TRANSFORMER AND ITS TYPES

TRANSFORMER PRINCIPLE AND TYPES OF TRANSFORMER

FLEMING RIGHT HAND AND LEFT HAND RULES

Fleming Left Hand rule and Fleming Right Hand rule

Whenever a current carrying conductor comes under a magnetic field, there will be force acting on the conductor and on the other hand, if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor. In both of the phenomenons, there is a relation between magnetic field, current and force. This relation is directionally determined by Fleming Left Hand rule and Fleming Right Hand rule respectively. 'Directionally' means these rules do not show the magnitude but show the direction of any of the three parameters (magnetic field, current, force) if the direction of other two are known. Fleming Left Hand rule is mainly applicable for electric motor and Fleming Right Hand rule is mainly applicable for electric generator. In late 19^th century, John Ambrose Fleming introduced both these rules and as per his name, the rules are well known as Fleming left and right hand rule.

Fleming Left Hand Rule

It is found that whenever an current carrying conductor is placed inside a magnetic field, a force acts on the conductor, in a direction perpendicular to both the directions of the current and the magnetic field. In the figure it is shown that, a portion of a conductor of length L placed vertically in a uniform horizontal magnetic field strength H, produced by two magnetic poles N and S. If i is the current flowing through this conductor, the magnitude of the force acts on the conductor is,

F = BiL

Hold out your left hand with forefinger, second finger and thumb at right angle to one another. If the fore finger represents the direction of the field and the second finger that of the current, then thumb gives the direction of the force.

While current flows through a conductor, one magnetic field is induced around it. This can be imagined by considering numbers of closed magnetic lines of force around the conductor. The direction of magnetic lines of force can be determined by Maxwell's corkscrew rule or right-hand grip rule. As per these rules, the direction of the magnetic lines of force (or flux lines) is clockwise if the current is flowing away from the viewer, that is if the direction of current through the conductor is inward from the reference plane as shown in the figure.

Now if a horizontal magnetic field is applied externally to the conductor, these two magnetic fields i.e. field around the conductor due to current through it and the externally applied field will interact with each other. We observe in the picture, that the magnetic lines of force of external magnetic field are from N to S pole that is from left to right. The magnetic lines of force of external magnetic field and magnetic lines of force due to current in the conductor are in same direction above the conductor, and they are in opposite direction below the conductor. Hence there will be larger numbers of co-directional magnetic lines of force above the conductor than that of below the conductor. Consequently, there will be a larger concentration of magnetic lines of force in a small space above the conductor. As magnetic lines of force are no longer straight lines, they are under tension like stretched rubber bands. As a result, there will be a force which will tend to move the conductor from more concentrated magnetic field to less concentrated magnetic field, that is from present position to downwards. Now if you observe the direction of current, force and magnetic field in the above explanation, you will find that the directions are according to the Fleming left hand rule.

Fleming Right Hand Rule

As per Faraday's law of electromagnetic induction, whenever a conductor moves inside a magnetic field, there will be an induced current in it. If this conductor gets forcefully moved inside the magnetic field, there will be a relation between the direction of applied force, magnetic field and the current. This relation among these three directions is determined by Fleming Right Hand rule

This rule states "Hold out the right hand with the first finger, second finger and thumb at right angle to each other. If forefinger represents the direction of the line of force, the thumb points in the direction of motion or applied force, then second finger points in the direction of the induced current.

LAWS OF THERMODYNAMICS

Basic Law of Conservation and First Law of Thermodynamics

OBJECTIVES The objective is to determine the basics understanding of following concepts:

1. Law of Conservation of Mass
2. Law of Conservation of Energy
3. Co-relation between Mass and Energy
4. Co-relation between Energy and Work
5. Concept about Total Energy
6. First Law of Thermodynamics

Law of Conservation of Mass

This law states that mass is non destructible or it can not be created or destroyed. According to this law, there exits a relationship for mass flow at different sections in a stream of flow. In the given below fig, flow passing through a pipe is given by: Steady-state-flow condition for above equation is
A₁.V₁. ρ₁           A₂.V₂. ρ₂ Above equation is the result of law of mass conservation and is a one dimensional equation.

Law of Conservation of Energy

As per this law “energy neither be destroyed nor be created”. Conversion of energy from ‘one form to another’ took place, whenever system changes its state.

Eaxmples : in applications like: - Potential energy (PE) changes to Kinetic energy (KE) during flow of water through pipe. - Automobile K.E changes to heat energy during breaking of automobile on account of friction. - Conversion of Electrical energy to heat, in the event of current flow through a resistor. Thus in any process, energy only changes its from and thus will not change the total energy of the system and the surrounding (means universe).

Relation between Mass and Energy

As per Einstein’s theory of relativity about mass and energy; it is clear that Mass and Energy are convertible.

RELATION BETWEEN -ENERGY AND WORK

Newton’s second law of motion provides the concept of Work, KE and PE Assume, if the body moves then its initial and final position and velocity shall be respectively s₁, s₂ and V₁, V₂ because of the involvement of force component F. From Newton’s second law of motion the magnitude of the force component (F_s) is associated with change in magnitude of V by Above Eq can be re-arranged as In the above ds/dt is velocity (V) and integrating the equation for initial and final position ( s₁ and s₂) Integrating the above equation on both gives Left-side of the above equation can be equated to The Quantity is the Kinetic Energy (KE) of the body and is a scalar quantity & extensive property and change in Kinetic energy is given by Unit of KE and work are same i.e N-m or J or KJ

Similarly gravitational Potential Energy(PE) of the body is mgh and is a scalar quantity and change in Potential energy is given by It is a extensive property. Unit of PE is same as that of work i.e N-m or J or KJ. Where h is the elevation of the body with respect to earth surface.

Product of -force (F) and displacement(ds) is known as work and also be equated to change in Kinetic Energy of the body. Unit is N-m. Power(P) is rate of transfer of energy by work and can be equated Force(F) X velocity(V). OR Rate-of-doing work.

Total Energy Concept

Total-Energy of the system engulf Kinetic Energy (KE), Potential Energy (PE) and miscellaneous energy. Examples are given as:

1. when the spring is compressed. In this case energy is stored within the spring.
2. Increase in stored energy is the example of total-energy during battery charging processes.

In above examples the change in system-energy is not on account of changes in kinetic or potential energy but on account of change in internal-energy(U). When the process changes then its Internal energy is given by U₂ – U₁ and specific-internal energy is represented by u expressed on a unit-mass basis. Total-Energy change is given by:

Energy Transfer by Heat

So far we have discussed only those interactions between system and surrounding that are related with work. But it is also possible for a closed system to interact with the surrounding that can’t be called as work.

Example : when gas come in contact with the hot surface of a plate in a cylinder, then gas energy increases although no work has performed. This process is called energy transfer by heat. (Q) is the amount of energy transferred across the boundary of a system. Then Q into a system is considered as positive, while Q out of the system is considered as negative. Q > 0 (considered as positive) ⇒ Heat transfer to the system Q < 0 (considered as negative) ⇒ Heat transfer from the system

The heat-transfer not just depends on the end-state, but depends on the particular process. Similarly heat also not depends on the end-state. The value of heat-transfer (Q) depends on the specific process and not just on just end states. The amount of energy transfer by heat in a process is given by integral of: Where limits means from state 1 to state 2 and do not refer to the values of heat at those states. The sign notation used for heat transfer (Q) is opposite to that of work transfer (W). A Positive value of work (W) implies transfer of energy from system to surroundings and vice versa.

First Law of Thermodynamics or Energy Balance IN a Closed System

Transfer of energy by work (W) or by heat (Q) is the only way by which energy with in the closed system can be changed. Under lined principle is Energy is Conserved. When energy (heat and work) crosses the boundary in a system, then Internal-energy (U) of the system get change and this phenomenon is called First law of Thermodynamics. [Energy Change with in the system during some time interval] = [Net energy transferred in the system boundary by heat transfer process during the same interval] - [Net energy transferred out of the system boundary by work during the same interval]

In the above equation the system energy increases or decreases by an amount equal to the net-energy transferred across the boundary and can be expressed as:

Total Energy (E2 – E1) or Δ E	Q - W
Δ KE + Δ PE + Δ U	Q - W
Energy balance in differential form (dE) Where dE is property	δQ – δW heat and work are not property
dE/dt	[δQ /dt – δW/dt]

In above equation energy transfer across boundary results in change in one or more macroscopic form of energy like KE, PE and Internal energy(U) Energy balance with respect to time is expressed as: [Time rate of change of energy contained with in the system at time t] =[Net rate at which energy is being transferred in through heat transfer at time t] - [Net rate at which energy is being transferred out through work at time t] Since the time rate of change of energy is given by, Therefore,

dE/dt	[δQ /dt – δW/dt]
[dKE/dt + dPE/dt + dU/dt]	[δQ /dt – δW/dt]

Ohms Law | Equation Formula and Limitation of Ohms Law

PPT ON POWER ELECTRONICS

PPT ON POWER ELECTRONICS

PPT ON ELECTRICAL MACHINES

Electrical Machines PPT

Joules Law of Heating

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We know about the heating effect of current, when it flows through a circuit due to collision between electrons and atoms of wire. But precisely how much heat is generated during current flow through a wire, on what conditions and parameters does it depend?

How can we know about this? To solve this problem, Joule coined a formula which explains this phenomenon accurately. This is known as Joule’s law. This law is explained in detail afterwards.

Joule’s Law of Heating

The heat which is produced due to the flow of current within an electric wire, is expressed in Joules. Now the mathematical representation or explanation of Joule’s law is given in the following manner.
i) The amount of heat produced in current conducting wire, is proportional to the square of the amount of current that is flowing through the circuit, when the electrical resistance of the wire and the time of current flow is constant.
i.e. H ∝ i² (When R & t are constant) ii) The amount of heat produced is proportional to the electrical resistance of the wire when the current in the circuit and the time of current flow is constant. i.e. H ∝ R (when i & t are constant)

ii) Heat generated due to the flow of current is proportional to the time of current flow, when the resistance and amount of current flow is constant.

i.e. H ∝ t (when i & R are constant) When these three conditions are merged, the resulting formula is like this -

Here ‘H’ is the heat generated in Joules, ‘i’ is the current flowing through the circuit in ampere and ‘t’ is in seconds. When any three of these are known the other one can be equated out. Here, 'J' is a constant, known as Joule's mechanical equivalent of heat. Mechanical equivalent of heat may be defined as the number of work units which, when completely converted into heat, furnishes one unit of heat. Obviously the value of J will depend on the choice of units for work and heat. It has been found that J = 4.2 joules/cal (1 joule = 10⁷ ergs) = 1400 ft. lbs./CHU = 778 ft. lbs/B Th U It should be noted that the above values are not very accurate but are good enough for general work.

Now according to Joule's law I²Rt = work done in joules electrically when I ampere of current are maintained through a resistor of R ohms for t second. By eliminating I and R in turn in the above expression with the help of Ohm’s law , we get alternative forms as

LENZ LAW

Lenz Law of Electromagnetic Induction

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Lenz's law is named after the German scientist H. F. E. Lenz in 1834. Lenz's law obeys Newton's third law of motion (i.e to every action there is always an equal and opposite reaction) and the conservation of energy (i.e energy may neither be created nor destroyed and therefore the sum of all the energies in the system is a constant).

Lenz law is based on Faraday's law of induction, so before understanding Lenz's law; one should know what is Faraday’s law of induction? When a changing magnetic field is linked with a coil, an emf is induced in it. This change in magnetic field may be caused by changing the magnetic field strength by moving a magnet towards or away from the coil, or moving the coil into or out of the magnetic field as desired. Or in simple words, we can say that the magnitude of the emf induced in the circuit is proportional to the rate of change of flux.

Lenz's Law

Lenz's law states that when an emf is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced emf is such, that it produces an current that's magnetic field opposes the change which produces it.

The negative sign used in Faraday's law of electromagnetic induction, indicates that the induced emf ( ε ) and the change in magnetic flux ( δΦ_B ) have opposite signs. Where ε = Induced emf δΦ_B = change in magnetic flux N = No of turns in coil

Reason for Opposing, Cause of Induced Current in Lenz's Law?

• As stated above, Lenz's law obeys the law of conservation of energy and if the direction of the magnetic field that creates the current and the magnetic field of the current in a conductor are in same direction, then these two magnetic fields would add up and produce the current of twice the magnitude and this would in turn create more magnetic field, which will cause more current and this process continuing on and on leads to violation of the law of conservation of energy.

• If the induced current creates a magnetic field which is equal and opposite to the direction of magnetic field that creates it, then only it can resist the change in the magnetic field in the area, which is in accordance to the Newton's third law of motion.

Explanation of Lenz's Law

For understanding Lenz's law, consider two cases : CASE-I When a magnet is moving towards the coil.

When the north pole of the magnet is approaching towards the coil, the magnetic flux linking to the coil increases. According to Faraday's law of electromagnetic induction, when there is change in flux, an emf and hence current is induced in the coil and this current will create its own magnetic field . Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the increase in flux through the coil and this is possible only if approaching coil side attains north polarity, as we know similar poles repel each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in anticlockwise direction.

CASE-II When a magnet is moving away from the coil

When the north pole of the magnet is moving away from the coil, the magnetic flux linking to the coil decreases. According to Faraday's law of electromagnetic induction, an emf and hence current is induced in the coil and this current will create its own magnetic field . Now according to Lenz's law, this magnetic field created will oppose its own or we can say opposes the decrease in flux through the coil and this is possible only if approaching coil side attains south polarity, as we know dissimilar poles attract each other. Once we know the magnetic polarity of the coil side, we can easily determine the direction of the induced current by applying right hand rule. In this case, the current flows in clockwise direction.

NOTE : For finding the directions of magnetic field or current, use right hand thumb rule i.e if the fingers of the right hand are placed around the wire so that the thumb points in the direction of current flow, then the curling of fingers will show the direction of the magnetic field produced by the wire. The Lenz law can be summarized as under:

• If the magnetic flux Ф linking a coil increases, the direction of current in the coil will be such that it will oppose the increase in flux and hence the induced current will produce its flux in a direction as shown below (using right hand thumb rule). • If magnetic flux Ф linking a coil is decreasing, the flux produced by the current in the coil is such, that it will aid the main flux and hence the direction of current is as shown below,

Application of Lenz's Law

• Lenz's law can be used to understand the concept of stored magnetic energy in an inductor. When a source of emf is connected across an inductor, a current starts flowing through it. The back emf will oppose this increase in current through the inductor. In order to establish the flow of current, the external source of emf has to do some work to overcome this opposition. This work can be done by the emf is stored in the inductor and it can be recovered after removing the external source of emf from the circuit

• This law indicates that the induced emf and the change in flux have opposite signs which provide a physical interpretation of the choice of sign in Faraday's law of induction.

• Lenz's law is also applied to electric generators. When an current is induced in a generator, the direction of this induced current is such that it opposes and causes rotation of generator (as in accordance to Lenz's law) and hence the generator requires more mechanical energy. It also provides back emf in case of electric motors.

• Lenz’s law is also used in electromagnetic braking and induction cook tops.

Ohms Law | Equation Formula and Limitation of Ohms Law