Dc Series Motor
What Is Dc Series Motor?
When the armature winding is connected in series with the field winding which is energized by the dc source is Dc Series Motor.
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| Dc SERIES MOTOR |
Working of Dc Series Motor
- Current is same on both,series field winding and armature winding.
- Flux produce is directly proportional to the field winding current.
Φ∝Ise
By KCL,
Itotal=Ise=Ia
Where,
Ise =Series Field current
Ia =armature current
By KVL,
V=Eb+I(Ra+Rse)
Where,
V=Terminal Voltage
Eb=Back E.M.F
I=Current
Ra=Armature Resistance
Rse=Series Winding Resistance.
Back E.M.F:
When the motor rotates,armature coil cut the magnetic flux,which induces an e.m.f in it known as the back e,m,f.
The back e.m.f opposes the applied voltage and always is less than applied voltage.
Eb=NPZΦ/60A
Characteristics Of D.C Series Motor:
- Speed/Armature current Characteristics:
The Motor speed N in series motor is inversely proportional to the main field flux.
N ∝ 1/Φ
The flux Φ is produce by the current flowing in the series field winding.Therefore flux is directly proportional to the current flowing through it.
Φ ∝ Ise ∝ Ia as Ia = Ise
So, the speed is inversely proportional to the armature current.
As,
The motor speed is inversely proportional to the armature current. The no load speed of motor become very high,which may damage the motor due to the centrifugal forces,because draws a small no load current.That"s why dc series motor never runs at no load or light load.
- Torque/Armature Current Characteristics:
Torque(T)=KΦI
So,
T ∝ ΦIa
As,
Φ ∝ Ia, Before magnetic saturation
T ∝ Ia^2
After Saturation,Flux become independent of Armature current
So,
T ∝ Ia
At Light Loads,Torque is proportional to the square of armature current.Also known as Electrical Characteristics.
Advantages:
- The series motor has the highest starting torque than other Dc Motor.
- During an overload,motor easily achieves high torque and draws less current from the source.
- Starting torque for the motor is high therefore it is widely used in electric traction and in crane application.
NOTE:
Static Characteristics:
Static Characteristics of an instrument are the quantity that slowly varies with the time or does not changes(remains constant).
Dynamic Characteristics:
Dynamic characteristics of an instrument are the quantity which rapidly changes with the time.
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