Electrical World

When charges are separated, a space is created where forces are exerted on the charges. An electric field is such a space. Depending upon the polarity of the charges, the force is either attractive or repulsive. Therefore, we can say that static charges generate an electric field. An electric field influences the space surrounding it. Electric field strength is determined in terms of the force exerted on charges. A capacitor is a reservoir of charge. The two parallel plates of a capacitor, when connected to a voltage source, establishes an electric field between the plates. The positive terminal, or pole of the voltage source will draw electrons from plate 1 whereas the negative pole will push extra electrons on to plate 2. Voltage across the capacitor will rise. The capacitor gets charged equal to the voltage of the source. The capacitance of a capacitor is a measure of its ability to store charge. The capacitance of a capacitor is increased by the presence of a dielec

Several theories have been developed to explain the nature of electricity. The modern electron theory of matter, propounded by scientists Sir Earnest Rutherford and Niel Bohr considers every matter as electrical in nature. According to this atomic theory, every element is made up of atoms which are neutral in nature. The atom contains particles of electricity called electrons and protons. The number of electrons in an atom is equal to the number of protons. The nucleus of an atom contains protons and neutrons. The neutrons carry no charge. The protons carry positive charge. The electrons revolve round the nucleus in elliptical orbits like the planets around the sun. The electrons carry negative charge. Since there are equal number of protons and electrons in an atom, an atom is basically neutral in nature. If from a body consisting of neutral atoms, some electrons are removed, there will be a deficit of electrons in the body, and the body will attain positive charge

If a fault occurs in the underground cable, it is essential that the type of the fault and location of the fault should be determined as quickly and accurately as possible. Accuracy is important in order to avoid excessive trenching work. The type of fault which is most likely to occur is single conductor to ground fault. In multi-core cables, the fault current will likely give rise to excessive heating at the fault causing further damage to the insulation and extending the fault to remaining conductors. Open circuit faults may occur occasionally which be usually at cable joints.  Cable fault type identification:  Prior to the location of the fault on the power system it is important to determine the type of fault so as to make a better choice of the method to be used for fault location Isolate the faulty cable and test each core of the cable for earth fault. One terminal of the insulation tester is earthed and each conductor of the cable is in turn touched with

Silicon Carbide Arresters (SIC): The Non linear lightning arrester basically consists of set of spark gaps in series with the silicon carbide non linear resistor elements. Lightning arresters are connected between the phase conductors and ground. During normal system operating voltage conditions, the spark gaps are non conducting and isolate the high tension (HT) conductors from the ground. However whenever an overvoltge of magnitude dangerous to the insulation of the apparatus protected occurs ( these over voltages or over surges may be caused due to lightning strikes on the conductors or due to Extra High Voltage (EHV) switching) the spark gap breaks down and allows the high voltage surge current to flow through the ground. Working Principle of Silicon Carbide (SIC) Lightning Arresters: The volt-ampere characteristics of the non linear resistor in the lignting arrester can be approximately described by expression V = KI β . Where K and β are dependent on the co

Why star delta starter is preferred with induction motor? Star delta starter is preferred with induction motor due to following reasons: • Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. • Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused. • In addition, starting torque is increased and it prevents the damage of motor winding. State the difference between generator and alternator Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor

we are providing the list of the top electrical mini projects ideas in this page. As many engineering students are searching for the best electrical projects from the 2nd year and 3rd year, we are providing this list of projects. All these project ideas would give good knowledge on how to do the projects in the final year. So, we hope this list of electrical mini projects ideas are more helpful for many engineering students. You may write your comments and new projects ideas also by visiting our contact us page. Top Electrical Mini Projects List:   Auto Night Lamp Using LED : Auto Night Lamp Using High Power LEDs is a circuit which turns ON the LED lights interfaced to it at night time and it turns OFF the lights automatically when it is day.   Anti Bag Snatching Alarm : This is a simple alarm circuit to thwart snatching of your valuables while travelling. The circuit kept in your bag or suitcase sounds a loud alarm, simulating a police horn, if someone attem

Let us consider the following two cases: Equal voltage ratios. Unequal voltage ratios. 1.39.1 Equal Voltage Ratios Assume no-load voltages E A and E B are identical and in phase. Under these conditions if the primary and secondary are connected in parallel, there will be no circulating current between them on no load. Figure 1.48 Equal Voltage Ratios Figure 1.48 shows two impedances in parallel. Let R A , X A and Z A be the total equivalent resistance, reactance and impedance of transformer A and R B , X B and Z B be the total equivalent resistance, reactance and impedance of transformer B . From Figure 1.48, we have E A = V 2 + I A Z A      (1.71) and           E B = V 2 + I B Z B      (1.72) ∴       I A Z A = I B Z B ∴     Equation (1.73) suggests that if two transformers with different kVA ratings are connected in parallel, the total load will be divided in proportion to their kVA ratings if their equivalent impedances are inversely proport

Q1: Where do we require single-phase induction motors? Ans: Single-phase induction motors are required where (i) 3 phase supply is not available  (ii) efficiency is of lesser importance (iii) Rating is less than one H.P.  (iv) Equipment is portable Q2: Why is the power factor of a single-phase induction motor low? Ans: It is due to the large magnetizing current which ranges from 60% to 70% of full-load current. As a result, even at no-load, these motors reach temperatures close to the full-load temperature. Q3: What is the function of centrifugal starting switch in a single-phase induction motor? Ans: The centrifugal switch is connected in series with the starting winding. The primary function of the centrifugal switch is to produce rotating flux in conjunction with main winding at the time of starting. When the motor has started and reaches nearly 75% of synchronous speed, it produces its own rotating field from the cross field effect. The starting winding n

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At room temperature of 300°K, it requires an energy of E G = 1.12 eV to break covalent bonds in Silicon material and E G = 0.7 eV to break the covalent bonds in Germanium material and to produce some ‘electron–Hole pairs’. Even at room temperature, a few of the covalent bonds will be broken, leading to equal number of electrons and Holes in Conduction Band and Valence Band, respectively. Electrons in the Conduction Band and Holes in the Valence Band, in an intrinsic semiconductor, are shown in Fig. 2.12. Small dashes represent free or conduction electrons. Holes are represented by circles in valence band. Fig. 2.12 Energy-band diagram for an intrinsic semiconductor

The value of conductivity of a material gives us an estimate of the extent to which a material supports the flow of current through it. Electrical conductivity depends upon the number of electrons available in the conduction process. The concept of conductivity is useful in many engineering applications including medical electronics. J = nqμE Equation (2.17) derived in the previous section can also be written as is called as conductivity of the material. Thus, electrical conductivity of a material is defined as the ratio of current density J and electric field intensity E . Conductivity of semiconductor materials increases with temperature, as an increase in temperature causes increase in conduction current. This is due to increase in broken covalent bonds that result in more charge carriers for current flow. So more electrons from Valence Band jump to Conduction Band with increase in temperature. The conductivity of semiconductors varies comp

Currents in metals are due to the movement of charge carriers ‘electrons’. where I is the current in Amperes and A is the cross-sectional area of conducting medium in metre 2 . Describing current density J as current per unit area has the advantage, since the dimensions of the conducting medium are not directly involved. Relation between current density and charge density ρ is described in the following: Current density: Current I (Amperes) through a conductor by definition is Charge (in Coulombs)/ Time (in seconds). Current is due to the movement of charges through a conducting medium in a given time. If, 1 C of charge moves through a conducting medium in 1 s, the resulting current is 1 A. electrons carry 1 Coulomb of charge. So the movement of 6.25 × 10 18 electrons for 1 s contributes to 1 A of current in a conductor. where q is the charge of an electron and N is the number of electrons in a given volume. If the charge passes through a distan

Conduction in conductors and semiconductors Mobility μ : In good conductors like metals, free electrons exist in abundance. They are supposed to be accelerated under the influence of electric or magnetic field as per ballistic (dynamics) laws. But in practice it is found that the electrons move with a constant velocity proportional to the field. The reason for this is the random nature of the electron movement involved in repeated collisions. The loss of energy during collisions is supplemented due to acceleration caused by the applied field E . Thus it is observed that the random motion of electrons when resolved in the direction of the field, the electrons acquire a constant speed called the drift speed v that is proportional to the field E (V /m) and velocity v is in metres/second. where μ is the constant of proportionality. μ is called as mobility. It is measured as m 2 /V-s. Mobility of electrons and Holes due to the influence of electric field is give

Purest semiconductor is known as intrinsic semiconductor . At 0°K, semiconductor behaves like an insulator, because energies of the order of E G cannot be acquired from an electric field. At room temperature, covalent bonds in the semiconductor may be broken into a few Hole–electron pairs, contributing to current flow through the material allowing the conductivity to increase. With respect to energy, if an electron is given additional energy, it breaks away from its covalent bond. When the free electron enters a Hole in a Valence Band, this excess energy is released as a quantum of heat or light. In turn this quantum of energy may be reabsorbed by another electron to break its covalent bond and create a new Hole–electron pair. Thus Holes and electrons appear to move. The moving charge carries form current. Ohm's law governs the conduction phenomena in conductors and resistors. Conduction by Holes is less when compared to that of electrons because of differences i

When voltages are applied, materials offer different values of electrical resistances to the passage of currents through them. On the basis of electrical resistances, materials are classified as conductors, semiconductors and insulators . In solids, available energy states for the electrons form ‘bands of energy levels’ instead of discrete energy levels in atoms. Conductors: Materials with adjacent or over-lapped conduction and Valence Bands with zero forbidden band-gap energy ( E G = 0) are known as conductors . EBD for a conductor material is shown in Fig. 2.7. Fig. 2.7 Energy-band diagrams for conductors Initially, the energy levels in the Conduction Band are empty. But, electrons enter the Conduction Band due to increase in temperature or energy acquired from an applied electric field. Then the electrons move freely inside the Conduction Band as charge carriers with each electron carrying an electron charge q n = 1.6 × 10 –19 C. So in a conductor, elec

Energy-band Concepts of Materials The electron energy levels for a single free atom in a gaseous medium are discrete, since the atoms are sufficiently far apart. So the energy levels of individual atoms are not perturbed. The proximity of neighbouring atoms in solid media such as crystals does not appreciably affect the energy levels of inner shell electrons. But, groups of energy levels of outer shell electrons are changed due to the influence of electrons in the neighbouring atoms. They allow sharing of electrons among them to form covalent bonds between neighbouring atoms in the process of getting on to stable ‘8-electron configuration’ in Silicon and Germanium semiconductors. Sharing of outer shell electrons to form covalent bonds is shown in Fig. 2.5. Valence band The coupling between the outer shell electrons of the atoms results in a group or a band of closely spaced energy levels or states instead of the widely spaced energy levels of the isolated atoms.

Fig. 2.3 Electron configuration of germanium atom Germanium semiconductor atom has ‘atomic number’ Z = 32. It has 32 positive charges in the nucleus and 32 electrons in various shells containing 2, 8, 18 and 4 electrons. Germanium atom is electrically neutral. Germanium semiconductor as a whole is electrically neutral. First, second and third orbits are completely filled. Fourth orbit (shell) is partially filled. Energy levels from fifth orbit onwards are empty energy levels. Germanium atom representation is shown in Fig. 2.4. It is a basis to know the formation of covalent bonds and so on. Germanium is also considered as a ‘tetravalent’ material, as it has 4 valence electrons in its outer incomplete shell. Thus, Silicon and Germanium materials are referred as tetravalent materials with similar electrical and chemical properties. Fig. 2.4 Representation of germanium atom with four valence electrons