to produce very high torque at low speeds, making them suitable for applications requiring high starting torque.

• Shunt motors have their field windings connected in parallel (or shunt) with the armature. This arrangement allows the field strength to remain more constant regardless of variations in armature current, resulting in more consistent speed under different load conditions. Shunt motors are commonly used in applications where stable speed control is essential.

• Compound motors combine features of both series and shunt motors. They have both series and shunt windings, allowing them to benefit from the high torque capabilities of series motors while maintaining speed stability like shunt motors. This versatility makes compound motors suitable for a variety of applications, including those requiring heavy starting loads and stable operation.

The other options provided include incorrect configurations or types of motors not classified as fundamental direct