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Rotor of Squirrel Cage Induction Motor

Wednesday, August 11, 2021

Reluctance Motor

Posted by Pranshu Bahuguna, on August 11, 2021

Reluctance Motor

Before explaining about the motor let me clear you what is reluctance. 

Reluctance:

It is the opposition offer to the magnetic force analogy to resistance in electrical circuit. It is the opposition to the flow of magnetic flux.
Reluctance is the ratio of the Magnetomotive Force to the Magnetic Flux . 
The SI unit of reluctance is ampere turns per weber (At/Weber)

Reluctance motor is a unexcited single phase Synchronous Motor, which runs on the synchronous speed 

Construction:

Stator:

It consist of two Winding:
  1. Main Winding 
  2. Auxiliary Winding
To produce revolving magnetic fields in single phase motor we need two windings in reluctance motor or any type of the single phase motor.

Rotor:

The rotor looks like single phase squirrel cage motor which have a symmetrical cutouts and have no winding on the rotor side, and have slots on the outer side 

Working :

On giving supply to the winding the motor starts running at a speed lower than the synchronous speed (Ns=120f/P) and speed of 4 pole synchronous motor is 1500 rpm.
when we supply the motor, the motor runs at speed less than synchronous speed Nr which is less than 1500rpm.
When the motor attain a speed ,as there is air gap on the rotor side which opposes the flux, and there is development of the reluctance torque on the poles and do the magnetic locking with poles. Afterwards the motor gets lock with poles and starts moving at a synchronous speed.

Torque angle :

The angle between the stator pole and rotor pole of opposite polarity as the angle between then increases the reluctance also increases. The maximum reluctance toque attain at 45degree.

Note:

When we add  mechanical load magnetic angle between the stator and rotor changes but the motor always try to run at synchronous speed but when we add more load then it will be out of synchronism and motor will be stop.
The reluctance motor is a self starting motor which runs at a synchronous speed without any external excitation. 
Reluctance Motor has a constant speed characterstics.







Tuesday, December 15, 2020

Transmission Line and Feeder

Posted by Pranshu Bahuguna, on December 15, 2020

Four Types Of  Distribution Feeders Systems:

  • Radical 
  • Parallel Feeders
  • Ring Main
  • Meshed

 Radical :

Radical is the simplest and least expensive to construct. This is used when the generating station is at the center and different feeder radiate to the different direction and power flow is only in one direction.

So, it has one feeder line for the group of customer. If some problem such as power failure, short circuit arises at one spot, entire feeder  line will go down.

Parallel Feeders :

This feeders system is used when we need continuous power supply for 24 hours. In this feeder system a parallel separate feeder line is followed with the main feeder line. Whenever there is a fault in the main line, the power didn't cut at the consumer and is fed from the separate feeder line, this is the main advantage of the parallel feeder over the radical feeder.

The main disadvantage is the construction cost of the parallel feeder is more. 

Ring Mesh :

Ring mesh is quite similar to the parallel feeder but in this the distribution transformer is fed up with two different feeder, from two different path, and form a ring structure. This system is reliable as the distribution transformer is fed up with two feeder and if the fault comes in one feeder. The continuity supply of Electrical power didn't stop.

Meshed System:

When the ring meshed system is energized by two or more generating station is known as meshed system.

Types of Transmission line on the basis of distance:

  • Short Transmission Line ranges from zero to 80 Km and operating voltage of 0 to 20 Kilovolt. Shunt capacitance is so small that it can be omitted entirely with little loss of accuracy.

  • Medium transmission  line ranges from 80 to 200 km and operating voltage of 20 to 100 kilovolt.
  • Long transmission line ranges from 80 to 200 km and operating voltage above 100 kilovolt. Mho relay is used in long transmission line.

A small LT line is a lower voltage Line which is 230 volt for single phase supply and 400 volts for 3 phase supply.

HT Line is for High Voltage Line which starts from 11 kV, 33 KV, 220 KV, 400 KV and more.

Note:

A Transmission line is used in reference to the transmission system and used for sending Electrical power from the generating Station to the substation. Power is Transmitted via transmitted line to the substation, where transmission voltage are more than 132KV

A Feeder is used with respect to the distribution system and used for sending power from substation to the consumer/load end. 

Characteristic Impedance

When the receiving end voltage is equal to IZ, the current and voltage waves are travelling in one direction, without any reflection of either current and voltage waves. The line is terminated in its characteristics impedance Zc and line is known as infinite line.

Ferranti effect.

When long or medium transmission line is open circuit or on light load the receiving end voltage is greater than the sending end voltage, this effect of increase in the voltage at the receiving end is known as the Ferranti effect. This effect is absence in short transmission line because of negligible shunt capacitance.

Monday, November 9, 2020

TRANSISTORS AS A SWITCH

Posted by Pranshu Bahuguna, on November 09, 2020

Transistors 

In 1947,The world of electronic devices is completely changed by the two physicists
John Bardeen and Walter Brattain when they made the first working device on point contact transistor.
Transistor are the semiconductor  device having three terminals, used as a switch or to amplify a current. They are very light in weight around 1gram or less and very small in size. The phone that you are carrying is light in weight and have small size that fit in your hand  because of the transistors.
Transistors can used as a switch in digital electronics and as an amplifier in the analog electronics. 

Transistors have 3 terminal:
1.Emitter
2.Base
3.Collector

Emitter is the source of charge carrier and that is why it is heavily doped. 
Base is lightly doped and very thin in size 
https://electricsknowledge.blogspot.com/2020/11/transistors_9.html
Transistor
Collector is moderately doped and wider in size than base and emitter region because collector main's job is to collect charge carrier from base and emitter region



Active region:


When the base emitter region is forward bias and collector and base region is reversed  bias. 
For this condition :
Base voltage must be higher than emitter voltage and Vbe =0.7 Volts
Collector voltage must be higher than base voltage so than collector voltage is higher than the other region voltage. 
The base current is directly proportional to the collector current. 

Transistor act as  a switch:

Transistor can act as a solid state switch that doesn't require any moving part, it act as a on/off switch just by sending a base signal.

For transistor to act as a switch:
  • Emitter is connected to the Ground.
  • Base is connected to the on/off signal with a  resistor
  • Collector is connected to the 5v supply.
Resistor is connected with the base terminal because base current should not be of high ampere, it can damage the transistor.

When a base current is flow through the transistor. So, it will create a path for the Emitter electron to flow through base region  to the  collector region and the current will easily flow through the collector region to the emitter region and act as a short circuit path. Transistor act as ON switch.
When base current is remove the collector current can't cross the base region and act as a open circuit or OFF switch.

So, in this way transistor can act as a switch



Difference between Earthing and Grounding.

Posted by Pranshu Bahuguna, on November 09, 2020



Earthing:

Earthing means connection of the non current carrying part of electrical equipment to the Earth. 

Advantage:

  • During fault condition if current flows through the equipment's, the chances of getting shock to the electrician will increases, if Earthing is done then all the current will be drawn to the Earth because equipment is in some potential during fault condition  and Earthing point is in zero potential ,then all the current will be drawn to the Earth and chances of getting shock will decreases. 
Earthing and Grounding

Grounding:

Grounding is connection of the neutral wire(which carry return current)  to the Earth.

Application:

  • Grounding is done of neutral point of the star connected transformer.
  • Grounding wire of lighting arrester is connected to the Earth which provide current path to the Earth. 
  • During fault condition all the excess current is transfer to the Earth to the safety of the electrical equipment's

Note:

Ground in electronics doesn't mean wire is physically connected to the Earth it simply refers to the zero potential from the other points.


Thursday, October 8, 2020

Power Factor

Posted by Pranshu Bahuguna, on October 08, 2020

 Power Factor

Power factor is normally the phase difference between the voltage and current. Power factor is due to the inductive nature of the circuit, however, in resistor the voltage and current are in phase with each other. So, the power factor of the resistive load is unity and reactive power is zero. All the power is active power in resistor. Power Factor is the cosine of active power and he reactive power and maximum value of cosine is one. Therefore the power factor of a load can never be more than one.

  • Power factor is said to be lagging when the current lags the voltage by some angle, due to the inductive nature of the load. 
  • Power factor said to be leading if the current leads the voltage by some angle, due to the capacitive nature of the load.

Active Power:

Active power the main power which is consumed by the load. The main components of power which is used by the ac circuit to do some work. It is measured in KW.

Reactive Power:

Reactive power is the component of the total power which is travel along the active power but not used by the load. It  just travel back and froth in the load. It is used to establish the magnetic field in the motor or other alternating current equipment.

Apparent Power:

The total of the active power and the reactive power is known as apparent power
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