Wikipedia User:MohsinJahan

ELECTRICAL ENGINEERING Electrical power systems includes power generation, electrical power transmission & distribution, control & power system protection, electrical switchgear, power transformers, control & protection relays, transmission & distribution substations, and all switch yard equipment. All the very basic electrical engineering theories related to this field of technology are also included in this study site.This site is continually improving and in the near future we will add many other functionalities to this website to make it a complete solution for electrical technology. Please give your suggestions to help make the site better. This is a complete reference of electrical engineering and technology.

This site covers many important topics related to different parts of power system engineering, like, basic electrical, electrical power transformer, electrical switchgear, power system protection, electrical power transmission system etc. The site provides many video presentations for different electrical theories to make your electrical engineering study more easy and understandable. In few words, it can be said that this site covers almost all topics related to electrical power system engineering and technology. Electrical Engineering

electrical power system Electrical Power System The most familiar form of energy in our daily lives is electrical energy. The branch of engineering which deals with producing, managing and utilizing this energy, is referred as electrical engineering. This field of engineering was introduced in an organized manner in the mid of 19th century. Electrical technology is not as old as civil and mechanical technologies. Interest in this field of study grew after the invention of electricity. It was June 1752 when Benjamin Franklin first tried to catch electricity from clouds during a heavy storm with the help of a flying kite. This was the beginning and to date still we are trying to manage this energy. Managing electrical energy (producing, transmitting, distributing, utilizing) is nothing but electrical engineering. Commercially this became an occupation only after 1950. Electrical engineering is core engineering like civil and mechanical but it has a wide range of subfields. After modernization, many fields of engineering grew out of electrical such as electronics, computer, telecommunication engineering and many more. All the fields of study that directly or indirectly deal with electricity come under electrical engineering. In a power generation plant where electrical energy is produced, the application of this engineering is huge. All the mechanical and as well as electrical equipment involved in producing electrical energy, such as alternators, boilers, turbines etc. are controlled and protected by electrical signals. All the relays and switches involved in operation of the equipment are either electromechanical or static electronics devices. In the modern age, these devices are digitally controlled by computer software. So in addition to core electrical engineering, these electrical engineering subfields (electronic, computer, software engineering and IT) are also involved in power generation. When the voltage level of generated power is stepped up, electrical transformers are required. For proper control and protection of these transformers, a sophisticated switchgear system is required. Electrical switchgear includes all circuit breakers, electrical isolators, current transformers, potential transformers, control and protection relay system and many more. Modern electrical engineering deals with production, planning, operation, and maintenance of these systems. After stepping up the electrical power, it is transmitted to a load center. Huge electrical technology is involved in electrical power transmission systems and networks including large national grids. The problems associated with these systems are solved by electrical engineering including all engineering subfields. History of Electrical Engineering

Benjamin Franklin in 1752, was the first man who tried to utilize electricity from clouds by flying a kite during a stormy night. In 1780, Luigi Galvani was surprised when he saw that a dead frog’s leg twisted when it was touched by a silver and copper stick. He misunderstood the actual reason, thinking that the electricity came from the leg itself, and referred it as animal electricity. After development in 1800 by Alessandro Volta of the voltaic cell as a simple method of producing electricity from a chemical reaction, an actual revolution occurred in this field and the history of electrical engineering totally changed from this time. Benjamin Franklin Benjamin Franklin Luigi Galvani Luigi Galvani It is needless to say that most of the theories, on which this field of engineering is built, are related to electromagnetism. The law of electromagnetism was invented by Michael Faraday in the year 1831. This law is popularly known as Faraday’s law of electromagnetic induction. The relation between current and voltage in a conductor was already stated by Georg Ohm, in 1827. This is Ohm’s law. Based on these two theories development of electrical technology began. In his experiment with electromagnetic induction, Michael Faraday designed the most basic model of an electrical rotating machine. In 1873, James Clerk Maxwell, published his famous article on magnetism and electricity. Werner von Siemens the founder of the German multinational engineering and electronic company Siemens, made great contributions in the early days of the history of electrical engineering. He was a great inventor and developer. Another great contributor to the electrical engineering was Sir Thomas Edison. We all know him as inventor of electric light bulb in the year 1879. This invention was a revolution. He was also the builder of the first electrical supply network in the world. georg ohm Georg Ohm Alessandro Volta Alessandro Volta

Although there were so many developments and research works going on before 1882, the study of electricity was not recognized as a separate field of engineering. In that year electrical engineering was introduced as a separate branch of engineering by TU Darmstadt University Germany. This was the beginning of studying electrical engineering as a professional degree. In that very year Edison started the world’s first electric supply business at DC 110V. Initially, a total of 59 houses in Manhattan were connected to his network. Although, alternating current had already been developed in Europe in the year 1850 by Guillaume Duchenne, it was not yet commercially distributed. George Westinghouse, an American entrepreneur and engineer, finally came forward and financially supported the development of the AC power network. By the end of nineteenth century AC power transmission and distribution became popular and started dominating DC distribution systems. James Clerk Maxwell James Clerk Maxwell Michel Faraday Michel Faraday

After development of the distribution network, electricity reached consumers. After electricity reaches the consumer, it is utilized for operating different equipment run by electricity. Electrical engineering is also involved in developing such industrial and domestic equipment at the consumer end. Many scientists and engineers involved themselves in inventing and developing such equipment. A new window had been opened in history of electrical engineering. In 1895, Nikola Tesla transmitted radio frequency signal across a distance of eighty kilometers and developed radio transmitters. In 1897, the cathode ray tube was invented by Karl Ferdinand Braun and development of television technology began. In 1902, Willis Carrier developed air conditioning machines. Thomas Edison Thomas Edison Nikola Tesla Nikola Tesla In 1941, Konrad Zuse introduced the first form of programmable electromechanical computer. In 1943, Tommy Flowers produced first prototype of programmable digital computer. In 1946 Percy Spencer invented the microwave oven. Every day there are new inventions and developments in electrical engineering and technology. The discussion is far from over. Here, we tried to give an overview only. Modern Atomic Theory

As per modern atomic structure, the mass of an atom and its positive charge are concentrated in a tiny nucleus, while negatively charged electrons revolve around the nucleus in elliptical orbits. The central nucleus contains positively charged protons and neutral neutrons. Molecule is the smallest particle of a matter. A molecule consists of two or more same or different atoms. Atom is not the smallest physical particle in a matter. The smallest particle of an element does not remain in atomic form, it remains in molecular form. All kind of physical, chemical and electrical properties of molecule depend upon its atomic structure. Before, going to the actual matter, let's have a look at Dalton's Atomic Theory and then we will look into very basic concept of Modern Atomic Theory for understanding atomic structure more clearly. In the year 1808, a chemistry teacher John Dalton published his theory about atoms. At that time many unexplained chemical phenomenon got quickly unlocked by Dalton’s theory. Hence, the theory became a theoretical foundation in chemistry. The postulates of Dalton’s atomic theory were as follows. All matter is made up of small indivisible and indestructible particles called atoms. All atoms of the same element have identical properties, but differ from atoms of other elements. Atoms of different elements combine together to form a compound. A chemical reaction is nothing but rearrangement of these atoms. Atoms cannot be created or destroyed by any means. Dalton’s theory had certain drawbacks like; today we know that atoms can be destroyed. Also some atoms of the same elements vary in their mass(isotopes). The theory also fails to explain the existence of allotropes. Atomic Model

As per modern concept, atom mainly consists of electrons, protons and neutrons. The table below shows the mass and electric charge of electrons, protons and neutrons. electron proton mass From above table it is found that a proton is 1840 times heavier than an electron. The absolute value of electric charge of a proton and of an electron are same. So there must be same number of protons and electrons in an electrically neutral atom. The orbits along which the electrons revolve are also known as shells or energy levels. In atomic structure the successive shells are named as K, L, M, N, O, P, and Q as per increasing distance outwards from the nucleus. Each shell or energy level has maximum number of electrons for stability. This maximum number of electron in a shell can be given by the formula 2n2 where n is the shell number in sequential order outward from the nucleus. As per this formula, The maximum number of electron in first inner shell from nucleus is 2X12 = 2, The maximum number of electron in second inner shell from nucleus is 2X22 = 8, The maximum number of electron in third inner shell from nucleus is 2X32 = 18, and so on. These values are only applicable for inner shell or energy level of an atomic structure. For outer most shell of an atom the above rule is not applicable. After fulfilling the maximum numbers of electrons in different inner shells, the rest electrons would be in outer most shell of atom. Atomic Structure Atomic Structure

Let’s consider one copper atom, where number of electrons is 29. As per this rule the number of electrons in the first, second, third shells that is in K, L and M shell is 2, 8, and 18. The remaining 1 [29 − (2 + 8 + 18) = 1] electron will be in outer most shell i.e. fourth of N shell of the atom.

Every energy level or shell in atomic structure can further be sub-divided into different sub-shells or orbital. The number of sub shells or orbital in an energy level is equal to its denoting number. That means the energy level nearest to the nucleus will have one orbital or sub shell as that main shell is denoted as 1 (n = 1). The next nearer shell from nucleus will have two sub shells or orbitals as this is denoted as 2 (n = 2). Similarly third (n = 3) nearer shell from nucleus will have three orbital and so on. The orbital are denoted with s, p, d, f,.............. Among the orbital of one single shell the first orbital is denoted as s, second orbital is denoted as p, the third one is denoted as d and so on. So first shell will have one s orbital and is denoted as 1s. The second shell will have one s and one p orbital and they are denoted as 2s & 2p respectively The third shell will have one s, one p and one d orbital and they are denoted as 3s, 3p & 3d respectively and so on. Here we have another thing to remember that s orbital has one sub orbital and every sub orbital can contains maximum two electrons. The p orbital has 3 sub orbital and d orbital has 5 sub orbital. That means p orbital can contain maximum 6(3X2) electrons and d orbital can contain total 10 (5X2) electrons. The lower energy sub orbital are first filled up then next higher orbital is filled. There would not be any chance of filling up any higher orbital or sub orbital, before filling is completed in its lower orbital. If we go through the examples below it will be clear to us. Atomic Structure of Aluminum having 13 Electrons Atomic structure of aluminium Atomic structure of aluminium having 13 electrons Atomic Structure of Copper having 29 Electrons

Atomic structure of copper Atomic structure of copper having 29 electrons

Here it can be noticed that 3d orbital is in higher energy level than 4s Atomic Structure of Silver having 47 Electrons

Atomic structure of silver Atomic structure of silver having 47 electrons

Here it can be noticed that 3d orbital is in higher energy level than 4s similarly 4d orbital is in higher energy level than 5s similarly. Modern Atomic Theory

The modern atomic theory is just little more evolved than the Dalton’s Theory. Modern atomic theory is also called as quantum theory. The concept of wave particle duality comes into picture here. It says that the electrons which are considered to be particles can sometimes behave like waves. So an atom has a nucleus which is surrounded by probability clouds. These clouds are the most probably locations of electrons. The size and shape of these clouds can be calculated by using the equations of the waves. Nature of Electricity and Concept of Electricity

Electricity is the most common form of energy. Electricity is used for various applications; such as lighting, transportation, cooking, communication, production of various goods in factories and much more. None of us exactly know that what is electricity. The concept of electricity and theories behind it, can be developed by observing its different behaviors. For observing nature of electricity, it is necessary to study the structure of matters. Every substance in this universe is made up of extremely small particles known as molecules. The molecule is the smallest particle of a substance into which all the identities of that substance are present. The molecules are made up of further smaller particles known as atoms. An atom is the smallest particle of an element that can exist. There are two types of substances. The substance, that's molecules are made of similar atoms is known as an element. The matter whose molecules consisting dissimilar atoms, is called a compound. The concept of electricitycan be achieved from the atomic structures of substances. Structure of Atom

An atom consists of one central nucleus. The nucleus is made up of positive protons and charge less neutrons. This nucleus is surrounded by numbers of orbital electrons. Each electron has a negative charge of − 1.602 X 10 − 19 Coulomb and each proton in the nucleus has a positive charge of + 1.602 X 10 − 19 Coulomb. Because of the opposite charge there is some attraction force between the nucleus and orbiting electrons. Electrons have relatively negligible mass compared to the mass of the nucleus. The mass of each proton and neutrons is 1840 times the mass of an electron. As the modulus value of each electron and each proton are same, the number of electrons is equal to the number protons in an electrically neutral atom. An atom becomes positively charged ion when it loses electrons and similarly an atom becomes negative ion when it gains electrons. structure of atom Structure of Atom movement of free electronsAtoms may have loosely bonded electrons in their outermost orbits. These electrons require a very small amount of energy to detach themselves from their parent atoms. These electrons are referred as free electrons which move randomly inside the substance and transferred from one atom to another. Any piece of substances which as a whole contains an unequal number of electrons and protons is referred as electrically charged. When there is more number of electrons compared to its protons, the substance is said to be negatively charged and when there is more number of protons compared to electrons, the substance is said to be positively charged. The basic nature of electricity is, whenever a negatively charged body is connected to a positively charged body by means of a conductor, the excess electrons of negative body starts flowing towards the positive body to compensate the lack of electrons in that positive body.

Hope you got the very basic concept of electricity from the above explanation. There are some materials which have plenty of free electrons at normal room temperature. Very well known examples of this type of materials are, silver, copper, aluminium, zinc etc. The movement of these free electrons can easily be directed to a particular direction if the electrical potential difference is applied across the piece of these materials. Because of plenty of free electrons these materials have good electrical conductivity. These materials are referred as good conductor. The drift of electrons in a conductor in one direction is known as the current. Actually electrons flow from lower potential (-Ve) to higher potential (+Ve) but the general conventional direction of current has been considered as the highest potential point to lower potential point, so the conventional direction of current has been just opposite of the direction of flow of electrons. In non-metallic materials, such as glass, mica, slate, porcelain, the outermost orbit is completed and there is almost no chance of loosing electrons from its outermost shell. Hence there is hardly any free electron present in this type of material. Hence, these materials cannot conduct electricity in other words electrical conductivity of these materials is very poor. Such material are known as non - conductor or electrical insulator. The nature of electricity is to flow through a conductor while an electrical potential difference applied across it, but not to flow through insulator even high electrical potential difference applied across them. Definition of Drift Velocity

If a particle moves in a random manner in a space. That means it continually changes its directions and velocities in a random manner. The resultant of these random motions as a whole called drift velocity. The definition of drift velocity can be understood by imagining the random motion of free electrons in a conductor. The free electrons in a conductor moves with random velocities and in random directions. When an electric field is applied across the conductor the randomly moving electrons are subjected to electrical forces along the direction of the field. Due to this field, the electrons do not give up their randomness of motion, but they will be shifting towards higher potential. That means the electrons will drift towards higher potential along with their random motions. Thus, every electron will have a net velocity towards the higher potential end of the conductor and this net velocity is referred as the drift velocity of electrons. Hopping you understand the definition of drift velocity. The current due to this drift movement of electrons inside an electrically stressed conductor, is known as drift current. It is needless to say that every current that flows through a conductor is drift current. Drift Velocity and Mobility

There are always some free electrons inside any metal at room temperature. More scientifically, at any temperature above the absolute zero, there must be at least some free electrons if the substance is conductive in nature such as metal. These free electrons inside the conductor move randomly and frequently collide with heavier atoms and change their direction of motion every time. When a steady electric field is applied to the conductor, the electrons start moving towards the positive terminal of the applied electrical potential difference. But this movement of electrons does not happen straightway. During travelling towards the positive potential the electrons continuously collide with the atoms and bounced back in a random fashion. During the collision the electrons lose some of their kinetic energy and again due to the presence of electric field, they are re-accelerated towards the positive potential and regain their kinetic energy. Again, during further collision the electrons partly lose their kinetic energy in the same manner. Thus the applied electric field cannot stop the random motion of the electrons inside a conductor. Although in presence of applied electric field, the motion of the electrons is still random, but there will be over all resultant movement of electrons towards positive terminals. In other words, the applied electric field makes the electrons to drift towards positive terminal. That means the electrons get an average drift velocity. If electric field intensity is increased the electrons are accelerated more rapidly towards positive potential after each collision. Consequently the electrons gain more average drift velocity towards positive potential i.e. in the direction opposite to the applied electric field.

If ν is the drift velocity and E is the applied electric field.

Where μe is referred as electron mobility. Animation of Drift Velocity Drift Current and Electron Mobility

electron mobility Electron Mobility in Conductor The current caused by the steady flow of electrons due to drift velocity is called drift current. What is Electric Current?

Electric current is nothing but the rate of flow of electric charge through a conductor with respect to time. It is caused by drift of free electrons through a conductor to a particular direction. As we all know, the measuring unit of electric change is Coulomb and the unit of time is second, the measuring unit of current is Coulombs per second and this logical unit of current has a specific name Ampere after the famous French scientist André-Marie Ampere. If total Q Coulomb charge passes through a conductor by time t, then current I = Q / t coulomb par second or Ampere. For better understanding, let give an example, suppose total 100 coulombs of charge is transferred through a conductor in 50 seconds. What is the current? As the current is nothing but the rate at which charge is transferred per unit of time, it would be ratio of total charge transferred to the required time for that. Hence, here current I = 100 coulombs / 50 second = 2 Amperes. 'Ampere' is Sl unit of current. Definition of Electric Current

While a potential difference is applied across a conductor, electrical charge flows through it and electrical current is the measure of the quantity of the electrical charge flowing through the conductor per unit time. Theory of Electricity

There is an equal number of electrons and protons in an atom. Hence, atom is in general electrically neutral. As the protons in the central nucleus are positive in charge and electrons orbiting the nucleus, are negative in charge, there will be an attraction force acts between the electrons and protons. In an atom various electrons arrange themselves in different orbiting shells situated at different distances from the nucleus. bohr model of atomic structure Figure-1

The force is more active to the electrons nearer to the nucleus, than to the electrons situated at outer shell of the atom. One or more of these loosely bonded electrons may be detached from the atom. The atoms with lack of electrons are called ions. Due to lack of electrons, compared to number of protons, the said ion becomes positively charged. Hence, this ion is referred as positive ion and because of positive electrical charge; this ion can attract other electrons from outside. The electron, which was previously detached from any other atom, may occupy the outer most shell of this ion and hence this ion again becomes neutral atom. The electrons which move from atom to atom in random manner are called free elections. When a voltage is applied across a conductor, due to presence of electric field, the free electrons start drifting to a particular direction according the direction of voltage and electric field. This phenomenon causes current in the conductor. The movement of electrons, means movement of negative charge and rate of this charge transfer with respect to time is known as current. current The amount of negative electric charge in an electron is 1.602 X 10-19 Coulomb. Hence, one coulomb negative electric charge consists of 1/1.602 X 10 -19 = 6.24 X 10 18 number of electrons. Hence, during drift of electron to a particular direction, if 6.24 X 10 18 number of electrons cross a specific cross-section of the conductor, in one second, the current is said to be one ampere. Since, we have already seen the unit of current, ampere is coulomb/second. Measurement of Current

The most common method of measuring current is to connect an ammeter in series with the circuit that’s current to be measured. This is so because; the entire current flowing through the circuit must also flow through the ammeter also. The ideal internal resistance or impedance of an ammeter is zero. Hence, ideally there is no voltage drop across the ammeter connected in the circuit. A conventional analog ammeter consists of a current coil. Whenever current flows through this coil, it deflects from its position depending upon the amount of current flowing through it. A pointer is attached to the coil assembly; hence it points the current reading on the dial of the ammeter. For measuring alternating current, clip on meter or tong tester can also be used instead of conventional ammeter. In this ammeter a current transformer core is attached to the meter which can easily be clipped on the live current carrying conductor. Due to this arrangement, current in the circuit transforms to the secondary of the CT and this secondary current then measured on the dial of clip on meter without disturbing the continuity of the current unlike conventional ammeter. Conventional Flow of Current Vs Electrons Flow

conventional current flow In the early days, it was thought that the current is, flow of positive charge and hence currentalways comes out from the positive terminal of the battery, passing through the external circuit and enters in the negative terminal of the battery. This is called conventional flow of current. On the basis of this conception, all the theories of electricity, formulas, and symbols were developed. After the development of atomic nature of matter, we have come to know, that actual cause of current in a conductor is due to movement of free electrons and electrons have negative change. Due to negative charge, electrons move from the negative terminal to the positive terminal of the battery through the external circuit. So the conventional flow of current is always in the opposite direction of electrons flow. But it was impossible to change all the previously discovered subsequent rules, conventions, theories and formulas according to the direction of electrons flow in the conductor. Thus the concept of conventional current flow was adopted. The true electron flow is used only when it is necessary to explain certain effects (as in semiconductor devices such as diodes and transistors). Whenever we consider the basic electrical circuits and devices, we use conventional flow of current i.e. current flowing around the circuit from the positive terminal to the negative terminal. Types of Current

There are only two types of electrical current, direct current and alternating current. We abbreviate them as DC and AC respectively. Concept of DC was developed before AC. But AC becomes most popular means of generating, transmitting and distributing of electric power. The direction of the flow of direct current is unidirectional, means this current does not alter its direction during flowing. Most common examples of DC in our daily life, are the current that we get from all kinds of battery system. But most popular form of electrical current is alternatingcurrent or AC. AC does have some advantages over DC for generating, transmitting and distributing and that is why the current we get from our electric supply companies, is normally alternating current. Alternating Current

The current whose flow is not unidirectional moreover it alternates at a frequency, is calledalternating current. In other words, the direction of the current continuously changes from forward to backward and then backward to forward in the circuit. The number of times, this direction changes from forward to backward or from backward to forward per second, is referred as frequency of the current. The current produced in an alternator is always analternating current. The shape of the waveform of an alternating current is usually sinusoidal. But square, triangular and other types of waveform are also available for attending current. Conventional Direction of Alternating Current

As direct current, alternating current is denoted with arrow. An AC has both forward and backward direction of flow. The arrow head always indicates the forward direction of the current. In different point of view, when the current has a positive valve, the direction of currentis same as the reference arrow and when the current gets negative value; its direction is just opposite of the reference arrow. Effects of Electric Current

There are mainly two effects of current, such as heating effect and magnetic effect. Each and every utilization of electricity, we see in our daily life, is either due to heating effect or due tomagnetic effect of current. For examples, the light bulb glows in our house is due to heating effect of current and the fan rotates in our house is due to magnetic effect of current. There are thousands of other examples which can illustrate the effect of current, too. Heating Effect of Electric Current

Whenever current passes through a conductor there would be a generation of heat due to ohmic loss in the conductor. This is commonly known as heating effect of current. Since, we cannot use electric power directly, we need to convert it into another usable power, like heat, light, or mechanical power etc. When current flows through a conductor some loss occurs and this loss is almost inevitable, and more the resistance of the conductor, more the loss. This loss due to the electrical resistance of conductor is mainly responsible for the heating effect of current. As some electric power is converted into heat energy, this phenomenon can be described byJoule's law, which states that, H\; =\; i^2\cdot r\cdot t Where H is the generated heat in calories, i is the current that is flowing through the wire and it is measured in amperes, r is the resistance of the conductor in ohm(Ω) and t is the duration ofcurrent flowing in seconds. If we know the time of current flowing, the resistance of wire, and amount of current flow, we can easily find out the generated heat of the circuit. This heat can be utilized in various ways. We saw that the more the electrical resistance of the wire the more the generated heat in the circuit, but to know more accurately about the heating effect of current, we should know about it from the atomic level. As the flow of current is nothing but the flow of electrons there will always be resistance from the fixed atoms of the conductor. The fixed atoms of the wire resist the flow of electrons and as a result there are collisions and as the kinetic energy converts into heat energy we see that the wire is getting hot. Applications of Heating Effect of Electric Current

Now, the generated heat can be viewed from many points of angles. Sometimes, it is only seen as a loss and is trying to be minimized. Various steps are taken to minimize heat dissipation from the conductor. But we can see many positive applications of heating effect of current in our daily life. Electric iron, the whole idea or working principle depends upon the heating effect of current. High resistant wire is used as the main coil in the electric iron when current flows through the coil, the coil gets heated and the iron works. But what about over heating of electric iron? This problem can be solved by using bimetallic conductors. Bimetallic plates made of two different metals are used in the circuit. As expansion co-efficient of heat is different for two metals, so due to heating effect one metal's expansion is different from the other metal; as a result the plate is bent and after reaching at a certain temperature the contact of the circuit is broken and current flowing through the coil is stopped and the electric iron too is not heated any more. The same mechanism is used in electric heater, the only difference is that there is no bimetallic plate or circuit breaker involved. Another application of heating effect of current is seen in electric bulbs. The wire which is used inside the bulb gets illuminated and emits light after reaching certain temperature. The metal used in the bulb is mainly made of tungsten. Finally and perhaps the most important application of the heating effect of current is inelectrical fuses, that are used in almost everywhere. From huge industries to domestic level, everywhere electrical fuse is a must. The fuse is made of such metals which has a certain melting point. They are okay for normal current but when over current flows through the circuit; the generated heat in the fuse wire is enough to melt the metal portion of the fuse wire and break the circuit. In this way the costly equipment is protected as huge current flow, can damage the equipment permanently. Magnetic Effects of Electric Current

Magnetic Field due to Current Carrying Conductor

In 1819, it was discovered by a Danish Physicist, Hans Christian Oersted that an current is always accomplished by certain magnetic effect. He observed a current carrying conductor when placed near a magnetic needle; the needle deflects to a certain direction. He also observed that when the direction of current in the conductor is reversed, the needle deflects in opposite direction. That means there is a magnetic field due to current carrying conductor. Further investigation shows that, the magnetic field around the conductor consists of a number of concentric closed lines of force. If we pass an current through a conductor through a card board as shown in the figure and try to plot the field with the help of a magnetic needle on that card board, we shall get the magnetic lines as shown in figure. These are all closed circles and concentric with the conductor. Now if we reverse the current in the conductor and repeat the same experiment as shown in the figure, we shall get the oppositely directed closed circular magnetic lines, concentric with the conductor as shown. Magnetic field due to a current  carrying conductor From the above experiment it is also found that when current flows through the conductor in upward direction, the direction of circular magnetic lines are anti clockwise if we observe from the top. On the other hand; if the current flows through the conductor in downward direction, the circular magnetic lines are clockwise if we observe from the top. Properties of magnetic field due to a current carrying conductor can be summarized as below, All lines of magnetic field are circular in shape, symmetrical to each other and concentric with the axis of current carrying conductor. The radius of the lines of force increases as we go away from the axis of the conductor. The direction of magnetic circular line depends upon the direction of flow of currentthrough the conductor. The magnetic flux density of the induced magnetic field around the conductor increases if the current flowing through the conductor is increased and it decreases if the current is decreased. Determination of Direction of magnetic field around a Current Carrying Conductor. There are mainly two popular rules for determining the direction of magnetic field due to acurrent carrying conductor and these are Cork screw rule and Right hand rule. Cork Screw Rule

Cork Screw Rule Cork Screw Rule

If the right handed cork screw is held with its axis parallel to the conductor pointing the direction of flow of current and the head of the screw is rotated in such a direction that the screw moves in the direction of flow of current, then the direction in which the head of screw is rotated, will be the direction of magnetic lines of force. Right Hand Rule

Right Hand Rule Right Hand Rule

If the current carrying conductor is held in right hand by the observer so that it is encircled by fingers stretching the thumb at right to the fingers in the direction of flow of current then finger tips will point the direction of magnetic lines of force. --MohsinJahan (talk) 11:07, 12 November 2014 (UTC)www.MohsinJahan.Weebly.comCLICK HERE FOR MORE TECHNICAL THINGS