A DC compound motor is a type of direct current (DC) motor that combines characteristics of both series-wound and shunt-wound DC motors. It contains both series and shunt field windings, allowing it to exhibit a mix of speed and torque characteristics from both types of motors. Compound motors are commonly used in applications requiring high starting torque and relatively constant speed over a wide range of loads. There are two main types of DC compound motors based on the connection of the field windings:

1. Cumulative Compound Motor:

   • In a cumulative compound motor, the series field winding is connected in series with the armature winding, while the shunt field winding is connected in parallel with the armature winding.
   • The series field winding adds to the magnetic field strength produced by the shunt field winding, resulting in a motor with high starting torque characteristics similar to a series motor.
   • As the load increases, the armature current and the magnetic field strength produced by the series field winding also increase, leading to a relatively constant speed characteristic.

2. Differential Compound Motor:

   • In a differential compound motor, the series field winding is connected in series with the armature winding, while the shunt field winding is connected in opposition (opposite polarity) with the armature winding.
   • The series field winding opposes the magnetic field produced by the shunt field winding, reducing the overall magnetic field strength and resulting in a motor with a more stable speed characteristic.
   • Differential compound motors are less common than cumulative compound motors and are used in applications where speed regulation is critical, such as in machine tools and industrial drives.

Both types of compound motors offer advantages and disadvantages depending on the application requirements. Cumulative compound motors provide high starting torque and are suitable for applications with heavy starting loads, while differential compound motors offer better speed regulation and are suitable for applications requiring precise speed control. The choice between the two types of compound motors depends on factors such as load characteristics, speed requirements, and torque demands of the application.