Tuesday, April 28, 2020
Dc Series Motor
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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Thursday, April 23, 2020
Dc Motor
Motor
A Electrical Machine which changes the electrical energy into mechanical energy is called Motor.
On the basis of electrical supply .They are of two types:
- AC Motor
- Dc Motor
Dc Motor
- Dc Motor is run by Dc Source and covert Dc electrical energy into mechanical energy.
- When a current carrying conductor is placed on a magnetic field, it will experience a force which can be determined by Fleming's Left Hand Rule.
- Dc Motor are subdivided into different category by changing the connection of armature winding and fielding winding.
Construction:
Yoke:
- The Outer Frame/Yoke is a hollow cylinder of cast iron or unlaminated ferromagnetic material and protecting cover to the machine.
- Yoke is stationary and no flux variation take place ,hence no iron loses. So, no need of lamination required.
- It provides mechanical support and path for the pole flux and carry half of the magnetic field flux and other half by the armature core.
- Field core consist of pole core and pole shoe and made up sheet steel lamination's that are insulated from each other to reduce eddy-current losses.
- Pole shoe are fixed to the pole core appropriately having a curved surface towards center.It supports the field coils and increase the cross section area of the magnetic circuit and reduces its reluctance.
- Each pole has one or more field coil to produce magnetic field.
Armature:
- It consists of a shaft upon which a laminated cylinder is mounted.The armature core has grooves or slots on its outer surface.
- Armature conductor is located on this slots.The connected arrangement of conductors is armature winding.
- Armature core provides the low reluctance path for the magnetic field.It is made up of thick lamination of silicon steel to reduce the eddy-current losses.
Wednesday, February 6, 2019
Basic of Electricity
Who invented the electricity? , where does the electricity come from?
This type of question disturbs you a lot even if you are not a science student. Lets clear the doubt, we will start with the basic.
This type of question disturbs you a lot even if you are not a science student. Lets clear the doubt, we will start with the basic.
Electric Charge:
Atoms are made up of electron, proton and neutrons. When an atom has more electron than proton it is negatively charged and when the proton is more, it is positively charged. When both electron and proton are in same in number it is said to be electrically neutral.
These charges experience a force when placed in an electromagnetic field.
The amount of charge in one electron. is 1.6×10−19 C and One coulomb of charge is approximately equal to 6.24×1018 .
electrons.Electric current:
Many students think electric current is just only the flow of charged particles but it is not the complete definition. Electric current is the moving of charged particles per unit time.
Current is not a thing that was invented it is a natural force which is present in nature in pure form.
There will never be a shortage of electricity in the world but we didn't have sufficient storage material to store the electricity for a longer time.
In June 1952, Benjamin Franklin was the first man who connection between lightning and electric current by flying a kite, lightning is only an electrical discharge.
The kite with an iron point on the top and key at the end of the rope, the iron at the top of the kite is pointed to make resistive less path for current to flow through the iron point and currently comes down through the rope. He concluded that the lightning is the discharge of electric current and consist of positive and negative charges particle.
In 1880, Thomas Edison was the first man who supplies Dc electric current to every home starting with the street light. At the same time, Nikola Tesla came up with Ac current which has more advantage than the Dc current and wins the war of current, from that time Ac current is preferred.
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