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Resistance is defined as the property of a substance due to which it opposes the flow of Electricity i.e electrons through it. Metals, acids and salts are the good conductors of electricity. These free or loosely attached electrons (vagrant) while flowing pass through the molecules or the atoms of the conductor,collide and other atoms and electrons, thereby producing heat. The unit of Resistance The practical unit of resistance is ohm. A conductor is have a resistance of one ohm if it permits one ampere current to flow through it when one volt is applied through its terminals. The unit of resistance is ohm. Laws of Resistance  The resistance R offered by a conductor depends on the following factors: 1. It varies directly as its length l. 2. It varies inversely as the cross section A of the conductor. 3. It depends on the nature of the material. 4. It also depends on the temperature of the conductor. R= ρ.l/A where,   ρ is a constant depending o

Let n be the number of free electron available per cubic metre of the conductor material. Let v be the axial drift velocity. In time dt, distance travelled would be vdt . If A is the cross section of the conductor, then the volume is vAdt . If e is the charge of each electron  then total charge which crosses the section in time dt is dq=nAev.dt. Since current is the rate of flow of charge, it is given as i=dq/dt=(neAv.dt)/dt i=venA Current density, J=i/A=vne Ampere/m2. Normal J for copper conductor= 1.55 x 10^6 A/m2, n=10^29, e=1.6x10^-19 coulomb, v=9.7 x 10^-5 m/s = 0.58 cm/min.

The concept of Electrical grid was given by Nicole Tesla about 120 years ago. Since then the generation, transmission and distribution of Electrical energy has undergone vast changes. Giant size generators and EHV lines are very common now. The per capita consumption has increased manifold (and is still increasing) and consumers demand reliability and quality in Electric supply. The power industry is faced with challenges and opportunity of transforming the Electrical grid into smart grid to manage demand growth, conserve Energy, reduced losses, optimize efficiency, improve power quality and reliability. Smart grid also known as intelligent grid refers to combination of hardware, software and communication tools to meet the above objectives. The main features of a smart grid are: 1. It is self healing from power distuebances. 2. It ensures power quality and reliability. 3. It accommdates centralized giant size generators as well as distributed generation. 4. It uses conven

When a conductor is carrying dc current , it is uniformly distributed over the cross section of the conductor . However an alternting current flowing through the conductor does not distribute uniformly, rather it has the tendency to concetrate near the surface of the conductor. This is known as Skin effect.   Thus, skin effect is the tendency of an alternting current to concentrate near the surface of the conductor.     Due to skin effect the effective area of cross section of the conductor through which current flows is reduced consequently, the resistance of the conductor is slightly increased when carrying an alternating current. Cause of skin effect The cause of skin effect can be easily explained. A solid conductor may be thought to be consisting of a large number of strands, each carrying a small part of current. The inductance of each strand will vary according to its position. Thus, the strands near the centre are surrounded by a greater magnetic flux and hence

A black start is the process of restoring an electric power station or a part of an electric grid to operation without relying on the external transmission network. Normally, the electric power used within the plant is provided from the station's own generators. If all of the plant's main generators are shut down, station service power is provided by drawing power from the grid through the plant's transmission line. However, during a wide-area outage, off-site power supply from the grid will not be available. In the absence of grid power, a so-called black start needs to be performed to bootstrap the power grid into operation. To provide a black start, some power stations have small diesel generators, normally called the black start diesel generator (BSDG), which can be used to start larger generators (of several megawatts capacity), which in turn can be used to start the main power station generators. Generating plants using steam turbines require station service

In a conductor carrying alternating current, if currents are flowing through one or more other nearby conductors, such as within a closely wound coil of wire, the distribution of current within the first conductor will be constrained to smaller regions. The resulting current crowding is termed as the proximity effect. This crowding gives an increase in the effective resistance of the circuit, which increases with frequency. A changing magnetic field will influence the distribution of an electric current flowing within an electrical conductor, by electromagnetic induction. When an alternating current (AC) flows through an isolated conductor, it creates an associated alternating magnetic field around it. The alternating magnetic field induces eddy currents in adjacent conductors, altering the overall distribution of current flowing through them. The result is that the current is concentrated in the areas of the conductor furthest away from nearby conductors carrying curre

Constructionally, the transformers are of two general types, distinguished from each other merely by the manner in which the primary and secondary coils are placed around the laminated core. The two types are:- Core type   Shell type Another recent development is spiral core or wound core type, the trade name being spirakore transformer. Core type transformer:- In the core type transformer, the windings surround a considerable part of the core. In the simplified diagram of the core type transformer, the primary and secondary winding are shown located on the opposite limbs of the core, but in actual construction they are interleaved to reduce leakage flux. As in the figure, half the primary and half the secondary winding have been placed side by side or concentrically on each limb, not primary on one limb and the secondary on the other. The coil used are form-wound and are of the cylindrical type. In small size core type transformers, a simple rectangular core

The transformers are not connected on dc and never connected to a dc source. There will be no self emf in the primary when the transformer are connected to a dc supply. If a rated dc voltage is applied to the primary of a transformer, the flux produced in the transformer core will not vary but remain constant in magnitude and therefore no emf will be induced in the secondary winding except at the moment of switching on. Since the resistance of the primary winding is low, therefore a heavy current will flow through the Primary winding which may result in the burning out of the primary winding. This is reason that dc is never applied to a transformer. Subscribe, share and leave your comments in the comment box below. Thank you :)

An elementary transformer consists of soft iron core and two windings placed on it. The core is built up of thin soft iron or silicon steel laminations to provide low reluctance to the magnetic flux. Working: When the primary winding is connected to an ac supply mains, a current flows through it. Since, the winding links with an iron core, so current flowing through this winding produces as alternating flux in the core. This alternating flux links with the secondary winding. Due to Electromagnetic Induction, emf gets induced in the secondary winding. The induced emf in the secondary winding enables it to deliver current to an external load connected across it. Thus, energy is transferred from primary to secondary winding by means of Electomagnetic induction without any change in frequency.  

The transformer basically consists of two coils having mutual inductance and laminated steel core. The coils are insulated from each other and the steel core. Other necessary parts are: Some suitable container for assembled core and windings. a suitable medium for insulating the core and windings from the container. suitable bushings for insulating and bringing out the terminals of windings from the tank. In all types of transformers the core is constructed of steel sheet laminations assembled to provide a continuous magnetic path with a minimum of air gap included. The steel used is of high silicon content. The eddy current loss is minimized by laminating the core. The thickness of the laminations varies from 0.35mm for a frequency of 50 Hz to 0.5mm for a frequency of 25 Hz. The sheets are imbricated to avoid the narrow gaps through the cross section of the core. Types of Transformers On the basis of construction, transformers are of two types: 1. Core T

Insulation Coordination in Power System Under Electrical Transmission Insulation Coordination in Power System was introduced to arrange the electrical insulation levels of different components in the electrical power system including transmission network, in such a manner, that the failure of insulator, if occurs, confindes to the place where it would result in the least danmage of the system, easy to repair and replace, and results least disturbance to the power supply. When any over voltage appears in the electrical power system, then there may be a chance of failure of its insulation system. Probability of failure of insulation, is high at the weakest insulation point nearest to the source of over voltage. In power system and transmission networks, insulation is provided to the all equipment and components. Insulators in some points are easily replaceable and repairable compared to other. Insulation in some points are not so easily replaceable and repairable and the replacem

(Solve Any 3rd Degree Polynomial Equation) I'm putting this on the web because some students might find it interesting. It could easily be mentioned in many undergraduate math courses, though it doesn't seem to appear in most textbooks used for those courses. None of this material was discovered by me. -- ES You should know that the solution of ax2+bx+c=0 is There is an analogous formula for polynomials of degree three: The solution of ax3+bx2+cx+d=0 is (A formula like this was first published by Cardano in 1545.) Or, more briefly, x   =   {q + [q2 + (r-p2)3]1/2}1/3   +   {q - [q2 + (r-p2)3]1/2}1/3   +   p where p = -b/(3a),    q = p3 + (bc-3ad)/(6a2),    r = c/(3a) But I do not recommend that you memorize these formulas. Aside from the fact that it's too complicated, there are other reasons why we don't teach this formula to calculus students. One reason is that we're trying to avoid teaching them about complex numbers. Complex numbers (i.e., t

Learning Objectives 1. Working Principle of Transformer 2. Construction Details 3. EMF Equation of Transformer 4. Voltage Transformation Ratio 5. Losses in Transformer 6. No Load and on load operation 7. Testing of Transformation 8. Efficiency and Voltage Regulation 9. Kapp Regulation Diagram 10. Auto Transformer 11. Instrumental Transformer (C.T and P.T)