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From its beginnings in the late nineteenth century, electrical engineering has blossomed from focusing on
electrical circuits for power, telegraphy and telephony to focusing on a much broader range of disciplines.
However, the underlying themes are relevant today: Power creation and transmission and information
have been the underlying themes of electrical engineering for a century and a half. The fundamental laws governing Electrical Engineering are as follows:-
Ampere's Circuital Law
Lorentz's Force Law
Fleming's Right hand and Left hand Rule
According to this law, if there is no change in the physical state of a conductor then the ratio of the potential difference applied at its ends and the current flowing through it is constant. Thus if the potential difference at the ends of the conductor be V and the current flowing through it be i, then according to Ohm's law we have
R = V/i
A graph drawn between the applied potential difference which V and the current i flown through the conductor is straight line. Ohm's law is true for metallic conductors only.
Ohm's law is not sufficient to give current in complicated circuits.There are two laws given by Kirchhoff in 1842 namely Kirchhoff's Current Law or KCL and Kirchhoff's Voltage Law or KVL
Kirchhoff's Current Law(KCL)
It is also called as junction law. In an open circuit the algebraic sum of currents meeting at a point is zero. This is also called as point rule.
Let I1 and I2 are meeting at O in AO and BO direction and I3, I4 and I5 currents are leaving the point O in OC, OD and OE directions. Assuming that current reaching at junction O are positive and current leaving junction O are negative then,
I1 + I2 + [-I3] + [-I4] + [-I5] = 0
i.e., I1 + I2= I3 + I4 + I5
Kirchhoff's Voltage Law(KVL)
In a closed circuit the algebraic sum of the product of currents and resistances of different parts of loop is equal to the algebraic sum of the e.m.f. in the loop.
I1R1 + I2R2 - I3R3 = E
The direction of emf induced in a conductor or coil is governed by Lenz's Law which states that the direction of induced emf would be in such a direction that it would try to oppose the very cause for which it is due.
Induced emf, e = - NdΦ/dt
Faraday's Laws of Electromagnetic Induction
Faraday's First Law:-
This law states that, "when the flux linking with the coil or circuit changes an emf is induced in it or whenever the magnetic flux is cut by the conductor an emf is induced in the conductor."
Faraday's Second Law:-
This law states that magnitude of emf induced is directly proportional to the rate of change of flux linking the coil.
i.e., induced emf, e ∝NdΦ/dt
where NdΦ/dt is product of number of turns and rate of change of linking flux and is called rate of change of flux linkage.
The force of attraction between the two charges Q1 and Q2 is directly proportional to the product of the two charges and inversely proportional to the square of the distance between the two charges.
F = k Q1Q2/R2
where k is proportionality constant.
On April 21, 1820 Danish Physicist Hans Christian Oersted discovered the magnetic field produced by an electric field.
Ampere's Circuital Law
The line integral of vector H over the whole contour depends only on the algebraic sum of the currents intersecting the surfaces, and is equal to that sum i.e.,
∮H.dl = ∑ I
The above equation is known as Ampere's circuital law or sometimes referred to as Ampere's work law.
Biot - Savart's Law
It states that the magnetic flux density dB is directly proportional to the length of the element dl, the current I and the sine of angle Θ between the direction f the current and vector joining a given point of the field and the current element, and is inversely proportional to the square of the distance of the given point from the current element r,
where K is proportionality constant and is dependent upon the magnetic properties of the medium and the system of units employed.
Lorentz's Force Law
Lorentz's Force, the force exerted on charged particle q moving with velocity v in an Electric field E and Magnetic field B. The entire force on the charged particle is called the Lorentz force and is given by
F = qE + qv × B.
According to this theorem, the total electric Ψ flux emanating from a closed surface is equal to the total charge enclosed by the surface.
Ψ = ∫∫ D. ds
Fleming's Right Hand Rule
According to Fleming's right hand rule if the thumb, fore-finger and middle finger of the right hand are held mutually perpendicular to each other, fore-finger pointing in the direction of the field and thumb in the direction of motion of conductor then middle finger will point in the direction of induced emf.
Fleming's Left Hand Rule
When a wire carrying electric current is moved in a magnetic field of a magnet, the magnetic field induced by the wire reacts with the magnetic field of the magnet causing the wire to move outwards. Fleming's left hand rule helps to predict the movement. According to Fleming's right hand rule if the thumb, fore-finger and middle finger of the left hand are held mutually perpendicular to each other, the fore-finger points in the direction of magnetic field, thumb in the direction of movement of wire then the middle finger will point in the direction of current.
Note:- This above explanation of various fundamental laws of electrical engineering are just an introduction to them and they are briefly described in various in our website.
A transmission line has four constants R, L, C and shunt conductance. But generally, three constants R, L and C are considered and they are uniform along the whole length of line. The fourth constant shunt conductance between conductors or between conductor and ground and accounts for the leakage current at the insulators. It is very small in case of overhead lines and may be assumed zero. The capacitance existing between conductors for 1φ line or 3φ line forms a shunt path throughout the length of line. Therefore capacitance effects introduce complication in transmission line calculation. Depending upon the manner in which capacitance is taken into account, the overhead transmission line are classified as, Short transmission linesMedium transmission linesLong transmission lines
Short transmission linesA short transmission line is one in which the line voltage is comparatively low (< 20kV) and the length of an overhead transmission line is upto about 50km. Due to smaller length and …
Group DrivesIt consists of single machine which actuates several machines or mechanism by means of one or more line shaft. Hence this is also called "line shaft drive". This line shafts are connected to multi stepped pulleys and belts that connect this pulley and shaft of the driven machine, serves to vary their speed.
Group drive is economical in consideration for the cost of motor and control gear. A single motor of large capacity costs less than that of the total cost of number of small motors for same total capacity namely, a single motor of 100KW costs less than that of ten motors of 10KW each. Since all the motors may not operate on full load at the same time, the KW rating of motor of group drive is often less than the aggregate KW output rating of the individual motor and further cause reduction in cost. Individual DriveIn individual drive an electric motor used for transmitting motion to various parts or mechanism belonging to single equipment. For example, such drive…
An induction motor with two cage rotor is used for high starting torque. The slotting arrangement for double cage induction motor is as shown in above figure. As the name indicate the double cage induction motor has two winding in rotor. The outer bars consists of rotor bars having low reactance and high resistance. On the other hand, the inner cage consists of rotor bars having high reactance and low resistance.
At start the rotor frequency is high, the outer cage carries most of the current despite its high resistance. The inner cage has low reactance and is mostly ineffective. This gives high starting torque and low starting current. As the motor picks up the speed, the rotor frequency reduces and the inner cage carries most of the current. Under normal running condition, the outer cage and inner cage are in parallel giving low combined resistance and both the cages are active.
When the speed is normal frequency reduces and it is so small that the reactance of…
An induction motor consists of two main parts StatorRotor
The stationary frame is called stator and the rotating armature is called rotor. The stator of induction motor is similar to that of the synchronous motor or generator. It is made of large number of stampings. These stampings are slotted in order to receive the stator windings. Figure below shows the construction of Induction motor.
The functions of various parts is as follows:-Frame:- Its function is to provide mechanical support to the entire construction. The frame also contains the stator winding of Induction motor.Air gap:- Air gap provides the space for the rotating magnetic field between the stator and rotor.Fan:- The fan rotates with the rotor. Its function is to cool down the motor.Slip rings:- The rotor winding terminals are permanently connected to the slip rings(in slip ring type induction motor). The slip rings are continuously in contact with the brushes which are pressed against slip rings. Externa…
When the anode voltage voltage is made positive with respect to the cathode, the junctions J1 and J3 are forward biased but the middle junction J2 is reverse biased and only a small leakage current flows from anode to cathode due to the mobile charges. The junction J2, because of the presence of depletion layer does not allow any current to flow through the device. The leakage current is insufficient to make the device conduct. The depletion layer mostly of immovable charges does not constitute any flow of current. The SCR is then said to be in the forward blocking or OFF sate condition and the leakage current is known as OFF state current ID. When the cathode voltage is positive with respect to the anode, the middle junction J2 becomes forward biased but the two outer junctions J1 and J3 becomes reverse biased. This is like two series connected diodes with reverse voltage across them. The junction J1 and J3 do not allow any current to flow through the device. Only a very small leakage…
Crawling It has been found that induction motor practically this squirrel cage type ,sometimes exhibit,a tendency to run stable at speeds as low as 1/7th of their synchronous speed .This is known as crawling of induction motor. This action is due to ,the fact that the AC winding of the stator produces a flux wave which is not pure sine wave .It is a complex wave consisting of a fundamental wave which revolves synchronously and odd harmonics like 3rd,5th,7th etc. which rotate either in the forward or backward direction at Ns/3, Ns/5, Ns/7 speed respectively. As a result in addition to the fundamental torque ,harmonics torques also developed whose synchronous speed for fundamental torque. For Example Ns/n, where N is the order of harmonics torque. Since the 3rd harmonics current are absent in a balanced three phase system ,they produce no torque .Hence total motor torque has there components. The fundamental torque rotating with synchronous speed Fifth harmonics torque rotating at Ns/5…