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Star - Delta Starter Working

Star - Delta Starter 

To start a large induction motor we use star - delta starter because large induction motors(cage type) with delta connected stator when started directly on line it produces large starting current surges which causes fluctuations in voltage on supply line. To prevent this we run induction motor at reduced voltage at the start of induction motor and later on after getting require speed we operate induction motor at full supply voltage for this purpose we use star delta starter.

Working Principle Of Star - Delta Starter:

As discussed above to reduce fluctuations in voltage on supply line we need to reduce starting surge currents so we need to reduce the voltage at the start of induction motor for this purpose we firstly connect the stator windings of induction motor in star connection and later on we connect the stator windings in delta to operate at full supply voltage. See the below circuit diagram how the star - delta starter is connected to induction motor.

Connection diagram of star - delta starter:

star delta starter control circuit diagram
During start position of switch the stator windings are connected in star as shown in the following figure.

Now the induction motor gradually picks up it's speed. When the speed becomes 80 percent of its rated speed then the switch moves to run position as a result stator windings get connected in delta as shown in the below figure.

Theory And Calculations Of Star - Delta Starter:

To understand how voltage is reduced by star connection of stator windings see the below calculations.

In star connection the phase voltage is 1/√3 times of line voltage as the torque is directly proportional to square of voltage applied the torque is reduced to 1/3 times than the torque produced by starting with direct delta connection.

Let,

VL be the line voltage.

V1 is the phase voltage.

Istyp be  starting current per phase when the stator windings are connected in star.

Istyl is the starting line current when the stator windings are connected in star.

IstΔp is the starting current per phase by direct switching with the stator windings connected in delta

IstΔl is the starting line current by direct switching with the stator windings in the delta.

IscΔp is the short circuit phase current by direct switching with the stator windings in the delta.

Ze10 is the standstill equivalent impedance per phase of the motor, referred to the stator


In star connection,  line current will be equal to phase current.
In delta connection, the line current is equal to the √3 times of the phase current. so we get,

This shows that with star delta starter, the starting current from the main supply is one-third of that with direct switching in the delta.
This shows with star delta starter, the starting torque is reduced to one-third of the starting torque obtained with the direct switching in the delta.
Here,
IflΔp is the full load phase current with the winding connected in delta. But
So the above equations show how voltage and torques are reduced with star delta starter than direct delta starting.


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Electrical Braking of DC Motors | What is Braking? Types of Braking

Electrical Braking Of DC Motor

We have two types of braking they are mechanical braking and electrical braking. We prefer electrical braking to stop a dc motor rather than mechanical braking because electrical braking has more advantages than mechanical braking they are mentioned below:

Advantages of electrical braking over mechanical braking:

1. Electrical braking is fast and effective than mechanical braking

2. Electrical braking doesn't involve high maintenance cost unlike mechanical braking. In mechanical braking we need to replace break shoes periodically which involves high maintenance cost.

3. Amount of heat generated in electrical braking is very much less than that of heat produced due to mechanical braking. This heat produced in mechanical braking at brake shoes leads to failure of brakes.

4. In electrical braking a part of electrical energy is returned to supply which helps in reducing the running cost.

5. Using electric braking the capacity of the system like higher speeds, heavy loads can be increased which cannot be obtained through mechanical braking.

Because of the above advantages we use electrical braking to stop dc motor instead of using mechanical braking.

Now let us see about electrical braking in detail.

Types of electrical braking :

There are three types of electrical braking. They are:

1.Regenerative Braking.

2.Dynamic Braking or rheostatic braking.

3.Plugging.
Here let us see how electrical braking is applied to stop dc shunt motor and dc series motor.

Electrical braking of dc shunt motor:

Each of the three electrical braking methods to stop dc shunt motor are discussed clearly below.

Regenerative braking of dc shunt motor:

In this type of braking if the load on the dc shunt motor increases the speed of motor above the no load speed at constant excitation then the back emf (Eb)produced will be greater than the supply voltage at this stage dc shunt motor acts as generator since the motor armature current reverses its direction. So now it supplies power to the line. Due to reversal of direction of armature current as Eb  > V, armature torque is reversed and speed falls until Eb  becomes less than V so the motor doesn't completely stop in regenerative braking only speeds above no load speeds are decreased and controlled. Regenerative braking is clearly shown in the following figure.

Dynamic braking or rheostatic braking of dc shunt motor:

In dynamic braking we disconnect the armature of dc motor from the supply and connect a resistor to it while the field is connected to the supply as shown in the following figure.
As the armature is disconnected from the supply and connected as shown above now it acts as generator and kinetic energy stored in rotating parts and connected load is converted into electrical energy and is dissipated through rheostat as heat energy and dc shunt motor stops. This is not an efficient method because all the generated energy is dissipated as heat energy. 

Plugging of dc shunt motor:

In this method the terminals of the armature of dc motor or supply polarity is reversed. So the torque direction gets reversed and hence back emf Eb and supply voltage V will be in the same direction. So now voltage will 2V which involves high inrush current to prevent this we add a resistance as shown in the following figure.
Now the motor speed decreases slowly and stops, at this point an external device is required to cut off supply as soon as motor comes to rest.Plugging gives greater braking torque as compared to rheostatic braking or dynamic braking.

Electrical braking of dc series motor:

Each of the three electrical braking methods to stop dc series motor are discussed clearly below.

Dynamic braking or rheostatic braking of dc series motor:

In this the armature is disconnected from the supply and current through the armature reverses its direction and field remains connected to the supply. Care should be taken such that current direction through field doesn't changes for this purpose we reverse the field .Now dc series motor acts as dc series generator. This can be shown in the following figure.
Now the kinetic energy stored in rotating parts and connected load is converted to electrical energy and dissipated through rheostat as heat and dc series motor stops.

Plugging of dc series motor:

In this method terminals of the armature or supply voltage are reversed and a resistance is added to control magnitude of braking torque. By this dc series motor stops. The figure is shown in the following diagram.Plugging gives greater braking torque as compared to rheostatic braking or dynamic braking.

Regenerative braking of dc series motor:

Regenerative braking with dc series motor is not possible because increasing in excitation causes decrease in speed. Back e.m.f Eb cannot be greater than supply voltage.So regenerative braking is not possible with dc series motor to make it possible we need to connect dc series as shunt motor. For traction motors regenerative braking is done by special arrangement as shown in the following figure. Using series motors for regenerative braking the fields must be excited separately and use stabilizing circuits. The figure shown below gives connections for regenerative braking on dc series motor.

By connecting in this way back e.m.f Eb can be made greater than V and can be run as generator and torque gets reversed and speed falls till Eb becomes less than V. Hence in this way regenerative braking is done on dc series motor.

In this post we have discussed about electrical braking of dc series and dc shunt motor.

To download this post on electrical braking of dc motors as PDF click here.
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Torque equation and torque-slip characteristics of 3-phase induction motor.

Torque Equation And Torque - slip Characteristics Of Three Phase Induction Motor

Torque - slip characteristics shows the variation of torque of 3- phase induction motor with the change in slip of  that three phase induction motor.

To understand the torque - slip characteristics let us first derive torque equation under running conditions of three phase induction motor.

Torque equation under running conditions of 3 phase induction motor:

Let us see derivation for torque equation of 3 phase induction motor.

We know that,

Torque  T = Er Ir cosϕ2 or T ∝ ϕ Ir cosϕ2

Here Er = rotor e.m.f / phase under running conditions.
         Ir = rotor current / phase under running conditions.

And Er = s E2

       Ir = Er / Zr 

Zr can be calculated from the following figure by applying pythogerous theorem.

Now we get
  
                 


From figure we get,

                          



Where S is slip which is defined as ratio of difference between synchronous speed and actual speed of rotor.

When the speed changes slip changes as a result torque also changes. Also the equation clear shows that torque changes with respect to change in slip but is not always directly proportional it always depends on the value of slip that is whether the slip value is low , medium or high. Now let us see this in detail.

Relation between torque and slip of a 3 phase induction motor:

Now let us see how torque changes with low , medium and high values of slip in detail.

Slip less than zero ( s < 0):

If the slip is less than zero it will be in generating mode. As in this mode both torque and slip are negative it should be driven by prime mover so it acts as induction generator as is it used mechanical energy and converts into electrical energy. Generally this mode of operation is not used because if the induction machine is used as generator it requires high amount of reactive power to be supplied which is expensive again.

Slip is between zero and one ( 0 < s < 1 ):

From torque equation we have torque as
T =



At s=0, T will be zero so the curve starts from origin.

Now at speeds close to synchronous speed the value of sX2 is small and an be ignored. so now torque T becomes 

T ∝ s / R2 

If R2 is constant the we have

T ∝ s so the torque graph will be approximately a straight line for low values of slip.

As slip increases torque also increases and becomes maximum when slip s = R2 / X2. To know how at maximum torque slip is R2 / X2 see the following derivation.

Condition for maximum torque:

We know torque is given by,


Now differentiate above expression with respect to slip s and equate the expression to zero. 

Put Y = 1/T for making calculation simpler we get,



So we get at maximum torque slip is s = R2/X2.

The torque at this point is called breakdown torque or pull-out torque.

Now if the slip increases further by increasing the load then R2 can be ignored. So for large values of slip we get torque as

T ∝ 1/s.

So in this region the torque slip characteristics is a rectangular hyperbola. This can be seen in the following figure.


In this mode 3 phase induction machine will be in motoring mode. At no load slip will be zero and at full load slip will be 1.

Slip greater than one ( S > 1 ):

This mode is called breaking mode. In this mode the supply voltage polarities are changed as a result motor rotates in reverse direction an stops. This help to stops the induction machine in very short time.

The overall torque - slip characteristics of 3 phase induction motor is shown in the following figure.

Today we have learnt about torque equation of 3 phase induction motor and torque slip characteristics of 3 phase induction motor.

To download this post on torque equation and torque slip characteristics of 3 phase induction motor as PDF click here.
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Current Transformer,Potential Transformer Working | Instrument Transformers

Instrument Transformers

Definition of Instrument Transformer

In heavy currents and high voltage a.c. circuits, the measurement can not be done by using the method of extension of ranges of low range meters by providing suitable shunts. In such conditions, specially constructed accurate ratio transformers called instrument transformers. These can he used, irrespective of the voltage and current ratings of the a.c. circuits. These transformers not only extend the range of the low range instruments but also isolate them from high current and high voltage a.c. circuits. This makes their handling very safe. These are generally classified as

(i) current transformers and (ii) potential transformers.

Current Transformers (C.T.) Construction: 

The large alternating currents which can not be sensed or passed through normal ammeters and current coils of watt meters, energy meters can easily be measured by use of current transformers along with normal low range instruments.

A transformer is a device which consists of two winding's called primary and secondary. It transfers energy from one side to another with suitable change in the level of current or voltage. A current transformer basically has a primary coil of one or more turns of heavy cross-sectional area. In some, the bar carrying high current may act as a primary. This is connected in series with the line carrying high current.

The secondary of the transformer is made up of a large number of turns of fine wire having small cross-sectional area. This is usually rated for 5 A. This is connected to the coil of normal range ammeter. Through this ammeter we can note down the value of current flowing through the secondary winding of current transformer. Symbolic representation of a current transformer is as shown in the figure.

Working of a current transformer and C.T Ratio:

A combination of current transformer and ammeter helps us to find out the higher values of current flowing through line. As discussed we step down the value of line current by increasing the turns in secondary winding. This shows that there is inverse relation between between primary and secondary current and the number of turns of primary and secondary. We connect an ammeter to the secondary winding of current transformer to get secondary current which is shown in the following figure.


So now we can calculate the value of current through line or primary current from the C.T ratio. 

Where,
 Np is number turns of primary winding.
 Ns is number turns of secondary winding.
 Ip is current through primary winding.
 Is is current through secondary winding.

Potential Transformers (P.T) Construction:


The large alternating currents which can not be sensed or passed through normal voltmeters and voltage coils of watt meters, energy meters can easily be measured by use of potential transformers along with normal low range instruments.

A potential transformer has two winding's namely primary and secondary. Primary winding has large number of turns and it is connected in parallel to the line(between line and ground) whose voltage is to be measured. Now the secondary has less number of turns. This is usually rated to 110 V and is connected directly to voltmeter. Through this voltmeter we can note down the value of voltage across the secondary winding of potential transformer.Symbolic representation of a potential transformer is as shown in the figure.

Working of a potential transformer and P.T Ratio:

A combination of potential transformer and voltmeter helps us to find out the higher values of potential across the line. As discussed we step down the value of primary voltage by decreasing the turns in secondary winding. This shows that primary and secondary voltage and the number of turns of primary and secondary are directly proportional.We connect an voltmeter across the secondary winding of potential transformer to get secondary voltage which is shown in the following figure.


So we can calculate the value of line voltage or voltage across the primary of potential transformer from the P.T ratio
Where,
 Np is number turns of primary winding.
 Ns is number turns of secondary winding.
 Ip is current through primary winding.
 Is is current through secondary winding.

In this post we have learnt about instrument transformers namely current transformer and potential transformer.

To download this post on instrument transformers as PDF click here


 
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3 Phase Energy Meter Working,Construction,Uses

Three phase energy meter  working,construction 

An energy meter is used to measure the energy consumed in the kilowatt hours. This is used in each and every house and industry for calculating the energy consumed by them. A 3-phase energy meter has same elements as in case of a single-phase energy meter. We see each of them in detail in this post.

Construction of three phase energy meter:

A 3-phase energy meter has following systems. This systems are same for both single phase and three phase energy meters. They are:

1. Driving System.

2. Moving System.

3. Breaking System.

4.Registering or Counting System.

Driving System:

This consists of a coil wounded on central limb of a shunt electro magnet which acts as pressure coil also known as voltage coil. This coil should have high inductance which means that inductance to resistance ratio of this coil is very high. Because of this inductive nature the current , flux will lag behind supply voltage by 90° approximately. 
        
Copper shading bands are provided on the shunt magnet's central limb to get 90° phase angle displacement between magnetic field set up by the shunt magnet and supply voltage. We have another series electro magnet on which current coil is wounded. This current coil is in series with the load so load current will flow through this.The flux produced by series magnet is proportional to and in phase with the load current. The driving system of 3-phase energy meter comprises of these elements.

Moving system:

On a vertical spindle or shaft a light rotating aluminium disc is attached. With the help of a gear arrangement aluminum disc is attached to the clock mechanism on front side of meter which helps to measure the energy consumed by load.

Eddy currents are induced due to time varying flux produced by series and shunt magnets. A driving torque is set up due to interaction between these two magnetic fields and eddy currents.

Therefore  number of rotations of the disk is  proportional to the energy consumed by the load in a certain time interval and is measured in kilowatt-hours (Kwh).

Breaking system:

To damp aluminium disc we keep a small permanent magnet diametrically opposite to both the ac magnets(parallel,series). Now this disc moves in the magnet field crossing air gap. When this happens eddy currents are induced in aluminium disc which interacts with the magnetic field and produces breaking torque.

The speed of the rotating disc can be controlled by changing the position of the brake magnet or diverting some of the flux. 

Counting system:

It has a gear system to which pointer is attached. This is connected to aluminium disc which drives this pointer. This pointer moves on the dial and gives number of times the is disc rotated.

These can be seen in the diagram given below:


A 3-phase induction motor has same four systems but they are arranged in a different way as shown in the figure given below.

This is a two element 3-phase energy meter. On a common spindle two discs are mounted and each disc has its own break magnet. Moving system drives a gear  Each unit is provided with its own copper shading ring, shading band, friction compensator, etc., to make adjustments for obtaining correct reading.

This gives construction of a 3 phase energy meter.

Working of three phase energy meter:

Now let us see how a 3 phase energy meter works.

For same power/energy the driving torque should be equal in both elements. For adjusting torque in both the elements we have two current coils connected in phase opposition and two potential coils connected in parallel. Full load current passes through current coil and this arrangement causes two torques to be in opposition and the disc doesn't move if torques are equal. Magnetic shunt is adjusted if there is inequality in torques to make the disc to stand still. Before testing a 3 phase energy meter torque balance is obtained in this way. 
            
                  Aluminium discs are acted upon by the two coils one is voltage coil and the other is current coil. Voltage coil produces magnetic flux proportional to voltage and current coil produces magnetic flux proportional to current. The voltage coil field lags by 90 degrees by using a lag coil.

                     Due to this two torques eddy currents are produced in the aluminium discs and discs rotate on a common shaft. Force exerted on the aluminium disc is proportional to product of instantaneous current and voltage. To this shaft a gear arrangement is made and a needle is attached to this gear so when discs rotates this needle moves on dial and counts the number of rotations of the disc.

                    A permanent magnet is used to produce a force in opposition and proportional to the speed of disc. When power is switched off this acts as break and makes the disc to stop rotating instead of rotating faster. Disc rotates at a speed proportional to power consumed.

Instantaneous power can be calculated by using below formula

Pi = (3600 * N) / (T * R)

where
Pi = Real power being used at that point in time in kW
T = Time (in seconds) for the disc to rotate through the N rotations or part of a rotation
N = The Number of full rotations counted.  
R = The number of revolutions per Kilowatt hour (rev/kWh) of the meter being used. 

In this way we use a three phase energy meter to calculate the energy consumed by the load.

Related to three phase energy meter:

3 phase energy meter connection diagram
3 phase energy meter price list
3 phase energy meter principle
l&t energy meter price list
3 phase energy meter specifications
3 phase energy meter l&t
3 phase electric meter price india
3 phase energy meter working

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HRC Fuse Operation,Types And Characteristics

Operation,Types And Characteristics Of HRC Fuse

Fuse is a common switch gear device which we see even at our homes. It is used to protect a device or circuit from over currents.  For household purpose usage of HRC fuse is more economical than usage of circuit breakers. Let see a clear picture about what is fuse? how a fuse works?

What Is Meant By HRC Fuse?

HRC fuse means high rupturing capacity fuse which is a modern type fuse. It interrupts current flow and protects from over current.  It is used to provide protection from short circuit damages in low voltages and medium level voltages.

Construction Of HRC Fuse:

The body of HRC fuse is made of ceramic which is highly heat resistant. It has two end caps to this caps a silver current carrying element is welded. The internal space of fuse is filled with powder material such as plaster of paris, marble, chalk, cooling media etc. as shown in the following diagram.
The above diagram shows the cross-sectional diagram of a HRC fuse.

Working Of HRC Fuse:

The fuse wire inside the HRC fuse conducts the short circuit current for a period of time safely. During this time if the fault is removed the fuse doesn't blow off. But if the fault is not removed the fuse will melt and isolates the circuit from the electrical supply as shown in the below figure.
This is how a fuse works


Controlling Of Arc In HRC Fuse:

The inner portion of HRC fuse consists of cooling medium which helps to carry normal current by the fuse wire without heating. When over current flows then heat is produced in the current carrying fuse wire because of high I2Rf loss. This heat vaporizes the silver metal element and a chemical reaction takes place between this silver metal and filling powder which produces a high resistance substance. This high resistance substance helps in arc quenching.

Characteristics Of HRC Fuse:

As discussed for normal current the fuse wire doesn't melt but when over current flows due to high I2Rf loss the fuse wire melts.So fuse wire melts faster for higher fault currents and takes more time to melt for lower fault currents. This gives the time-current characteristics of HRC fuse. This is shown in the following figure.



Types Of HRC Fuse:

We have different types of HRC fuse. They are:

1.Semi- enclosed or rewireble type.

2.Totally enclosed or cartridge type.  

3. Current limiting fuse link. 

4. Drop-out fuse.

5. Explosion fuse.

6. Striker fuse.

7. Switch fuse.

Now let us see each of them in detail.

1. Semi- enclosed Or Rewireble Type Fuse:

In this type of fuse the carrier of fuse can be pulled out and the melted fuse wire can be replaced with the new wire. Carrier has to be replaced in the fuse base. This type of fuse is used in our houses. Its diagram is shown below.

2. Totally Enclosed Or Cartridge Type Fuse:

In this type we have a fuse wire inside a totally closed container and it has metal contacts on either sides. This is further divided into two types.

1. Bolted type 2. D-type.
The above diagram is cartridge type fuse. 

3. Current Limiting Fuse Link:

This fuse link brings the current to a value lower than a prospective value.

4. Drop Out Fuse:

After fault current flows,fuse-carrier drops out. Now there will be isolation between the terminals. This diagram is shown below.

5. Explosion Fuse:

In this type of fuse the arc is quenched when produced arc produces heat which vaporizes the metal and chemical reaction is established between this vapors and powdered filling. This produces a high resistance substance which helps the produced arc to quench.

6. Striker Fuse:

This type of fuse consists of combination of a fuse and a mechanical device. This fuse releases a striker after fuse operation with a certain displacement and pressure. The following figure shows diagram of striker fuse before and after fuse operation.

7. Switch Fuse:

This is a fuse which contains both switch and fuse. This is shown in following figure.
                                            

In this post we have discussed about the operation, types and characteristics of HRC fuse.
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Differences Between Electrical Degree And Mechanical Degree

Differences between electrical degree and mechanical degree

Many people get confused about what is electrical degree and mechanical degree. Well, to get a clear idea about this we have provided the following post.

We consider an alternator with two poles once and four poles once to clearly understand about electrical degree and mechanical degree.An alternator consists of conductors on stator and poles on rotor. But for understanding purpose we consider conductors are rotating and poles are stationary. Because of relative motion between conductors and poles emf is induced inside the conductor.

Two pole alternator:

Consider a two pole alternator with a conductor as shown in the following figure.
Position 1 :At this point velocity vector V is parallel to magnetic flux lines of poles(indicated by dotted line). So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 2: Now conductor rotates to position 2.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 3: Now conductor rotates to position 3.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 4: Now conductor rotates to position 4.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

So for one complete rotation of a conductor i.e, 360 degrees there will be two maximum positions of emf this is indicated in the following figure.

Induced emf inside the alternator is sinusoidal in nature.Two maximum peaks is 360 degrees.Conductor rotation angle is mechanical degree and emf wave cycle degree for one complete rotation of conductor gives electrical degree.

Here mechanical degree is equal to electrical degree which is 360 degrees. Since for one complete rotation of conductor one complete emf cycle is produced.

Four pole alternator:

Consider a four pole alternator with a conductor as shown in the following figure.



Position 1 :At this point velocity vector V is parallel to magnetic flux lines of poles(indicated by dotted line). So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 2: Now conductor rotates to position 2.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 3: Now conductor rotates to position 3.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 4: Now conductor rotates to position 4.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 5: Now conductor rotates to position 5.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 6: Now conductor rotates to position 6.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

Position 7: Now conductor rotates to position 7.At this point velocity vector V is parallel to magnetic flux lines of poles.So at this position conductors do not cut the flux lines, there will not be change in flux so emf induced inside the conductor is zero.

Position 8: Now conductor rotates to position 8.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be maximum amount of change in flux so emf induced is maximum at this point.

So for one complete rotation of a conductor i.e, 360 degrees there will be four maximum positions of emf this is indicated in the following figure.
°


Induced emf inside the alternator is sinusoidal in nature.Four maximum peaks is 720 degrees.Conductor rotation angle is mechanical degree and emf wave cycle degree for one complete rotation of conductor gives electrical degree.

Here mechanical degree is 360 degrees and electrical degree is 720 degrees.  Since for one complete rotation of conductor two complete emf cycles are produced.

This says that electrical degree depends on number poles inside the alternator. Now we can obtain relation between mechanical degree and electrical degree as

360° mechanical = 360° ✕ P/2 electrical

P = number of poles

1° mechanical = (P/2)° electrical.

In this post we have discussed about difference between mechanical degree and electrical degree.
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Generation of electrical energy

GENERATION OF ELECTRICAL ENERGY


Energy exists in different forms in nature but the most important form is the electrical energy.Now a days usage of electricity is very high it has become a basic need for everyone. 

Why electrical energy why not other energy sources?

Well, the simple answer to this is the modern technology has developed in such a way that electrical energy can be easily converted into all other energy forms. It also has other advantages  as mentioned below.

1.Greater flexibility: As it can be easily transported with the help of conductors from one place to other it has great flexibility.

2.Convenient : As it can be easily converted into other forms of energy it is very convenient form.  If we take the example of converting electrical energy into heat energy  all we need to do is just pass electricity through a resistor then electrical energy converts o heat energy. Similarly, all the others forms of energy like light,mechanical etc can be obtained easily from electrical energy.

3.Cheapness: When compared to other forms of energy electrical energy is much cheaper . Thus it is  economical to use for any purpose.

4.Cleanliness: Electrical energy doesn't produce  smoke,ash or poisonous  gases. So it maintains cleanliness.

5.Easy control: The electrically operated machines can be controlled easily by switching on or off the switch. For example we can turn off or on the fan by switching off or switching on the switch. And speed can also be easily controlled for example speed of fan can be adjusted by using a regulator. So it is easy to control.

6.High transmission efficiency:  Consumers of electrical energy are located away from the electricity generation stations generally.But with the help of over head line conductors and by using transformers and few other equipment's electricity can be supplied efficiently with less amount of losses.

The above mentioned advantages made usage of electrical energy popular than other energy forms.

Generation of electrical energy:

Converting  different forms of energy that are present in nature into electrical energy is known as generation of electrical energy.

To get the basic idea of generation of electrical energy observe the following figure. 


Energy from any of the sources like heat, wind, hydro, fossil etc can be given as input to the prime mover. For example take hydro energy, Water at certain head  when falls on the prime mover which is a rotating part rotates the prime mover in this way the potential energy exerted on it is converted to mechanical energy. This prime mover drives generator and the generator converts mechanical energy to electrical energy.

Sources of energy:

1. Fuels: Fuels like  coal,  oil and natural gas are the main sources of energy. The heat energy produced  by these fuels is converted into mechanical energy by certain type of  prime movers like steam engines, steam turbines etc. The prime mover drives the alternator which converts mechanical energy into electrical energy. Although these fuels play main role in the electrical energy production now a days we need to see other alternatives as there quantity is diminishing due to increase in the usage of electrical energy. The alternative to them is renewable energy sources likes solar, wind, hydel.


2.Solar energy:  Sun is the major source of energy. Electrical energy can be produced from sun by focusing the heat energy produced  by sun on reflectors and heating water which produces steam which in turn rotates the turbine which is coupled to the generator and this generator converts mechanical energy to electrical energy. As it has limitations like availability of solar energy is not possible all the time it can be used as alternative wherever other sources of energy are not available abundantly.


3.Water:  When water present at certain head falls down on turbine the potential energy possessed by water is converted into mechanical energy by a water turbine. This turbine drives the generator which converts mechanical energy to electrical energy.



4. Wind: To generate electrical energy from wind energy a wind mill is established. This runs the generator which produces electrical energy. Wind mills are generally placed at hilly areas.It is cheaper way to generate electrical energy.

5.Nuclear energy: Very large amount of heat can produced by nuclear fuels like uranium. This heat energy is utilized to produce steam. This stem rotates the steam turbine and runs the generator which can produce electrical energy.



This helps you to understand the basics of generation of electrical energy from different power plants.  

Efficiency:

Some energy is lost i.e converted to other form of energy other than electrical energy  while converting any input energy to output electrical energy. Efficiency gives you how efficiently the input energy given is converted to output electrical energy. Efficiency is generally calculated in percentage.

Efficiency of power plant =  output energy / input energy = output power / input power.
Power is rate of flow of energy.

In this post we have learnt about electrical energy importance and generation of electrical energy from different power plants.

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