Electrical Question and Answers:

*What is different between grounding and earthings?

Grounding means connecting the neutral point of the load to the ground to carry the residual current in case of unbalanced conditions through the neutral to the ground whereas earthing is done in an electric equipment in order to protect he equipment in occurence of fault in the system. 

*How many types of colling system it transformers?

1. ONAN (oil natural,air natural)

2. ONAF (oil natural,air forced)

3. OFAF (oil forced,air forced)

4. ODWF (oil direct,water forced)

5. OFAN (oil forced,air forced). 

*Define IDMT relay?

It is an inverse definite minimum time relay.In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates.It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.

*what is the principle of motor?

Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.

*What is SF6 Circuit Breaker?

SF6 is Sulpher hexa Flouride gas.. If this gas is used as arc quenching medium in a Circuitbreaker means SF6 CB. 

*what is ACSR cable and where we use it?

ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution. 

*What will happen if DC supply is given on the primary of a transformer?
   Mainly transformer has high inductance and low resistance.In case of DC supply there is no inductance ,only resistance will act in the electrical circuit. So high  electrical current will flow through primary side of the transformer.So for this reason coil and insulation will burn out. 

Electrical Circuits:

A network, in the context of electronics, is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, every component in the network. There are a number of different techniques for achieving this. However, for the most part, they assume that the components of the network are all linear. The methods described in this article are only applicable to linear network analysis except where explicitly stated.

Definitions

Component	A device with two or more terminals into which, or out of which, charge may flow.
Node	A point at which terminals of more than two components are joined. A conductor with a substantially zero resistance is considered to be a node for the purpose of analysis.
Branch	The component(s) joining two nodes.
Mesh	A group of branches within a network joined so as to form a complete loop.
Port	Two terminals where the current into one is identical to the current out of the other.
Circuit	A current from one terminal of a generator, through load component(s) and back into the other terminal. A circuit is, in this sense, a one-port network and is a trivial case to analyze. If there is any connection to any other circuits then a non-trivial network has been formed and at least two ports must exist. Often, "circuit" and "network" are used interchangeably, but many analysts reserve "network" to mean an idealized model consisting of ideal components.
Transfer function	The relationship of the currents and/or voltages between two ports. Most often, an input port and an output port are discussed and the transfer function is described as gain or attenuation.
Component transfer function	For a two-terminal component (i.e. one-port component), the current and voltage are taken as the input and output and the transfer function will have units of impedance or admittance (it is usually a matter of arbitrary convenience whether voltage or current is considered the input). A three (or more) terminal component effectively has two (or more) ports and the transfer function cannot be expressed as a single impedance. The usual approach is to express the transfer function as a matrix of parameters. These parameters can be impedances, but there is a large number of other approaches, see two-port network.

Delta-wye transformation

A network of impedances with more than two terminals cannot be reduced to a single impedance equivalent circuit. An n-terminal network can, at best, be reduced to n impedances (at worst ⁿC₂). For a three terminal network, the three impedances can be expressed as a three node delta (Δ) network or a four node star (Y) network. These two networks are equivalent and the transformations between them are given below. A general network with an arbitrary number of nodes cannot be reduced to the minimum number of impedances using only series and parallel combinations. In general, Y-Δ and Δ-Y transformations must also be used. For some networks the extension of Y-Δ to star-polygon transformations may also be required.

Source transformation

A generator with an internal impedance (i.e. non-ideal generator) can be represented as either an ideal voltage generator or an ideal current generator plus the impedance.

·                     Norton's theorem states that any two-terminal network can be reduced to an ideal current generator and a parallel impedance.

·                     Thévenin's theorem states that any two-terminal network can be reduced to an ideal voltage generator plus a series impedance.

Nodal analysis

1. Label all nodes in the circuit. Arbitrarily select any node as reference.

2. Define a voltage variable from every remaining node to the reference. These voltage variables must be defined as voltage rises with respect to the reference node.

3. Write a KCL equation for every node except the reference.

4. Solve the resulting system of equations.

Mesh analysis

Mesh — a loop that does not contain an inner loop.

1. Count the number of “window panes” in the circuit. Assign a mesh current to each window pane.

2. Write a KVL equation for every mesh whose current is unknown.

3. Solve the resulting equations

Transfer function

A transfer function expresses the relationship between an input and an output of a network. For resistive networks, this will always be a simple real number or an expression which boils down to a real number. Resistive networks are represented by a system of simultaneous algebraic equations. However in the general case of linear networks, the network is represented by a system of simultaneous linear differential equations. 

In network analysis, rather than use the differential equations directly, it is usual practice to carry out a Laplace transform on them first and then express the result in terms of the Laplace parameter s, which in general is complex. This is described as working in the s-domain. Working with the equations directly would be described as working in the time (or t) domain because the results would be expressed as time varying quantities. The Laplace transform is the mathematical method of transforming between the s-domain and the t-domain.

This approach is standard in control theory and is useful for determining stability of a system, for instance, in an amplifier with feedback.

Electrical machines:

An Electrical machine is the generic name for a device that converts mechanical energy to electrical energy, converts electrical energy to mechanical energy, or changes alternating current from one voltage level to a different voltage level.

Electrical machines as employed in industry fall into three categories according to how they convert energy. Generators convert mechanical energy to electrical energy. Motors convert electrical energy to mechanical energy. Transformers change the voltage of alternating current.

Generator

An electric generator is a device that converts mechanical energy to electrical energy. A generator forces electrons to flow through an external electrical circuit. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. The source of mechanical energy, the prime mover, may be a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy.

There are two main parts of a generator which can be described in either mechanical or electrical terms. In mechanical terms the rotor is the rotating part of an electrical machine, and the stator is the stationary part of an electrical machine. In electrical terms the armature is the power-producing component of an electrical machine and the field is the magnetic field component of an electrical machine. The armature can be on either the rotor or the stator. The magnetic field can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator. Generators are classified into two types, AC generators and DC generators.

AC generator

An AC generator converts mechanical energy into alternating current electricity. Because power transferred into the field circuit is much less than power transferred into the armature circuit, AC generators nearly always have the field winding on the rotor and the armature winding on the stator.

AC generators are classified into several types. The first is asynchronous or induction generators, in which stator flux induces currents in the rotor. The prime mover then drives the rotor above the synchronous speed, causing the opposing rotor flux to cut the stator coils producing active current in the stator coils, thus sending power back to the electrical grid. The second type is synchronous generators or alternator, in which the current for the magnetic field is provided by a separate DC current source.

DC generator

A DC generator produces direct current electrical power from mechanical energy. A DC generator can operate at any speed within mechanical limits and always output a direct current waveform. Direct current generators known as dynamos work on exactly the same principles as alternators, but have a commutator on the rotating shaft which converts the alternating current produced by the armature to direct current.

Motor

An electric motor converts electrical energy into mechanical energy. The reverse process of electrical generators, most electric motors operate through interacting magnetic fields and current-carrying conductors to generate rotational force. Motors and generators have many similarities and many types of electric motors can be run as generators, and vice versa.

Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. They may be powered by direct current or by alternating current which leads to the two main classifications: AC motors and DC motors.

AC motor

An AC motor converts alternating current into mechanical energy. It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.

There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor, which only runs slightly slower or faster than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current. The second type is the synchronous motor, which does not rely on induction and as a result, can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet.

DC motor

The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary permanent magnets, and rotating electrical magnets. Brushes and springs carry the electric current from the commutator to the spinning wire windings of the rotor inside the motor. Brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical magnets on the motor housing. A motor controller converts DC to AC. This design is simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor.

An example of a brushless, synchronous DC motor is a stepper motor which can divide a full rotation into a large number of steps. The motor's position can be controlled precisely without any feedback mechanism as long as the motor is carefully sized to the application.

Transformer

A transformer is a static device that converts alternating current from one voltage level to another level (higher or lower), or to the same level, without changing the frequency. A transformer transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying electric current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.

Electrical Machines - Induction motor:

An induction motor or asynchronous motor is a type of alternating current motor where power is supplied to the rotor by means of electromagnetic induction.

An electric motor converts electrical power to mechanical power in its rotor (rotating part). There are several ways to supply power to the rotor. In a DC motor, this power is supplied to the armature directly from a DC source while, in an induction motor, this power is induced in the rotating device. An induction motor is sometimes called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Unlike the normal transformer which changes the current by using time varying flux, induction motors use rotating magnetic fields to transform the voltage. 

The current in the primary side creates an electromagnetic field which interacts with the electromagnetic field of the secondary side to produce a resultant torque, thereby transforming the electrical energy into mechanical energy. Induction motors are widely used, especially polyphase induction motors, which are frequently used in industrial drives.

What Is Variable Frequency Drive:

          A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives. Since the voltage is varied along with frequency, these are sometimes also called VVVF (variable voltage variable frequency) drives. 

          Variable-frequency drives are widely used. In ventilation systems for large buildings, variable-frequency motors on fans save energy by allowing the volume of air moved to match the system demand. They are also used on pumps, conveyor and machine tool drives.

Electrical Safety:-

There is a great deal of activity in the electrical industry concerning electrical safety. The focus is on the two greatest electrical hazards to workers: shock and arc-flash. In recent years significant knowledge has been gained through testing and analysis concerning arc-flash hazards and how to contend with this type of hazard. This hazard exists when a worker is working on or near exposed, energized electric conductors or circuit parts that have not been placed in an electrically safe work condition. If an arcing fault occurs, the tremendous energy released in a fraction of a second can result in serious injury or death. However, there is a great challenge in getting the message to the populace of the electrical industry so that safer system designs and safer work procedures and behaviors result. Workers continue to sustain life altering injuries or death.

            There are a multitude of things that can be implemented to increase electrical safety, from design aspects and upgrading systems, to training, implementing safe work practices and utilizing personal protective equipment. Not the entire rule for the industry and the law is ‘don’t work it hot’, Per OSHA. It says “Only Work on Equipment That Is in an Electrically Safe Work Condition”. The worker should follow appropriate work practices and wear appropriate personal protective equipment (PPE) for the specific hazard.

Collections: Notes On Electricity: Generation, Transmission & D...

Collections: Notes On Electricity: Generation, Transmission & D...: Electrical power system consist of 4 major categories: a. Generation System b. Transmission System c. Distribution System d. Utility Sys...

Centre Of Knowledge: How Does a Transformer Work?

Centre Of Knowledge: How Does a Transformer Work?: A transformer is an electrical device that takes electricity of one voltage and changes it into another voltage. You'll see transformers a...

"Electrical Basic Terms & Definitions"

• Alternating currents — The term alternating current refers to a current that reverses at regular recurring intervals of time and that has alternately positive and negative values.
• Alternating current (advantages) — As compared with DC, the advantage of AC is the reduced cost of transmission by use of high voltage transformers.
• Alternating currents (disadvantages) — As compared with DC, the disadvantages of AC are: The high voltage which renders it dangerous and requires more efficient insulation; alternating current cannot be used for such purposes as electroplating, charging storage batteries, etc.
• Alternating current (effects) — There are several effects of the AC to consider in determining the size of wires. Accordingly, allowance must be made for: Self induction, mutual induction, power factor, skin effect, eddy currents, frequency, resistance, electric hysteresis, etc..
• Ammeter — Measures the current flow in amperes in a circuit. An ammeter is
  connected in series in the circuit.
• Ampere — The practical unit of electric current flow. If a one ohm resistance is
  connected to a one volt source, one ampere will flow.
• Anode — The positive pole of a battery, or preferably the path by which the current passes out and enters the electrolyte on its way to the other pole;
  opposed to the cathode.
• Branch Circuit — The circuit conductors between the final over current device
  protecting the circuit and the outlet(s).
• Calorie — The French heat unit.
• Capacitance — Measure, in farads, or the opposition to voltage changes in an AC circuit, causing voltage to lag behind current; exhibited by condensers, two conductors separated by a nonconductor.
• Capacitive Reactance — The effect of capacitance in opposing the flow of alternating or pulsating current.
• Capacitor — A device used to boost the voltage to a motor. Running capacitors are used in starting winding to increase the running torque of the motor
  Starting capacitors are used in the starting winding to increase the starting torque of the motor. Two electrodes or sets of electrodes in the form of plates, separated from each other by an insulating material called the dielectric.
• Circuit — A complete path over which an electric current can flow.
• Circuit Breaker — A device designed to open and close a circuit by non automatic means and to open the circuit automatically on a predetermined over current without injury to itself when properly applied within its rating. Circuit breakers can be reset.
• Circuit (Series) — A circuit supplying energy to a number of devices connected in series. The same current passes through each device in completing its path to the source of supply.
• Close Circuit — A circuit permitting a continuous current.
• Coil — An assemblage of successive convolutions of a conductor. A unit of a winding consisting of one or more insulated conductors connected in series and
  surrounded by common insulation, and arranged to link or produce magnetic flux.
• Conductance — The measure of ease with which a substance conducts electricity, measured in ohms. It is the opposite of resistance and is expressed in mhos.
• Conductor — An electrical path which offers comparatively little resistance. A wire or combination of wires not insulated from one another, suitable for
  carrying a single electric current. Bus bars are also conductors. Conductors may be classed with respect to their conducting power as; (a) good; silver, copper, aluminum, zinc, brass, platinum, iron, nickel, tin, lead; (b) fair; charcoal and coke, carbon, plumb ago, acid solutions, sea water, saline solutions, metallic ores, living vegetable substances, moist earth; (c) partial; water, the body, flame, linen, cotton, mahogany, pine, rosewood, lignum vitae, teak, and marble.
• Coulomb — A unit of electrical charge; the quantity of electricity passing in one second through a circuit in which the rate of flow is one ampere.
• Cross — Any accidental contact between electric wires or conductors.
• Current — The movement of electrons through a conductor; measured in amperes, milliamperes, and microamperes.
• Cycle — A complete reversal of alternating current, passing through a complete set of changes or motions in opposite directions, from a rise to maximum, return to zero, rise to maximum in the other direction, and another return to zero. One
  complete positive and one complete negative alternation of current or voltage.
• Dead — Free from any electric connection to a source of potential difference and from electric charge. The term is used only with reference to current carrying parts that are sometimes alive.
• Deci — A Latin prefix often used with a physical unit to designate a quantity one-tenth of that unit.
• Decibel — Technically a measure of relative power levels. (b) A measure of the loudness of a bell, siren, horn, or other noise. (c) The strength of an audio signal.
• Deflection — The distance or angle by which one line departs from another.
• Diagram — A skeleton geometrical drawing, illustrating the principles of application of a mechanism.
• Diode — A two electrode electron tube containing an anode and a cathode. Diodes are used as rectifiers and detectors.
• Direct Current — A unidirectional current. It may be constant or periodically fluctuating, as rectified alternating current.
• Dissipation — Loss of electric energy as heat.
• Drop — The voltage drop developed across a resistor due to current flowing through it.
• E — Symbol for voltage.
• Earth — The ground considered as a medium for completing an electric circuit.
• Electrical Horsepower — 746 watts.
• Electrical Units — In the practical system, electrical units comprise the volt, the
  ampere, the ohm, the watt, the watt-hour, the coulomb, the henry, the mho, the joule, and the farad.
• Electric Circuit — The path (whether metallic or nonmetallic) of an electric current.
• Electrician — A person who is versed in the knowledge of electricity.
• Electricity — The name is given to an invisible agent known only by its effects and manifestations, as shown in electrical phenomena. Electricity, no matter how produced is believed to be one and the same thing.
• Electrocution — The destruction of life by means of electric current.
• Electromagnet — A magnet produced by passing an electric current through and insulated wire conductor coiled around a core of soft iron, as in the fields of a dynamo or motor.
• Electromotive Force (EMF) — An energy-charge relation that results in electric pressure (voltage), which produces or tends to produce charge flow.
• Electron — The smallest charge of negative electricity known.
• Energy Efficiency — The efficiency of an electric machine measured in watt hours or kilowatt hours; the watt hour efficiency.
• Farad — Practical unit of electrostatic capacity in the electromagnetic system. A
  condenser is said to have a capacity of one farad if it will absorb one coulomb ( that is, one ampere per second), of electricity when subjected to a pressure of one volt. The unit of capacitance.
• Faraday Effect — A discovery made by Faraday that a wave of light polarized in a certain plane can be turned about by the influence of a magnet so that the vibrations occur in a different plane.
• Fathom — A measure of length equal to six feet, used chiefly in taking soundings, measuring cordage, etc.
• Fiber Optics — Piping light is the science that deals with the transmission of light
  through extremely thin fibers of glass, plastic, or other transparent material.
• Fluorescence — That property by virtue of which certain solids and fluids become luminous under the influence of radiant energy.
• Force — An elementary physical cause capable of modifying the motion of a mass.
• Formula — A prescribed form, principle, or rule expressed in mathematical terms, chemical symbols, etc.
• Formulae — A rule or principle expressed in algebraic language.
• Frequency — The number of periods occurring in the unit of time periodic process, such as in the flow of electric charge. The number of complete cycles per second existing in any form of wave motion; such as the number of cycles per second of an alternating current.
• Fuse — A strip of wire or metal inserted in series with a circuit which, when it carries an excess of current over its rated capacity, will burn out. Also called a
  cutout.
• Galvanometer — A current indicator. It consists of a magnetic needle suspended within a coil of wire and free to swing over the face of a graduated dial. The movement of the needle shows the direction of the current and indicates whether it is a strong or weak one. There are numerous types of galvanometers such as; astatic, tangent, sine, differential, ballistic, and D’Arsonval.
• Generator — A general name given to a machine for transforming mechanical energy into electrical energy.
• Ground — A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth.
• Grounded — Connected to earth or to some conducting body that serves in place of the earth.
• Heat (electric) — The heat produced in a conductor by the passage of an electric current through it.
• Horsepower (hp) — Unit used to express rate of work, or power. One
  horsepower=746 watts. Work done at the rate of 33,000 foot pounds per
  minute or 550 foot pounds per second.
• I — Symbol for electric current.
• Impedance — The total opposition which a circuit offers the flow of alternating current at a given frequency; combination of resistance and reactance, measured
  in ohms.
• Induction — The process by which an electrical conductor becomes electrified when near a charged body and becomes magnetized.
• Input — The intake or energy absorbed by a machine during its operation, as
  distinguished from the output of useful energy delivered by it.
• Insulator — A device for fastening and supporting a conductor. Glass and porcelain are employed almost universally for supporting overhead wires.
• Ion — An electrically charged atom or radical.
• Jacobi’s Law — A law of electric motors which states that the maximum work of a motor is performed when its counter electromotive force is equal to one half the electromotive force expended on the motor.
• Joint — The tying together of two single wire conductors so that the union will be good, both mechanically and electrically.
• Joule’s Law — The law first stated by Joule, that the quantity of heat developed in a conductor by the passage of an electric current is proportional to the resistance of the conductor, to the square of the strength of the current, and to the duration of the flow.
• Kilovolt (kv) — A unit of pressure equal to one thousands volts.
• Kilowatt — A unit of electrical power, equal to one thousands watts. Electric power is usually expressed in kilowatts. As the watt is equal to 1/746
  horsepower, the kilowatt or 1,000 watts = 1.34 hp. Careful distinction should be made between kilowatts and kilovolt amperes.
• L — The symbol for inductance.
• Leakage — The escape of electric current through defects in insulation or other causes.
• Loss — Power expended without accomplishing useful work.
• Made Circuit — A closed or completed circuit.
• Mega-Volt — A unit of pressure equal to one million volts.
• Meter — An electric indicating instrument as a voltmeter, ammeter, etc.
• Negative — The opposite of positive. A potential less than that of another potential or of the earth. In electrical apparatus, the pole or direction toward
  which the current is suppose to flow.
• Network — An electric circuit in which the parts are connected in some special manner and cannot be classed as in series, in parallel, or in series-parallel.
• Neutron — A proton and an electron in very close union existing in the nucleus. A particle having the weight of a proton but carrying no electric charge. It is located in the nucleus of an atom.
• Ohm — The unit of electrical resistance. Resistance is one ohm when a DC voltage of one volt will send a current of one ampere through.
• Open Circuit — A circuit, the electrical continuity of which has been interrupted, as by opening a switch.
• Output — The current, voltage, power, or driving force delivered by a circuit or device.
• P — Abbreviation for power.
• Peak — The maximum instantaneous value of a varying voltage or current.
• Peak Current — The maximum value of an alternating current.
• Period — The time required for a complete cycle of alternating current or voltage; for 60 cycles per second, a period would be 1/60 second.
• Photoelectric — Descriptive of the effect which light has on electric circuits, through a device controlled by light.
• Positive — The term used to describe a terminal with fewer electrons than normal so that it attracts electrons. Electrons flow into the positive terminals of a voltage source.
• Power — The rate at which work is done; it is usually expressed as the number of foot pounds in one minute, that is, if you lift 33,000 foot pounds in one minute, you have done 1 horsepower of work.
• Proton — The smallest quantity of electricity which can exist in the free state. A positive charged particle in the nucleus of an atom.
• Quick-Break — A switch or circuit breaker that has a high contact opening speed.
• R — Symbol for resistance.
• Reactance — Opposition offered to the flow of AC by the inductance or capacity of a part; measured in ohms.
• Recovery Voltage — The voltage impressed upon the fuse after a circuit is cleared.
• Relay — An electromagnetic device which permits control of current in one circuit by a much smaller current in another circuit.
• Resistance — The opposition offered by a substance or body to the passage through it of an electric current which converts electric energy into heat.
  Resistance is the reciprocal of conductance.
• Resistance Drop — The voltage drop in place with the current.
• Resistor — An aggregation of one or more units possessing the property of electrical resistance. Resistors are used in electric circuits for the purpose of
  operation, protection, or control.
• Semiconductor — A name given to substances having only moderate power
  of transmitting electricity, and which may be said in that respect to, stand midway between conductors and insulators.
• Series Circuit — A circuit supplying energy to a number of loads connected in series, that is, the same current passes through each load in completing its
  path to the source of supply.
• Series Parallel Circuit — An electric current containing groups of parallel connected receptive devices, the groups being arranged in the circuit in series; a
  series multiple circuit.
• Short Circuit — A fault in an electric circuit or apparatus due usually to imperfect insulation, such that the current follows a by-path and inflicts damage or is wasted.
• Solenoid — A spiral of conducting wire, would cylindrically so that when an electric current passes through it, its turns are nearly equivalent to a succession of parallel circuits, and it acquires magnetic properties similar to those of a bar magnet.
• Spark — A discharge of electricity across a gap between two electrodes. The discharge is accompanied by heat and incandescence. Distinguish between spark and arc.
• Steady Current — An electric current of constant amperage.
• Switch — A device for making, breaking, or changing the connections in an electric current.
• Telsa Coil — A form of induction coil designed by Telsa for obtaining high voltages and frequencies; it consists of a primary of a few turns of coarse wire and a secondary of fine wire, both immersed in oil insulation; a Telsa transformer.
• Transformer — An apparatus used for changing the voltage and current of an
  alternating circuit. A transformer consists of primary winding, secondary winding, and an iron core. In principle, if a current is passed through a coil of wire encircling a bar of soft iron, the iron will become a magnet; when the current is is continued the bar loses its magnetization.
• Transistor — An active semiconductor device with three or more terminals. Transistors turn on instantly. They don’t require a warm-up time like a tube does.
  A transistor will last for years and very little voltage is needed.
• Unit of Current — The practical unit of current is the ampere, which is the current produced by a pressure of one volt in a circuit having a resistance of one ohm.
• Unit of Electric Work — The joule.
• Unit of Pressure — The volt, or pressure which will produce a current of one ampere against a resistance of one ohm.
• Unit of Resistance — The ohm, which is the resistance that permits a flow of one ampere when the impressed pressure is one volt.
• V — Symbol for volt.
• Volt — The practical unit of electric pressure. The pressure which will produce a current of one ampere against a resistance of one ohm.
• Voltage Drop — The drop of pressure in an electric circuit due to the resistance of the conductor.
• V-O-M meter — Volt-ohm-milliammeter, the troubleshooters” basic testing instrument.
• W — Symbol for wattage.
• Watt — The practical unit of power, being the amount of energy expended per second by an unvarying current of one ampere under the pressure of one volt.
• X — Symbol for reactance.
• Y connection — This method of transformer connection consists in connecting both the primaries and secondaries in star grouping.
• Z — Symbol for impedance.

Electricity:-

          Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire. In addition, electricity encompasses less familiar concepts such as the electromagnetic field and electromagnetic induction.

          In general usage, the word "electricity" adequately refers to a number of physical effects. In a scientific context, however, the term is vague, and these related, but distinct, concepts are better identified by more precise terms:

1. Electric charge: a property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.
2. Electric current: a movement or flow of electrically charged particles, typically measured in amperes.
3. Electric field: an influence produced by an electric charge on other charges in its vicinity.
4. Electric potential: the capacity of an electric field to do work on an electric charge, typically measured in volts.
5. Electromagnetism: a fundamental interaction between the magnetic field and the presence and motion of an electric charge.

          Electric power provided commercially by the electrical power industry. In a loose but common use of the term, "electricity" may be used to mean "wired for electricity" which means a working connection to an electric power station. Such a connection grants the user of "electricity" access to the electric field present in electrical wiring, and thus to electric power.

Electrical Engineering - Overview

           Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical power supply. It now covers a range of subtopics including power, electronics, control systems, signal processing and telecommunications.

           Electrical engineering may include electronic engineering. Where a distinction is made, usually outside of the United States, electrical engineering is considered to deal with the problems associated with large-scale electrical systems such as power transmission and motor control, whereas electronic engineering deals with the study of small-scale electronic systems including computers and integrated circuits.Alternatively, electrical engineers are usually concerned with using electricity to transmit energy, while electronic engineers are concerned with using electricity to process information. More recently, the distinction has become blurred by the growth of power electronics.

Sub-disciplines:

1. Power

2. Control

3. Electronics

4. Microelectronics

5. Signal processing

6. Telecommunications

7. Instrumentation

8. Computers