Types of DC Motor

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Types of DC Motor

The main function of dc motor is convert electrical energy into mechanical energy.
There are two main parts of dc motors is stator and rotor which has field winding and armature winding respectively.

According to the connection of field winding with the armature winding , dc motor has following types

  1. Separately Excited DC Motor
  2. Shunt wound motor
  3. Series wound motor
  4. Compound wound motor

Separately Excited DC Motor:-

saperately excited dc motor

In a separately excited machine the field winding is independent of the armature winding. separately excited DC motor the supply is given separately to the field and armature windings.The armature and field winding voltage loop equations are,

   Ia  = IL             AND         Eb = V – IaR+ brush drop

At lower current levels, the flux-current relationship is linear, but as the current increases, the iron in the machine starts to saturate. The field current (and hence flux) can be controlled by either adjusting the field circuit resistance or the field supply voltage. For a separately excited machine, the armature current equals the armature terminal current.

Shunt wound motor :-

shunt field dc motor

Fig shows the connection of shunt wound dc motor.
In shunt wound dc motor the field winding is connected in parallel with the armature winding. both winding are in parallel to each other. Hence the voltage across both winding is same as the applied voltage. shunt field winding resistance is very high. Therefore, shunt field coil consists of many turns of thin wires. Shunt field is connected across the constant supply voltage. Hence, the field current Ish remains constant. Ish is proportional to the flux  so flux remain constant.

IL= line current
Ia=Armature current
Ish= shunt field current
Rsh = shunt field resistance
Ish = V/Rsh
IL = Ia + Ish
Eb = V – IaRa  
Motor input VIL

Series wound motor:-

series field dc motor

Dc machine with a series connected field winding is shown in fig. To indicate that the field winding is connected in series with the armature winding. series field winding has low resistance and it is consist of less turn of thick wires.The entire armature current flows through the field winding as its connected in series to the armature winding. hence, the armature current is equal to the filed current.

IL= line current
Ia=Armature current
Ise= series field current
Rse = series field resistance
Ra= armature resistance
IL= Ia = Ise 
Eb = V – Ia(Rse+Ra)
Motor input VIL

Compound wound motor:-

long and short shunt dc motor

when DC motor consist both shunt and series field winding then its called compound wound motor.they both windings wound on each pole. flux is provide by both.compound wound motor has divided in two parts,
1. Long shunt compound:- when shunt field winding is connected across the both series and armature winding, its called long shunt compound motor.
Ise  = Ia
IL = Ise + Ish
Eb = v – IaRa – IseRse

2. Short shunt compound:- when shunt field is connected across only the armature winding , its called short shunt compound.
IL = Ise
Ia = Ish + IL
Eb = v – IaRa – IseRse

The main advantages to used this type motor is that, shunt field winding gives the constant speed. series field winding gives the high starting torque when motor is started under heavy load.

 

If any query or suggestion about DC Motor please comment below or Email on sohal@electricalidea.com.

 

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