DC Machines

The DC machines are of two types

• DC generators
• DC motors

A DC generator converts mechanical energy into electrical energy. And a DC motor converts the electrical energy into mechanical energy.

A prime mover supplies mechanical energy to the DC generator that generates electrical energy. From the DC source, the motor accepts the energy in the electric form and converts it into mechanical energy at its output (shaft).

To understand the operating principle of a DC motor, it is necessary to understand how does a current-carrying conductor experience a force, when kept in a magnetic field.

Windings in DC Machine

In any DC machine, there are two windings;

• Field winding
• Armature winding

Out of these, the field winding is a stationary winding and the armature winding is a movable (rotating) winding. The armature winding is mounted on a shaft. So, it can rotate freely.

The construction of a DC generator and DC motor is the same. It means we can use the same DC machine either as a generator or as a motor.

As shown in the above figure, a prime mover supplies mechanical energy to the DC generator and it generates electrical energy as an output. The output of the DC generator is supplied to the load.

The below figure shows the operating principle of a DC motor. It accepts the energy in the electric form from the DC source and converts it into mechanical energy at its output (shaft). The load is connected with the same shaft of the motor.

The field winding is connected across a DC power supply to operate the DC machine as a motor and armature winding also is connected across a DC power supply.

Due to DC field current flowing through the field winding, it acts as an electromagnet and produces flux in the air gap between the two windings.

The armature also carries a DC current. It acts as a current-carrying conductor placed in the magnetic field produced by the field winding. A mechanical load is applied to the shaft of the DC motor.

Principle of Operation of a DC Motor

The operating principle of a DC motor can be explained as follows:

When a current-carrying conductor is placed in a magnetic field, it experiences a force. The magnetic field is developed by the field current in the case of a DC motor.  i.e. the current flowing in the field winding.

The armature winding is connected to an external DC source. Hence, the armature winding is a winding that carrying current and placed in the magnetic field.

Due to the force exerted on it when placed in the magnetic field. it starts rotating and the armature starts rotating.

The direction of rotation depends on the direction of the magnetic field produced by the field winding as well as the direction of the magnetic field produced by the armature.