DC Compound Motor : Definition,Types and characteristics - Electrical Diary

DC Compound Motor 

DC Compound motor are special types of motor in which two types of  field winding is available.Its one field winding is connected in series and other is connected across the armature.Due to both type of winding in DC Compound motor its characteristics is intermediate of DC series motor and DC Shunt Motor.DC Compound Motor are classified into two categories 

• Cumulative Compound Motor
• Differential Compound Motor

Cumulative Compound Motor

if the magnetic flux produced by the series winding assists the magnetic flux produced by shunt then is called Cumulative compound motor.Cumulative compound motor also classified into two categories

• Long shunt type
• Short Shunt type

Long Shunt Compound DC Motor

When the shunt field winding is connected parallel to both armature and series winding then this motor is called long shunt compound motor.Circuit diagram of long shunt compound dc motor is given below.

Short Shunt Compound DC Motor

When the shunt field winding is connected parallel to armature winding only then this motor is called short shunt compound dc motor.The circuit diagram of short shunt compound dc motor is given below.

Characteristics of Cumulative Compound DC Motor

Characteristics of Cumulative dc motor is given by curve.This curve is draw between two different parameter of compound dc motor.

Torque Load Characteristic

Torque load characteristics of cumulative compound dc motor is given below.

From this figure it is very clear that torque developed in cumulative compound dc motor is less than the shunt motor at full load but is greater than the series motor.the starting torque of cumulative dc motor is greater than the starting torque of shunt motor.from figure it is also clear that as load current increases, the torque also increases.

Speed torque characteristics 

Speed torque characteristics of cumulative compound dc motor is given below by a curve between speed and torque.

From the given curve it is very clear that at low torque the speed of the motor is very high but as the torque increase the speed of motor decreases slowly.it means that this motor is capable to bear high load but not able to bear sudden over load.

Speed torque characteristics

Speed torque characteristics of cumulative Compound DC motor is given below by a curve between speed and torque.

From give figure it is shown that the speed of the motor reduces as the load current increases.But the speed variation of this motor is intermediate of series and shunt dc motor.

Differential Compound DC Motor

A compound dc motor in which the series winding so connected that it will oppose the field flux of shunt field winding the this type of dc motor is called differential compound dc motor.Differential compound dc motor are also classified into two type i.e (a) Long Shunt type (b)Short Shunt Type
During the starting of differential compound dc motor the series winding is short circuit due to this this motor start as shunt motor with a constant speed .

Long Shunt Type

In this type of DC motor the shunt field winding is connected across the armature and series field winding.The series field winding is connected in series with armature winding so that it will produce magnetic field which oppose the field flux of shunt.the circuit diagram of long shunt differential motor is given below.

Short Shunt Type

In this type of DC motor the shunt field winding is connected across the armature winding.The series field winding so that it will produce magnetic field which oppose the field flux of shunt.the circuit diagram of long shunt differential motor is given below.

Characteristics of Differential Compound DC Motor

Different different characteristics of differential compound dc motor is given below by curve between two different parameter of motor.

Torque load Characteristics

The torque load characteristics of differential compound dc motor is given below between torque and load curve.from the given curve it is clear that when load current increase,the torque also increases for a given value of load current,beyond the value of this load current torque is almost constant irrespective of the load current.

Speed Torque Characteristics

Speed torque characteristics of differential compound dc motor is given below by a cure between speed and torque.from the curve it is clear that speed of the motor increase along with increase in torque.But it increase slowly due to overloading and chances of reverse rotation increase.

Speed Load Characteristics

Speed load characteristics of differential compound motor is given below by a curve between speed and load.form curve it is looking that when load current increase the speed of the motor also increases with the load current.Reason for this increase in speed of the motor is reduction in resultant magnetic flux.  

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