What is the minimum number of field windings required in a compound motor?

A compound motor combines two types of windings: series and shunt (or parallel) windings. The essential function of these windings is to enhance the motor's performance by providing different characteristics based on their configurations.

The series winding is responsible for producing high starting torque, as the current flowing through it is the same as that flowing to the armature. On the other hand, the shunt winding is connected to the supply voltage and helps regulate the motor speed and maintain the torque under variable load conditions.

Since a compound motor requires both a series and a shunt winding, the minimum number of field windings necessary to constitute a compound motor is indeed two. This setup allows the motor to function effectively across a range of operating conditions, balancing between the high torque needed at startup and the speed control afforded by the shunt winding.

The other options don't provide the necessary variety of windings to fulfill the compound motor's design, as at least two distinct windings must be present to achieve the intended functionality.