Type of DC Motor, shunt, series and compound motor ~ Electrical & Electronics Knowledge

Type of DC Motor

Direct current motors are named according to the connection of the field winding with the armature. There are three types of DC motor.

1. Shunt wound or shund motor.

2. Series wound or series motor.

3. Compound wound or compound motor.

Shund motor:

This is the most common type of dc motor. The field winding is connected in parallel with the armature, as shown in fig below

DC. Shunt motor

The current, voltage and Power equations for a shunt motor are written as follows :

Current equation

By KCL at junction. Sum of the incoming currents at junction = sum of the outgoing current at junction.
I = Ia + Ish

Where I = input line current
Ia = armature current
Ish = shunt field current

Voltage equation :

The voltage equation are written by using Kirchhoff's voltage law (KVL).

For field winding circuit

V = Ish × Rsh

For armature winding circuit

V = E + Ia Ra

Power equations :

Power input = mechanical power developed + losses in the armature + loss in the field

VI = Pm+ I²a Ra + I²sh Rsh

= Pm+ I²a Ra + VIsh

Pm = VI - VIsh - I²a Ra

= V( I - Ish ) - I²a Ra

= VIa - I²a Ra

Pm = EIa

Multiplying equation ( V = E + Ia Ra ) by Ia we get,

VIa = EIa + I²a Ra

VIa = Pm + I²a Ra

Where,

VIa = electrical power supplied to the armature of the motor.

Series motor :

In the series motor the field winding is connected in series with the armature. As shown in fig below.

Series motor

Current equation :

By KCL in fig

I = Ise = Ia

Where Ise = series field current

Voltage equation :

By KVL in fig

V = E + I (Ra + Rse)

Power equations :

Multiplying equation{ V= E + I (Ra + Rse)} by I we get

VI = EI + I²(Ra + Rse)

Power input = mechanical power developed + losses in the armature + losses in the field

VI = Pm + I²a Ra + I²Rse

Comparison of equations VI = EI + I²(Ra + Rse) and VI = Pm + I²a Ra + I²Rse shows that

Pm = EI

Compound motor :

A DC motor having both shunt and series field winding is called a compound motor. It may be a short-shunt compound motor or a long-shund compound motor.

Compound motor

A DC compound motor may be cumulative compounded or differentially compounded . The current relationships for a compound motor can be written by using KCL. The voltage relationships are written by using KVL.

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