Tuesday, September 22, 2020
Single Phase Induction Motor
Single Phase Induction Motor
The single phase induction motor is Classified into 4 motor
- Split Phase Induction Motor
- Capacitor Start Induction Motor
- Capacitor Start Capacitor Run Induction Motor
- Shaded Pole Induction Motor
Split Phase Induction Motor
The stator has two winding i.e Main winding/Running winding and Auxiliary winding/Starting winding. A centrifugal switch is connected in series with the auxiliary winding,to disconnect the auxiliary winding from the main winding when the motor achieves a speed of 70-80% of synchronous speed.
Working:
Auxiliary winding is 90 Degree in phase with the main winding.The running winding is inductive in nature that means current lags the voltage by an angle and the auxiliary winding is resistive in nature that means the current and voltage are in phase with each other.
To create a phase difference between 2 winding the starting winding must carry high resistance.
The result of these 2 current i.e Itotal which produces the rotating magnetic field which rotates in one direction.
As the starting and main current splits from each other by some angle hence this motor is called Split Phase Induction Motor
Advantages:
- Motor have low starting Current
- Motor have low starting Torque
- Motor are used in fans, blowers, centrifugal pumps
Application Of Single Phase Motors:
Shaded Pole induction motor are available to run with speed as low as one r.p.m.
Universal Motor/Single Phase Series Motor is used for the purpose of high speed and speed control is required. such as vacuum cleaners, drill machines.
Test on Dc Motor
Swinburne Test
This test is used to determine the efficiency, losses and temperature ries on the dc machines. This test is perform on the large shunt dc machines.
Hopkinson Test
This test is perform with the help of two shunt machine. Both machine are couplled together mechanically and electrically.
One act as a motor and other as a generator. The output of the motor is connected to the input of the generator and output of the generator connected to the input of the motor.
Saturday, May 16, 2020
Sensor and Transducer
Transducer:
Transducer is a device that converts one form of signal into the other form of signal.
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| Transducer |
The input is given to the Sensor and the output of sensor is the input of Processor.The combine process of sensor and processor is a Transducer in which the sensor converts the physical quantity into electrical signal and processor continue the further process.
Now the Processor output electrical signal is given to the Actuator which coverts the electrical signal to the mechanical works,which is also an example of transducer.
Examples:
Microphone: Convert voice to Electrical signal
Speaker: Convert Electrical signal into Sound
Antenna: Converts Electromagnetic energy into electrical and vice versa
Strain Gauge : Convert strain to electrical. Strain gauge is a sensor that converts strain(Force) into the electrical signal,its resistance changes with the applied force on it and force magnitude can be easily measured.
Sensor:
Sensor is a device that converts physical quantity into electrical signal.
Example: Temperature and humidity sensor- DH22,
PIR Sensor: Passive Infrared Sensor is an Electronic device that measures infrared light radiation emitting from the object in its range.Generally, PIR can detect any Human/Animal movement in a range,the sensor doesn't emit any energy but passively receives and detect infrared energy from the environment.
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| PIR Sensor |
Ultrasonic Sensor: It is an optical sensor and can detect how far an particular object is placed.It uses a transducer to send and receive ultrasonic sound waves that gives an approximation distance of the object from the sensor.
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| Ultrasonic Sensor |
LDR Sensor :Light Dependent Resistor has a variable resistance which is the function of intensity of light falls on the surface of sensor. Its resistance decrease with the increase in the intensity of light falling on it. LDR can be used in the street light to automatically switchs on and off the lights when it requires.
LED: Led is a semiconductor which emit lights when current flows through it.
Led has two terminal:
Anode which is long terminal and positive in nature.
Cathode which is short and negative in nature.
Current aways flows from the anode to Cathode in LED and never in the opposite terminal.
The operating voltage of LED is around 1.8 to 3.3 volts it varies by the color of LED.Current varies from 10mA to 20mA which maximum current capacity of LED. It will burn out, if current more than 20mA goes in the LED.
Always, a Resistor is connected in series with LED to limit the current through the LED. The resister used is known as ballast resistor
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.
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