Self Study World

Carey Foster Bridge Howdy Friends, this post gives data about the Carey Foster bridge. We will likewise figure out how this bridge can be utilized to decide the opposition in detail by inferring an articulation for deciding obstruction. Carey-Foster bridge Experiment We have just observed some essential strategies for estimating medium protections. Carey foster bridge is the strategy utilized for the estimation of medium opposition. Carey foster bridge is exceptionally utilized for the correlation of two equivalent protections. The circuit for Carey-Foster Bridge appears in the figure beneath. A slide wire having length L is incorporated among R and S. opposition P and Q are balanced with the goal that the proportion P/Q is around equivalent to R/S. this can be accomplished by sliding contact on slide wire. Carey Foster Bridge Working Principle The working guideline of the Carey Foster bridge is like the Wheatstone bridge. The potential fall is specifically relative to the length of th

Streamer Theory of Breakdown in Gases According to the Townsend theory firstly, current growth occurs as a result of the ionization process only. But in practice, breakdown voltages were found to depend on the gas pressure and the geometry of the gap. Second chances time lags of the order of 10-5 s, but practically it was observed to occur at a very short time of 10-8 s. Also, the Townsend mechanism predicts a very diffused form of discharge, that actually discharges were found to be filamentary and irregular. Townsend's mechanism failed to explain all these observed phenomena and as a result, The Streamer theory was proposed. The theory predicts the development of a spark discharge directly from a single avalanche in which the space charge developed by the avalanche itself is said to transform the avalanche into a plasma steamer. In Fig 1.7, a single electron starting at the cathode by ionization builds up an avalanche that crosses the gap. The electrons in the a

Encoder and Decoder Like a decoder, the encoder also provides the conversion of binary information from one form to another What is Encoder The encoder performs the opposite function of a decoder.  I t gives information in a more compact form.  The encoder has more input lines than output lines or says the output lines are less than the input lines. It has m input lines and n output lines. From m input lines, only one is activated at a time and gives an equivalent code on n output lines.  The block diagram of the encoder is shown in fig.1.The encoder is a digital or combinational circuit that converts an active signal into a coded output signal. Encoder circuit Encoder circuit[/caption] Encoder applications Encoders are used to reduce the number of bits needed to represent the given information. The practical use of encoders is for transmitting information in a digital system. Encoding is also useful if the information is to be stored for later use because fewer bits are required to b

Asynchronous And Synchronous Counter COUNTERS The counter is a sequential circuit that is used to count the number of clock pulses of the circuit. It is basically a digital system that counts a prescribed sequence of states upon application of input pulses.  The input pulses (also known as count pulses) can be originated from an external source. In the counter, the sequence of states may follow a binary count either sequentially or at random. Since it produces a specified output pattern sequence, hence it is also known as a pattern generator.  This pattern sequence might correspond to the number of occurrences of an event or it might be well to control various portions of a digital system. The counters are classified as follows (1) Asynchronous Counter (2) Synchronous Counter Asynchronous Counter An asynchronous counter is also known as a serial or ripple counter. It is simple and straightforward in operation and construction. Usually, it requires minimum hardware. In the asynchronous 

QUINE Mccluskey Tabular Method The K-map method for obtaining simplified Boolean expression is very effective for Functions with less than or equal to four variables. For more than 4-variable logic espresso with less than t becomes any more difficult pumped to draw and solve the K-map. However, there are some general ones that are applicable to functions of a number of variables. One such procedure was originally suggested by Quine and later modified by Mc Cluskey. The Quine-Mc Cluskey method approves so as to minimize the Boolean function in the SOP and POS form. The tabular method is explained as follows. (1) Combination of minterms (a) All the minterms given in the Boolean function are expressed in the binary representation. (b) Now all the minterms are arranged in the increasing index. The index is nothing but the number of is in the binary representation of a given minterm. (c) After arranging all the minterms in various groups of indexes, the "n" index minterms will be

Single-Phase Energy Meters The single-phase energy meters are used to measure electric energy in ac. single-phase  circuit. Operating principle Of Single-Phase Energy Meters  In the single-phase energy meter, the rotation of the disk is produced by the eddy currents  due to the combined fluxes of two electromagnets. The fluxes of these two magnets are  kept 90° apart to make the rotating field. Construction Of Single-Phase Energy Meters  Figure 1.55 shows the different parts of the single-phase energy meter. It consists of a  pin-type top bearing. The side is arranged to revolve in the air gap between the poles  supply and the other with a current proportional to the main current of the circuit. The  light aluminum disc mounted on a steel spindle pivoted on a jeweled bottom bearing and  of two electromagnets, one supplied with a current proportional to the voltage of the  braking torque is produced by one or two permanent magnets inducing eddy currents in  the disc, as shown in figure

Substitution Method In the fig. 3.6 (a) the connection diagram for the substitution method for the measurement of medium resistance is shown. In this figure, R is the unknown resistance while S is the standard variable resistance "A" is an ammeter and Rh is a regulating resistance In order to connect R & S into the circuit alternatively there is a switch.   The switch is put at position 1 and resistance R is connected in the circuit The planting resistance Rh is adjusted till the promoter gives the indication of a doos scale mark.  Now the switch is thrown to the position '2' putting the standard variable resistance S in the circuit. The value of S is varied till the same deflection as was obtained with R in the circuit is obtained.  The settings of the dials of S are read. Since we substitute one resistance for another which has left the current unaltered, and it is provided that the emf of battery and the position of Ry are unaltered, the two resistances & m

Price Guard Wire Method Some form of  Price Guard Wire Method  is generally used to eliminate the errors caused by leakage currents over insulation. Fig. 3.14 illustrates the operation of This Method. In fig 3.14(a), a high resistance mounted on a piece of insulating material is measured by the ammeter voltmeter method. The micro-ammeter measures the sum of the current through the resistor (IR) and the current through the leakage path around the resistor. The measured value of resistance computed from the readings indicated on the voltmeter and the microammeter, will not be a true value but will be in error.   Figure 3.14 Application of  guard  circuit for measurement of high resistance In fig, 3.14 (b), the  guard  terminal has been added to the resistance terminal block. The  guard  terminal surrounds the resistance terminal entirely and is connected to the battery side of the micro-ammeter. The leakage current IL now

Transformer Cooling Methods When a transformer is in operation heat is generated due to I2R losses in  the windings and core losses. The removal of heat is called cooling. The following methods are generally used to cool transformers. Air Natural (AN) Cooling In a dry-type self-cooled transformer, the natural  circulation of the surrounding air is used for its cooling. The windings are protected  from mechanical injury by a sheet metal enclosure. This type of cooling is a satisfied  tory for low-voltage small transformers to a few kVA. Air Blast (AB) Cooling  The dry-type forced air-cooled transformer is  similar to that of the dry-type self-cooled transformer with the addition that continuous blast of filtered cool air is forced through the core and windings for better  cooling. The blast is produced by a fan. Oil Natural (ON) Cooling The majority of trans large rating have their windings and core immersed in oil which acts both as a cooling medium and an insulating medium. Oil-imme

Difference Between Current Transformer and potential transformer Today we Are discuss the Difference Between Current Transformer and potential transformer. The current transformer measures current and potential transformer Measure voltage.  A current transformer is similar in construction to a power transformer  that it has a magnetic circuit with a primary and a secondary winding, There is a  considerable difference in the method of operation.  In a potential transformer, the primary winding is continuously energized at a substantially constant voltage, and  the secondary is connected to a load varying in impedance within wide limits.  The  current in the primary winding is determined by the load connected to the secondary. The magnetic flux in the core is substantially constant at all loads. The  current transformer is connected in the line in series with the load. The load  determines the current through the primary. The secondary is connected to a load  or burden which does n

CURRENT TRANSFORMER  A present transformer is a gadget for the change of current from a higher incentive to lower esteem, or for the change of current at a high voltage into a proportionate current at a low voltage as for the earth potential.  Current transformers (CTs) are utilized related to air conditioning instruments, meters, or control-mechanical assembly where the current to be estimated is of such extent that the meter or instrument curl can't helpfully be made of adequate current-conveying limit. Current transformers are additionally utilized where the current is to be metered because of the trouble of giving satisfactory protection in the meter itself. In meter practice, CTs are utilized when the current to be estimated is more than 100 A. CONSTRUCTION OF THE CURRENT TRANSFORMER  The centers of CTs are normally developed with overlays of silicon steel. High-Permeability nickel steel, for example, Mumetal or Permalloy is utilized for cores where a high level of exactness i

Hopkinson Test Hopkinson Test requires two identical shunt machines which are coupled mechanically and also connected electrically in parallel. One of them acts as a motor and the other as a generator. The motor  takes its input from the supply. The mechanical output of the motor drives the generator and the electrical output of the generator is used in supplying the input to the motor. Thus, the output of each machine is fed as input  to the other. When both machines are run on full load, the input from the supply will be equal to the total losses of both machines. Hence the power input from the supply is very small. This test is also called (a) regenerative test (b) back-to-back test (c) heat-run test Hopkinson Test Circuit Diagram   The circuit diagram for the Hopkinson test is shown in Fig. 7.29 machine M is started from the supply as a motor with the help of a starter (not shown). The switch S is kept open. The field current of M is adjusted with the help of field rheostat RM

Hysteresis Motor Hysteresis motor is basically an asynchronous motor with uniform airgap and without de-excitation. This motor may operate from single-phase 3-phase supply, In a hysteresis, the motor torque is produced due to hysteresis and eddy current induced in the rotor by the action of the rotating flux of the stator windings. Stator Construction Of Hysteresis Motor The stator of a hysteresis motor is similar to that of an induction motor with the basic requirement that it produces a rotating magnetic field. Thus the stator of the motor can be connected to either single-phase supply or 3-phase supply. We know that 3-phase motors produce a more uniform rotating field than single-phase motors. For a single-phase hysteresis motor, the stator winding is of permanent split-capacitor type or of the shaded pole type for very small sizes. In the case of the permanent split-capacitor type, the capacitor should be used with an auxiliary winding in order to produce a uniform field as possibl

If an intrinsic semiconductor material is doped with an N-type impurity, not only the number of electrons increases, but the number of holes decreases below that is available in the intrinsic semiconductor. Presence of a large number of electrons increases the rate of recombination, therefore, the concentration of holes decreases. Under thermal Similarly, the concentration of holes falls below the intrinsic level for a P-type semiconductor. equilibrium, the product of the concentration of electrons (one) and concentration of holes (n) is a constant, independent of the amount of donor and acceptor doping level. This is called mass action law.

Electric Pole Types The line supports used for transmission and distribution of electric power are types including wooden poles, steel poles, R.C.C. poles, and lattice steel towers. The choice of supporting structure for a particular case depends upon the line span. The cross-sectional area, line voltage, cost, and local conditions. The different types of support described below Wooden Poles These are made of seasoned wood (sal or chair) and are suitable for lines of a moderate cross-sectional area and of relatively shorter spans, say up to 60 meters. Such supports are cheap, easily available, provide insulating properties, and, therefore, are widely used for distribution purposes in rural areas as an economic proposition. The wooden poles generally tend to rot below ground level, causing foundation failure. In order to prevent this, the portion of the pole below the ground level is impregnated with preservative compounds like creosote oil. Double pole structures of the 'A' or