Electrical and Electronics Knowledge

Electrical and Electronics Knowledge

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05/02/2022

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Photos from Electrical and Electronics Knowledge's post 08/12/2021

How commutator are convert AC current into DC current or DC to AC For More details click here
http://surl.li/axend

To understand how commutator converts from AC to DC, first you need to understand how the commutator work and what is commutator ?

Introduction :

The commutator is of cylindrical shape and is made up of wedge - sheet of mica. The segments are held together by means of two 'V' shape rings that fit into the V– grooves cut into the segments. Each armature coil is connected to the commutator segment through riser.

It is an important part of the DC machine and the major purpose is

1. It connects the rotating armature conductors to the stationary external circuit through carbon brushes. Carbon are use for brushes because carbon are good conductor material and carbon provide lubrication effect on the commutator.

2. It convert the alternative current induced in the armature conductors into unidirectional current in the external load circuit in generator action where as it convert the alternating torque into unidirectional (continuous) torque produced in the armature in motor action.

For more information click here http://surl.li/axend

31/10/2021

Star(Y) Delta(∆) Connection of electrical motor

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30/10/2021

The speed of Electricity ?

24/09/2021

Electrical and Electronics Knowledge updated their address. 26/08/2021

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Electrical and Electronics Knowledge updated their website address.

What is Radio Communication System ? Electrical and electronics knowledge ~ Electrical & Electronics Knowledge 05/07/2021

What is Radio Communication System ? Electrical and electronics knowledge ~ Electrical & Electronics Knowledge

What is Radio Communication System ?
See more click here this link https://jana155.blogspot.com/2021/07/what-is-radio-communication-system.html?m=1


Radio communication system means the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic field that pass though the air and vacuum of space . Information is carried by systematically changing (modulating) some property of the radiated such as amplitude, frequency.

Radio communication furnishes a very useful and interesting application of electronics. There are two types of radio communication, namely,

1. Radio telegraphy.
2. Radio telephony.

See more click here this link https://jana155.blogspot.com/2021/07/what-is-radio-communication-system.html?m=1

What is Radio Communication System ? Electrical and electronics knowledge ~ Electrical & Electronics Knowledge What is Radio Communication System ? Electrical and electronics knowledge

Photos from Electrical and Electronics Knowledge's post 31/01/2021

What is Voltage Amplifier and Current Amplifier?
See more click here https://jana155.blogspot.com/2021/01/what-is-voltage-and-current-amplifier.html?m=1
Voltage Amplifier :-

A voltage amplifier is an amplifier that meets the demand for how much power it will receive in a circuit and how much input or output voltage it will require in that circuit.
A voltage amplifier is required to amplify signal voltage in situations where the power consumed by the load impedance is not of prime concern.

The amplifiers in the pre-amplifying stage of a radio receiver are voltage amplifiers.

Current Amplifier :-
A current amplifier is an amplifier that meets the demand for how much power it will receive in a circuit and how much input or output current it will require in that circuit.

An ideal current amplifier is defined as an amplifier for which the proportionality factor between the output current and the input signal current (the current gain ) is independent

Frequency Amplifier :

An frequency amplifier means to amplify any frequency like audio, video and radio.
And this amplifier are divided into three parts -

1. Audio frequency amplifier.

2. Video frequency amplifier.

3. Radio frequency amplifier.

See more click here this link https://jana155.blogspot.com/2021/01/what-is-voltage-and-current-amplifier.html?m=1

02/01/2021

What is Power Amplifier ?
See more click here https://jana155.blogspot.com/2021/01/what-is-power-amplifier-why-power.html?m=1
A power amplifier usually electronic amplifier designed to increase the magnitude of power of a given input signal. It's constitutes the last stage of a multistage amplifier system and serves to supply sizable power to the loads of output devices like speakers, headphones, RF transmitter and so on.

The efficiency of a power amplifier is the ratio of the ac output power to the power delivered by the supply source. The efficiency increased from classes A to class C via class AB and class B Amplifiers.

The operations of classes AB, B and C are nonlinear and so generate harmonics of the signal frequency at the output current. Two methods are employed to reduce or eliminate the harmonic components. One method employs the push-pull connection over a wide band of frequencies in the low or AF range.

The second method uses a parallel resonant circuit as the amplifier load over a narrow band of frequencies in the RF range. Class C operation of power amplifiers is not used in the AF range owing to the excessive harmonic distortion and the requirement of a parallel resonant circuit.

Why Power amplifier is used ?

This is because they are all the power MOSFET power BJTs are using in this particular power amplifier general transistor has some limitation to amplify in the range of temperature on the parameter of temperature on the parameter of voltage on the parameter of current and so on.

Purpose of a Power Amplifiers :-
The purpose of a power amplifier is to convert dc power from the supply source to ac signal power at the load. A special bipolar transistor, referred to as a power transistor, is employed as the active amplifying element in a power amplifier.
The special features of a Power transistor are as follows :

09/11/2020

What are the characteristics of transformer oil ?
See more click here https://jana155.blogspot.com/2020/11/what-are-characteristics-of-transformer.html?m=1
The properties of transformer oil or switch gear oil are recommended in IS 335 : 1963. The fresh dielectric oil has a pale yellow colour.

Characteristics of transformer insulating oil :

1. Is should have dielectric strength not less than 40 KV (r.m.s.) in the transformer tank for new untreated and for the gap of 4 mm of the electrodes.

2. If should be free from moisture contents and water vapour.

3. The oil should be perfectly clear and pale in colour, transparent and free from suspended matter of sediments.

4. Acidity contents should be very low in the oil.

5. It should have high flash point i.e., 104°C and lower points as per specifications laid down.
See more click here this link https://jana155.blogspot.com/2020/11/what-are-characteristics-of-transformer.html?m=1

Photos from Electrical and Electronics Knowledge's post 02/11/2020

How does the moisture is controlled in breather fitted on distribution transformer? Changing of breather ? https://jana155.blogspot.com/2020/11/how-does-moisture-is-controlled-in.html?m=1

The breather is a box containing calcium chloride or silica gel to absorb moisture of air entering the conservator as it is a well

known fact that the insulating property of the transformer oil is lost if a small amount of moisture enters in it , so dry air is allowed to pass in through this breather.

The transformer oil should not be allowed to come in contact with atmospheric air. A small amount of moisture causes a great decrease in the dielectric strength of transformer oil.

When oil level in the oil conservator changes, air moves in and out of the conservator. This action is known as breathing.

Breather contains silica gel or some other drying agent such as calcium chloride. This ensures that only dry air enters the transformer. Dry silicas gel is of blue colour. It turns pale pink as it absorbs moisture. The wet silica gel can be regenerated by drying.

Some major point to changing of Breather :-

1. Remove the wing nuts supporting the body.

2. Glass container should be squarely fitted on its gasket, then pour re-activated or fresh Silica Gel into the container upto a level 1/4 inch from the top.

3. Fix the assembly to the top plate with inspection window facing outward from the transformer and secure it with the wing nuts. Ensure that top gasket is in position.

4. Transformer oil should be poured into the oil cup until it overflows through the screw hole and fix it to the assembly with the nut.

5. Silica Gel is re-activated by applying heat to it or heating it in oven unit its colour is restored to blue. While baking Silica Gel temperature should not exceed 150°C.
See more click here https://jana155.blogspot.com/2020/11/how-does-moisture-is-controlled-in.html?m=1

Photos from Electrical and Electronics Knowledge's post 29/10/2020

How often should transformer oil be tested?
See more click here https://jana155.blogspot.com/2020/10/how-often-should-transformer-oil-be.html?m=1
Testing of Transformer Oil :
In order to determine the suitability of the oil, following tests should be carried out before using the insulating oil.

1. Flash point or Breakdown test.
2. Crackle test.
3. Sight test.
4. Acidity test.

1. Flash point or Breakdown test :-
This test is performed to check the dielectric strength of the transformer oil.
The point at which the spark occurs and Transformer trip is known as flash point.

The test is performed in the oil testing set. The sample of oil is drawn from near the top and bottom of the transformer and tested in the oil testing set. A lower than 30KV dielectric strength of a 4 mm gap of electrodes would indicate presence of moisture in the oil. The actual testing is done as follows.

The transformer oil testing equipment are –
A-Main Switch.
B- Main indicating lamp.
F or H- Push button.
H, T or G- Push button off.
J- Voltmeter.
O- Motor stop switch.
R- Electrodes.
1- Bakelite disc.
2- Electrodes.
3- Handles.
4- Acrylic Cover.
5- Variac K**b.

The gap of the electrodes is first checked with a gauge. The cup is then filled with sample oil to be tested upto about one cm above the electrodes. The cup top is covered with a clean glass plate.

The supply is switched on and voltage is raised gradually by the Variac, the stage comes when the final breakdown of the oil takes place and the circuit breaker is got tripped which disconnects the transformer from the main supply.

This value is noted down which must be 30 KV (r.m.s.) for 4 mm ± 0.02 gap and 20 KV (r.m.s.) for 2.5 mm gap. The test is performed with two or three consecutive samples of oil turn by turn. With interval of one minute to allow the bubbles to escape. Average of all subsequent tests is considered as the breakdown voltage of oil sample.

2. Crackle Test :-

The test is performed to check the presence of moisture in the insulating oil . To perform this test, a sample oil of 250 ml is taken in a beaker. One iron rod of 12.5 mm is made red hot and dipped in this sample of oil.

If there is any hissing sound coming through the oil in the breaker, it indicates the presence of moisture contents in the oil which will be considered not suitable for the use.

3. Sight Test :-

As per ISI 1896 - 1967 this test can be performed by taking water in the beaker and bent tube is filled with sample oil. The level in the tube of the oil should not be less than 35 mm by level of water in the beaker.

Close the end of the tube and fix it on the stand by dipping into water. If the bubbles appear at the jet, then it will indicate the presence of moisture contents in the oil. This test is rarely used because the oil testing set is not easily available in the laboratory.

4. Acidity Test :-

It is defined as the measure of free organic and inorganic present together in the oil. It is expressed in terms of the number of milli-grams of potassium hydroxide required to neutralize the total free acid in one gram of material.
See more click here https://jana155.blogspot.com/2020/10/how-often-should-transformer-oil-be.html?m=1

Photos from Electrical and Electronics Knowledge's post 20/10/2020

How does a 3–Phase Induction Motor Work ?
See more click here https://jana155.blogspot.com/2020/10/how-does-3phase-induction-motor-work.html?m=1

Generally speaking , let us consider one conductor on the stationary rotor.

Let, this conductor be subject to the rotating magnetic field produced when a three-phase supply is connected to the three-phase winding of the stator.

Let, the rotation of the magnetic field be clockwise. A magnetic field moving clockwise has the same effect as a conductor moving anticlockwise in a stationary field.

By Faraday's law of electromagnetic induction, a voltage will be induced in the conductor. Since the rotor circuit is complete, either through the end ring or an external resistance the induced voltage causes a current to flow in the rotor conductor. By right-hand rule we can determine the direction of induced current in the conductor.

Since the magnetic field is rotating clockwise, and the conductor is stationary we can assume that the conductor is in motion in the anticlockwise direction with respect to the magnetic field. By right-hand rule the direction of the induced current is outwards

The current in the rotor conductor produces its own magnetic field.

We know that when a conductor carrying current is put in a magnetic field a force is produced on it. Thus, a force is produced on the rotor conductor. The direction of this force can be found by left-hand rule.

It is seen that the force acting on the conductor is in the same direction as the direction of the rotating magnetic field. Since the rotor conductor is in a slot on the circumference of the rotor, this force acts in a tangential direction to the rotor and develops a torque on the rotor. Similar torques are produced on all the rotor conductors.

Since the rotor is free to move, it starts rotating in the same direction as the rotating magnetic field. Thus, a three-phase induction motor is self-starting. Since the operation of this motor depends upon the induced voltage in its rotor conductors, it is called an INDUCTION MOTOR.

Speed And Slip of 3-Phase Induction Motor :

An induction motor can't run at synchronous speed. Let us consider for a moment that is rotor is rotating at synchronous speed. Under this condition, there would be no cutting of flux by the rotor conductors, and there would be no generated voltage, no current and no torque.

The rotor speed is therefore slightly less than the synchronous speed. An induction motor may also be called as 'Asynshronous motor' as it doesn't run at synchronous speed.

See more click here https://jana155.blogspot.com/2020/10/how-does-3phase-induction-motor-work.html?m=1

Photos from Electrical and Electronics Knowledge's post 29/09/2020

Which type of rotor are used in three phase induction motor ? and construction of induction motor
See more click here https://jana155.blogspot.com/2020/09/which-type-of-rotor-are-used-in-three.html?m=1

Three phase Induction Motor Construction :-
Three-Phase induction motor is the most popular type of a.c. motor. It is vary commonly used for industrial drives since it is cheap, robust, efficient and reliable.

It has good speed regulation and high starting torque. It requires little maintenance. It has a equitable overload capacity.

Construction:
3 phase induction motor is essentially consists of two parts —

(1) Stator and
(2) Rotor

The stator is the stationary part and rotor is the rotating part.

Stator :

The stator is build up of high grade sit still aluminium to reduce eddy-current losses.
The aluminium are slotted on the inner periphery and are insulated from each other.

These laminations are supported in a stator frame of cast iron or fabricated steel plate. The insulated stator conductor are placed in these slots. The stator conductor are connected to form a three phase winding. The phase winding may be either star or delta connected.

Which type of rotor are used in three phase induction motor ?

Rotor :

The rotor is also built up of thin laminations of the same material as stator.
The laminated cylindrical core is mounted directly on the shaft or a spider carried by the shaft.

These laminations are slotted on their outer periphery to receive the rotor conductors. These are two types of induction motor rotors.

See more click here https://jana155.blogspot.com/2020/09/which-type-of-rotor-are-used-in-three.html?m=1

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