Types of DC Motor:  In this section, we will give an insight into the types of dc motors. The topics under discussion are dc shunt motor, dc series motor, and compound motor. While discussing types of dc motors we will be giving an insight into the equivalent circuit and voltage-current relationship of the motors.

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## DC Shunt Motor

A DC Shunt motor is a type of dc motor where the field winding is connected in parallel with the armature winding. Finally, a dc supply is applied across such motors. The figure below shows a dc shunt motor.

Fig: DC Shunt Motor

Here, Rsh is the shunt field winding resistance and Ra is the armature winding resistance. The resistance of shunt field winding is large compared to the armature winding resistance. The winding of the shunt field has a greater number of turns and less cross-sectional area.

### Voltage and Current Relationship

In these types of dc motor, the supply voltage is in parallel to Ra and Rsh so the same voltage appears to cross armature winding and shunt field winding.

Where Eb is the back emf of the dc motor and Vbrush is the voltage drop in the carbon brush of the motor. The Vbrush is generally neglected.

In these types of dc motor, the flux produced by the field winding is directly proportional to the current through it i.e. Φ ∝ Ish. Hence, as long as the supply to the motor is constant, the flux is constant due to which the dc shunt motor is also called the constant flux motor.

### DC Series Motor

In a dc series motor, field winding and armature winding are connected in series. The figure below shows a dc series motor.

Fig: DC Series Motor

Here, Rse is the series field winding resistance and Ra is the armature winding resistance. In these types of dc motor fields winding resistance is very small with small numbers of turns and a large cross-sectional area.

### Voltage and Current Relationship

Let IL be the current drawn from the supply then, in the case of dc series motor.

In this case, if dc series motor, the flux produced is directly proportional to the current flowing through the armature as the entire armature current flows through series field winding.

i.e. Φ ∝ Ise Ia ∝ IL

### DC Compound Motor

DC compound motor is further divided into a long shunt compound motor and a short shunt compound motor. In these types of dc motor, part of the field winding is connected in series with the armature, and part of the field winding is connected in parallel with the armature.

### Long Shunt Compound Motor

In a long shunt compound motor, the shunt field winding is connected across a series combination of armature and series field windings.

Fig: Long Shunt Compound Motor

Here, Rse and Rsh are series and shunt field winding resistance respectively. If IL is the total current supplied by the dc source.

### Short Shunt Compound Motor

In these types of dc compound motor, the shunt field winding is connected in parallel with armature winding, and this combination is connected in series with the series field winding and dc source. The figure below shows a short shunt compound motor.

Fig: Short Shunt Compound Motor

If IL be the total current supplied by the source,

Also, the dc motor types can be further classified as cumulatively compound motors and differential compound motors. If the fluxes produced by the two field windings aid each other then these types of dc motors are termed cumulatively compound motors.

If the fluxes produced by the two field windings cancel or oppose each other then these types of dc motors are termed differential compound motors.

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