Tuesday, 27 February 2018

All About Detail Of Ideal Transformers And Auto Transformers !!

All About Detail Of Ideal Transformers And Auto Transformers !!



Detail About Ideal Transformer 




An Ideal Transformer is one which has no losses and magnetic leakage.






An Ideal Transformer has no ohmic resistance in the windings and no leakage flux. 


  • Efficiency will be 100 and voltage regulation is zero.

 In other words, an Ideal Transformer consists of two purly inductive coils wound on a loss-free core. But in actual practice, it is impossible to obtain such an ideal transformer.

Question part on ideal transformer :

1) state the ideal transformer??? 
Ans:An ideal transformer is one which has no losses and magnetic leakage. An ideal transformer has no ohmic resistance in the windings and no leakage flux. 

2)what is efficiency of ideal transformer??? 
Ans:100%

3)how many voltage regulation in Ideal transformer?? 
Ans:Zero

4)the ideal transformer consists two purly ______   coil?? 
Ans: inductive


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Detail About Auto Transformers 


Description 



The Auto Auto-transformer works on the principle of self induction.The auto- transformer differs from a two winding transformer in a way in which the primary and secondary are inter-related.

An auto-transformer is special Type Of Transformer having a single winding of insulated copper wire such that the part of the winding is common to the Primary And Secondary i e. that serves as both primary and secondary


(A) 

In Auto-Transformer, the single winding of an insulated copper wire is wound on a laminated core of slicon steel and therefore both primary and secondary sections of this winding are on the same Magnetic Circuit. An auto-transformer may step-up or step down the voltage.

(B) 

and (b) shows the step down and step-up auto-transformers respectively Referring Fig. (a), one end of the winding (C) is Common To Primary as well as secondary, while other two ends A and B form the other terminals of primary and secondary
respectively. Thus AC forms the primary winding with N1 turns and BC forms the Secondary Winding with N2 turns. As N2 N1, the secondary voltage V2 vi and therefore it acts as a step down auto-transformer Referring to fig. (b),


the whole winding (AC) acts as while the part of the winding is common to both primary and secondary Thus forms Secondary Winding with N2 turns and BC forms the primary winding with NI turns. As N2 N, the secondary voltage Va Vi and therefore it acts as a step up auto-transformer. Under ideal conditions (An auto-transformer which has no losses and magnetic leakage), the transformation ratio of an Auto-Transformer given by

k=(V2/V1)=(N2/N1)=(I1/I2)
If k>1 then the auto transformer is called step-up and if k<1 then the auto transformer is called step down.

Question part of auto transformer  :

1) The Auto Auto-transformer works on the principle of ______???
Ans: self induction

2) in the auto transformer how many winding???
Ans: one

3)what is the transformation ratio of an auto-transformer ????
Ans: k=(V2/V1)=(N2/N1)=(I1/I2)



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Saturday, 24 February 2018

Do You Know How Manny Types Of Transformer???

Basic Theory On Electrical Transformer And All Types Of Electrical Transformers!! 



Different Types Of Transformers And Detail Of The Electrical Transformer 






According To Construction, there are two main types of transformers namely

  1. (i) Core type and 
  2. (ii) Shell type




 Core type transformers


  • In this Type of Transformer, the windings surround the iron core. 
  • Both windings are divided and half of each winding is placed on each as shown in figer so that the two windings can be closely coupled together to keep the leakage flux and hence leakage reactance low.


The Low Voltage (l.v.) winding is wound on the inside nearer to the core while the high voltage (h.v.) winding is wound over the l.v. winding away from the core in order to reduce the amount of Insulating Materials required and also the insulation of low voltage winding is easy.


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With this Arrangement Of Windings, only one layer of high voltage insulation is required and removal or repair of the high voltage winding, which is more liable to faults than the low Voltage Winding, is easy and convenient.


Small transformers have core of square or Rectangular Cross-Section but for large size transformers stepped or cruciform core is used as shown in figer. The core section for core type of transformers may be square, rectangular or stepped. Shall Type Transformers use cores with rectangular cross-section.


As the space utilization is better with stepped cores, the length of mean turn of copper is reduced and therefore Copper Losses and cost of copper also reduced.

Shell type transformers 

In Shell Type Transformers, the windings are put around the central limb and the flux path is completed through two side limbs as shown in figer .


The Central Limb Carries total mutual flux while the side limbs forming a part of a parallel magnetic circuit carry half the total flux.

Consequently, the cross-sectional area and hence width of the central limb is twice that of each of the side limbs. The sandwich type of winding is used in which the sections of the primary winding are sand wiched in between the sections of the secondary winding as shown in figer .

therefore the Leakage Flux is reduced and hence leakage reactance will be low. To minimize the amount of high voltage insulation, low voltage coils are placed adjacent to the Iron Core.


 In this Type Of Transformer, the coils are better braced mechanically that they are less easily displaced by the high electro-mechanical forces that frequently develop during short circuits

Question part about the types of transformers :

1)give a type of transformer according to construction?????
Ans: (i) Core type and (ii) Shell type

2)in core type transformer winding on ____??
Ans:the windings surround the iron core.

3) give one advantage of core type transformer??? 
Ans:As the space utilization is better with stepped cores, the length of mean turn of copper is reduced and therefore copper losses and cost of copper also reduced.

4)how arrange shell type transformer winding????? 
Ans:In shell type transformers, the windings are put around the central limb and the flux path is completed through two side limbs.

5)give one advantage of shell type transformer???
Ans: In this type of transformer, the coils are better braced mechanically that they are less easily displaced by the high electro-mechanical forces that frequently develop during short circuits




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Wednesday, 21 February 2018

What is Working Principle Of Electrical Transformer???

Basic Of Electrical Transformer, And How Working Process Of  Electrical Transformer 



All About Electrical Transformer And Its Basic Knowledge And Basic Principle 






  • A transformer is a statie Electromagnetic Device consisting of two or more windings which link with a common magnetic field.
  • A transformer a device that Transfers Electric Power from one circuit to another without a change of frequency. 
  • It can raise or lower the voltage in a circuit but with a Corresponding Decrease or increase current 
In brief, a transformer in is an ac machine that





  • -> Transfers Electrical Energy from one circuit to another
  • ->does so without a Change Of Frequency
  • ->does so by the principle of Electro-magnetic Induction
  • ->has electric eircuits that are linked by a Common Magnetic Circuit.


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Since the basic Construction Of Transformer requires no moving part, requires minimum amount of repair and maintenance. The ene transfer usually takes place with a change of voltage, although this not always necessary.

When the transformer raises the voltage i e. when the output voltage of a transformer is higher than its input voltage, it is called the step- up and when it lowers the voltage, it is called the step-down transformer

A Simple Transformer consists of a ferromagnetic core or silicon steel core and two windings placed on it.
  •  The windings are electrically separated but magnetically linked through a path of low reluctance as shown in figer
  •  The windings are insulated from both the core and each other.
  •  The core is made of thin silicon steel laminations to provide nce to the magnetic flux. 
  • The winding connec to the supply mains is called the primary and the winding connected
To the load circuit is called the secondary. In other words, the winding In to the load from which drawn out is called Secondary Winding.

A transformer work on the principle of electromagnetic induction . I.e. mutual induction between two circuits linked by a Common Magnetic Flux .

When the primary winding is connected to an ac supply mains, a current flows through it. An alternating flux is set in the laminated core which links with the secondary winding and produces mutually induced emf in the secondary winding according to Faraday's laws of electromagnetic induction,

 e= M (dI/dt).

the secondary circuit is closed a current flows in it and therefore electrical energy is transferred from primary the secondary winding.

Question Parts On The Electrical Transformers :

1)Define the transformer??? 
Ans:A transformer is a statie electromagnetic device consisting of two or more windings which link with a common magnetic field.
  • A transformer a device that transfers electric power from one circuit to another without a change of frequency. 
  • It can raise or lower the voltage in a circuit but with a corresponding decrease or increase current 
2)when the output voltage of a transformer is higher than its input voltage, it is called _____???
Ans: step-up transformer

3) what is work of transformer?? 
Ans:transfers electrical energy from one circuit to another 
->does so without a change of frequency
->does so by the principle of electro-magnetic induction
->has electric eircuits that are linked by a common magnetic circuit.

4)the winding In to the load from which drawn out is called which winding???
Ans:secondary-winding

5)A transformer work on the which  principle???
Ans:electromagnetic induction


Challenging Example For Electrical Engineer

Ex :  A Transformer Have 500 turnes Of Primary Winding  And 10 Turnes Of Secondary Winding Than Determine The Current In Primary And Secondary Winding?? Given there the secondary winding connected with 15ohm resistance Load!! 

Hint : I2=V2/R

Comment Your Answer In Comments Box!! 



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Sunday, 18 February 2018

Widely used Application In The Work For Starting Of Motor!!??

In Real Life Widely  Useful Application Is Three Phase Starter,  How Its Work And How Its Really  Operating In Real Life




Function Of Starter,  Working Principle Of Starter And Full Detail About The Three Phase Starter.



Function of starter 


The device which is used to start the d.c. motor is called a Starter .The function of the starter is to limit the starting high current to a safe value.






NECESITY OF A STARTER


EMF equation for Armature Circuit
E =V - IR


The current drawn by a Motor Armature is
I=(V - E) /R


In case of d.c. motor the back emf develop is directly proportional to the speed because
E =(§ZNP) /(60A)






When the motor is at reast the speed of the motor is zero hence back emf Eb will be zero so if a d.c.

motor is connected directly to the supply main it will drawn a very Large Current.


The current drawn by the aature becomes
I=V/R




  • The resistance of the Armature Winding r, is very small (hardly 1 to 2 ohm), as such the current flowing in the armature winding under starting condition becomes quite large. 
  • The Starting Current may be 5 to 7 times that of full load current. 
  • The Starting Current drawn by the de motor can be limited to safe value either by using a starter or by inserting a variable rheostat in series with the armature circuit as shown in Figer.

  •  The Starter is used only for the short duration (5 to 10 sec) which limits the starting high current to a safe value.


Very small d c. motors may be started directly from the supply lines because of the follawing reasons


(1) Relatively higher armature resistance R compared to large motors and
(2) Law moment of intertia.
The dc shunt ar compound motor is started by the following two types af starters:
(1)Three pointt starter and
(2)Four paint starter


in figer shows a wiring diagram of a d c. three point starter.

It consists graded starting resistances, rs which is connected in series with armature, two protective devices namely no volt and overload release, starting arm and the brass arc segment s.




Generally three terminals of the Starter L F and A are brought out, which are connected to the positive line terminal, shunt field and armature terminal of the motor respectively.

  • For starting the motor, the dc supply is switched on by closing the switch and then the starting arm is slowly moved to the right (clockwise). 
  • As soon as the suarting arm makes contact with stud and brass are segment s, whole of the starting resistance r.
  •  inserted in series with the armature and at the same time the circuit is directly connected across the supply through the segment s and the holding coil (NVC) is also energized.

Therefore the current drawn by the armature at this instant will be
I=V/(Ra+Rs)


As the Starting Arm is further moved, the starting resistance r, gradually cut out and when the arm reaches the RUN position, the entire starting resistance is cut out. No volt and overload release coils are the protective devices provided in the starter.


Questions  Related To Three Phase Starter :

1) give thr Function of starter ???
Ans:The device which is used to start the d.c. motor is called a starter.
The function of the starter is to limit the starting high current to a safe value.


2)When the motor is at reast the speed of the motor is zero hence back emf Eb will be ________????
Ans: zero


3)The starting current may be _______ that of full load current. ??
Ans:5 to 7 times


4)The dc shunt and compound motor is started by the how many types af starters and which????? 
Ans : Two
(1)Three pointt starter and
(2)Four paint starter


5) The starter is used only for the short duration ______ time which limits the starting high current to a safe value.???
Ans:the short duration.



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Thursday, 15 February 2018

How We Can Speed Control Of Electrical Machine!!

How We Can Speed Control Of Electrical Machine!! 



One Of The Most Useful Method For Speed Control Is Given As Below In Article




It is an application of the Method Of Speed Control by the use of variable voltages to the armature of the motor whose speed controlls required.




 Fig  shows the sehematie diagram of the ward Leonard method or speed of a dc shunt motor.


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  • The Speed Control Of DC Motor by means of an adjustable voltage generator connected across the armature dc motor terminals of the called Ward Leonard Method. 
  • As shown in figer M1 is the main dc motor whose speed is to be controlled, G is separately excited de generator which can be driven either by a constant speed 3 phase AC motor (M2) or dc motor. The field winding of the main motor (M1) is Permanently Connected across the dc supply. The armature terminals of the main motor (M1) are connected directly to the armature terminals of dc generator.


@@@@@@@


In this method, a variable voltage is applied to the Armature Of Main Motor (M1) for controlling the speed.


This variable voltage is obtained a Motor-Generator set (M-G set). The variable voltage of the generator can be obtained by varying resistance (field current) in its field circuit.


Thus, the applied voltage to the main motor can be changed from zero to maximum value and hence any Desired Speed the main motor can be obtained.

This method of Speed Control is most effectively used, where a wide very sensitive type of speed control is needed, such as in paper mills, elevators etc.

Advantages


  • (1)very fine speed control over the whole range from zero to normal rated speed in both directions can be obtained.
  • (2)Uniform acceleration can be obtained.
  • (3)Good speed regulation


Disadvantages


  • (1)This arrangement is costly due to two extra machines.
  • (2)overall efficiency of the system is low.


Question part Of This Article :

(1)give one example  an application of the method of speed control by the use of variable voltages to the armature of the motor whose speed controlls required.???
Ans: ward Leonard method

(2)what is ward Leonard method??? 
Ans:The speed control of dc motor by means of an adjustable voltage generator connected across the armature dc motor terminals of the called Ward Leonard method.

(3) give advantage of ward Leonard method??
Ans:(1)very fine speed control over the whole range from zero to normal rated speed in both directions can be obtained.
(2)Uniform acceleration can be obtained. (3)Good speed regulation

(4) list the disadvantages of ward Leonard method??? 
Ans:(1)This arrangement is costly due to two extra machines.
 (2)overall efficiency of the system is low.

(5)give a example where use ward Leonard method for speed controlled??? 

Ans:paper mills, elevators etc.


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Monday, 12 February 2018

What Is Back EMF Its A Useful Or Not!?

What Is Back EMF Its A Useful Or Not!? 




All About Back EMF



when the armature of a dc motor rotates, in a Magnetic Field, its conductors cut the magnetic flux.




Therefore an emf is induced in them according to Faraday's laws of Electromagnetic Induction, whose direction is in opposition to the applied voltage (V)  as shown in figer.



Because of its opposing direction, it is called counter e.m.f or Back EMF (Eb).





when the armature of a dc motor rotates, an e mf is induced in armature conductors which opposes the applied voltage is known as back em f or counter e.m.f Its value is always less than the applied voltage.

Its value is the same as for the motionally induced Back EMF in the dc generator,

i.e. Eb = (§ZNP)/(60A)



The applied voltage (V) has to force current through the armature conductors against this Back EMF The electric workdone in overcoming this opposition is converted into mechanical energy developed in the armature.

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  • Energy conversion is not possible unless there is some opposition.
  • In dc generators, the opposition is provided by magnetic force and in dc motors, Back EMF does this job.


Question part about Back EMF:

1)when the armature of a dc motor rotates, in a magnetic field, its conductors cut the magnetic flux Therefore an emf is induced in them according to _______law?????
Ans:Faraday's laws of Electromagnetic induction,

2) what is the job of back emf in dc generator??? 
Ans:In dc generators, the opposition is provided by magnetic force and in dc motors, back e m f does this job.

Friday, 9 February 2018

Different Types Of Losses In The DC Machine And Their Effect On The Machine! !

Different Types Of Losses In The DC Machine And Their Effect On The Machine! !



Description About The All Different Types Of Losses Which Occur In DC Machine And Their Details .





The Losses Occurring In DC Machines can be listed as below:
(1) copper losses
(2) Magnetic or iron losses
(3) Mechanical losses
(4) Stray load losses


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(i) Copper losses

These losses occur in those parts of de machines which carry electric current Copper losses occur due to the current flowing in Various Windings of the machine.

These losses are directly proportional to the square of current nowing in the winding and the ohmic resistance the winding .

The various copper losses occurring in the windings are





  • (A)  Armature copper loss
  • (B) Shunt field copper loss
  • (C) Series field copper loss
  •  (D) Copper loss in interpole winding
  • (E) Brush contact loss


Shunt field copper loss is constant for shunt and compound wound dc machines. All other copper losses (Armature circuit losses) are called variable losses because these are directly proportional  to the square of armature current which varies with the load.

The Armature Copper Loss is about 30-40% of totle full load losses amd field copper losses are about 20-30%of full load losses.




(ii)  Magnetic losses

These losses are also called iron loss or core loss.
These losses occur in Armature Core And Teeth where the iflux is changing.
Iron losse consists of (1) Hysterisis losses and (2) Eddy current losse.

Since field is constant and dc machines are usually operated at constant speed, these losse are almost constant. These are about 20% to 30%of full load losses.

(a)  Hysterisis losses



This loss is due to reversal of Magnetism Of The Armature Core.
These losses pccur in armature core teeth of the dc machine.
Hysteresis Losses can be reduced by using core material of silicon steel which has low hysterisis coefficient.

(b) Eddy current loss

When Armature Core Rotates in magnetic field of poles it also cuts the magnetic flux. Hence an emf is induce in the body of the core according to the low of electromagnetic induction. This emf set up current in the body of the armature core and its know as eddy current.
To Minimize Eddy Current losses the armature core is made of thin laminated stamping. The thickness of laminating used for armature core is 0.35 to 0.5 mm.

(iii) Mechanical losse

Due to friction of bearing air friction or windage losses in dc machins. These are known as Mechanical Losses.

  • (a)  Bearing and brush friction losses
  • (b)  Winding loss or air friction of rotating armature.

These losses are about 10-20% of totle full load losses.

(iv)  stray losses

There are certain type of losses which can not be easily determined  .
They appear when machine is loaded. These inderminanble losses are called Stray Losses and are due to the following reasons. 

  • (1)Distortion of flux because of armature reaction
  • (2)due to eddy current in conductore
  • (3)short circuit current in the armature coil undergoing commutation.

Stray Losses may be assumed 0.5-1%of the power output for machine.

Questions Related To This Topic:

1)list The losses occurring in dc machines ???
Ans: listed as below:
(1) copper losses
(2) Magnetic or iron losses
(3) Mechanical losses
(4) Stray load losses

2) give The various copper losses occurring in the windings ??????
Ans:
(A)  Armature copper loss
(B) Shunt field copper loss
(C) Series field copper loss
 (D) Copper loss in interpole winding
 (E) Brush contact loss

3)The armature copper loss is about ______% of totle full load losses amd field copper losses are about ______%of full load losses.???
Ans:30-40 and  20-30

4)Magnetic losses is also known as???? 
Ans:These losses are also called iron loss or core loss.

5)magnetic loss consist which losses???
Ans:Iron losse consists of (1) Hysterisis losses and (2) Eddy current losse.

6)magnetic loss  are about _____of full load losses.???
Ans: 20% to 30%

7)explain hysteresis losses in dc machine??? 
Ans:Hysterisis losses

This loss is due to reversal of magnetism of the armature core.
These losses pccur in armature core teeth of the dc machine.
Hysteresis losses can be reduced by using core material of silicon steel which has low hysterisis coefficient.

8)define eddy current??? 
Ans:When armature core rotates in magnetic field of poles it also cuts the magnetic flux. Hence an emf is induce in the body of the core according to the low of electromagnetic induction. This emf set up current in the body of the armature core and its know as eddy current

9)mechanical losses consists which losses??? 
Ans:(a)  Bearing and brush friction losses
(b)  Winding loss or air friction of rotating armature.
These losses are about 10-20% of totle full load losses.

10)stray losses occurring because of??? 
Ans:(1)Distortion of flux because of armature reaction
(2)due to eddy current in conductore
(3)short circuit current in the armature coil undergoing commutation.


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Tuesday, 6 February 2018

How We Can Voltage Increase By Voltage Build Up Process And How Its Work !

How We Can Voltage Increase By Voltage Build Up Process And How Its Work ! 



Fully Describes About The Voltage Build Up Process And How Its Actually Work or How Its Helpful For The Increase Voltage

As show in figer shows the circuit diagram of a shunt generator. 




  1. Before connecting a load to a shunt generator, it is allowed to build up its voltage. 
  2. The Voltage Increasing in Voltage build-up in a self-excited dc generator depends up on the presence of a residual flux in the field poles.
  3.  Initially due to residual magnetism in the field poles, a small emf is produced. This emf circulates a small current in the field circuit, which turn produces additional flux to reinforce the original flux. 


  1. This process continues and the generator builds up the normal voltage shown in figer. 
  2. The generator excites itself due to residual magnetism and develops the voltage as described below
  3. Voltage Increase Process 

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Line OP represents the shunt field resistance.

When the generator is started a small emf (represented by OA ) is induced due to residual magnetism. 

This induced emf causes a flow of current oa' in the field circuit. This is obtained by drawing a horizontal line from point A meeting the field resistance line at point a and then from point a drawing perpendicular line meeting current axis at a' 

When field current is oa', the generated emf is a'a" which produce field current ob', which in turn produces a high voltage b' b".

 Thus it is observed that effect is cumulative and value of induced emf and field current increases until these reach point D, the point of the  intersection of the shunt field resistance line and magnetic characteristics obtain.



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Saturday, 3 February 2018

Different Types Of Magnetic Excited Systems !

Different Types Of Magnetic Excited Systems ! 



Single Excited Magnetic System 




  • Consider an attrect armature type electromagnet relay . 
  • It is Singly Excited Magnetic System. 
  • A coil of N-turnes is wound on the magnetic core connected to a voltage source (Vs). 



  • Assuming that the armature is held fixed at the position x and the current is increased from zero to some value i. 

Hence the magnetic flux will be set up in the magnetic system. The magnitude of magnetic flux dependa on M. M. F(N*i) and the reluctance of the magnetic path.




The incremental electrical energy (dWe)  due to the flow of current i in time dt is

dW=E.i dt

B-H curve for Single Excited System

For angular movements of armature  the electromagnetic torque fora linear system is given by
T=(1/2)*(i^2)*(dL/d§)
Where §=angle


Doubly Excited Magnetic System

  • Magnetic System which is excited by two independent source is called Doubly Excited Magnetic Circuit. 
  • The synchronous machines amd d.c. machines are the example of Doubly Excited Magnetic System. 
  • Doubly Excited Magnetic System which consist of stator and rotor poles and windings. 
  • The stator winding have N1 turnes is energized from source V1 and the rotor winding having N2 excited from source V2 .
  • The MMFs produced by both stator and rotor winding are in the same direction and magnetic torque Tm is in the anticlockwise direction. 

The basic principle of energy conversion

dWe = dWm + dWf

Magnetic torque developed

Tm d§ =(1/2)(i^2) dLs + (1/2)(ir^2) dLr +(is) (ir) dM
Where §=anglr
Ir= rotor current
Is= stator current




Questions Related To Different Types Of Magnetic Excited Ststem:

1)how many type for Exciting to Magnetic System??

Ans: two type (1) single excited and (2) doubly excited

2)Give the formula of  The incremental electrical energy (dWe)  due to the flow of current in the Single Excited System??
Ans: dW=E.i dt

3)Give the formula For angular movements of armature  the electromagnetic torque for a linear system ???

T=(1/2)*(i^2)*(dL/d§)
Where §=angle

4)What is Doubly Excited Magnetic System??
Ans:A magnetic system which is excited by two independent source is called doubly excited magnetic circuit.

5) Give the example of Doubly Excited Magnetic System?? 
Ans:The synchronous machines and d.c. machines .

6)Give formula for satisfied the energy conversion principle in Doubly Excited Magnetic System?? 
Ans: dWe = dWm + dWf

7)Give the formula of Magnetic torque developed in Doubly Excited Magnetic System?? 
Ans:Tm d§ =(1/2)(i^2) dLs + (1/2)(ir^2) dLr +(is) (ir) dM
Where §=anglr
Ir= rotor current
Is= stator current


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