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Lightning Arrester Lightning arrester devices are used at substations and at line terminations to discharge the lightning overvoltages and short-duration switching surges from lightning voltage. They are capable of discharging 10 to 20 KA of long-duration surges (8120 us) and 100 to 250 KA of the short-duration surge currents. These are non-linear resistance in series with spark gap which acts as fast switches. The requirement for Surge Arrester Lightning flashover on transmission lines can be reduced by increasing the insulation or by reducing the tower footings resistance. An alternate approach is to install transmission line surge arresters in parallel with the insulator strings to prevent insulator flashover. Following is the basic operational requirements for arresters: 1. If lightning strikes within a protected section, it should not create flashover either inside or outside the protected section. 2. If lightning strikes outside a protected section, it should not create a flashov

Ground Wire In Transmission Line A ground wire is a form of lightning protection employing a conductor well grounded at regular intervals. The protecting lines against direct strokes are by the use of overhead ground wires, This method is most generally accepted and effective.  This method of protection is known as shielding method which does not allow an arc path to form between the line conductor and ground. They are made of galvanized steel wires or AC SR conductors.  They are provided to shield the lines against direct strokes by attracting the lightning strokes to themselves rather than allowing them to strike the lines (phase conductors).  When a ground wire is struck by a direct lightning stroke, the impedance through Which the current flows is very much reduced and correspondingly higher current is required to cause flashover. For effective protection to lines against direct strokes, ground wires must requirements. (a) There should be adequate clearance between the line conduct

Expulsion type Surge Arrester Hello, friend Today we are discussing Expulsion type Surge Arrester. Expulsion type Surge Arrester is an interesting Topic So let start, It is also known as expulsion protector tube, driven tube, expulsion protective gap, or line type expulsion arrester. It is commonly used on systems operating at voltages up to 33 kV. Figure 5.1 1(a) shows the essential parts of an expulsion-type lightning arrester.  The upper electrode is connected to the rod cap and the lower electrode to the earth. Figure 5. 11(b) shows the installation of an expulsion arrester on an overhead line. Expulsion type Surge Arrester Advantage (a) They can be easily installed. Disadvantage (a) It is not suitable for the protection of expensive equipment. (b) This arrester cannot be mounted in enclosed equipment due to the discharge of gases during operation. (c) It performs only a limited number of operations.

Metal Oxide Surge Arrester Metal oxide surge arrester (MOA) which consists of a series-connected stack of discs of zinc oxide elements, operates in a very simple fashion. The methods of predicting the operation and performance of the metal oxide arresters in power system application deal with. The low current V-I characteristics of the arrester for non-adiabatic thermal behavior. The high current V-I characteristics for response to surges and system disturbances. The metal oxide technology opens many opportunities for arresters’ application in adverse operating and atmospheric conditions where gap-type arresters could not be used. It is constructed by a series connection of zinc oxide (ZnO) elements having a highly non-linear resistance. The excellent non-linear characteristic of zinc oxide element has enabled to make surge arresters without series-connected spark gaps, i.e. fully Solidstate arresters suitable for system protection up to the highest voltage. The metal oxide surge arre

Cascaded Transformer Cascade two or more transformers is desired to use for voltages higher than 400 kV. This transformer is subdivided into single units of the weight of the whole unit. Also with this, the transformer cost may be reduced and therefore transport and erection become easier. So that it is found that the cost of insulation for such voltages for a single unit becomes proportional to the square of operating voltage. Figure (2.8) shows a basic scheme for cascading three transformers. A low voltage supply is connected to the primary of the first stage transformer. Therefore a voltage is available across the secondary of this transformer. Now the excitation winding of the first stage feeds the primary winding of the second stage. The number of turns in both windings of the first stage are some. This is the same in the case of the second and third stages. Now as shown in figure (2.8) the potential of tertiary is fixed to the potential V of the secondary winding. The voltage of

History of Electric Grid The first alternating current power grid system was installed in 1886. In the 20th century, local grids time became larger as passes and were finally interconnected for economic and reliability reasons. These are delivering power to major load centers via high capacity power lines which were then branched and divided to provide power to smaller industrial and domestic users over the entire supply area. These are effective, due to efficiency, boosting features that can be cost-effective only when the stations become very large. Power stations were located strategically to be close to fossil fuel reserves. Siting of hydro-electric dams in mountain areas also strongly affected the structure of the emerging grid. Nuclear power plants were cited for the availability of cooling water. Finally, fossil fuel-fired power stations were initially very polluting and were sited as far as economically possible from population centers. In some areas, the supply of electricity,

Miniature Circuit Breakers Miniature circuit breakers are only used at LV, mainly in domestic or height-industrial or commercial applications. In general, they are used in the same application: as semienclosed or cartridge fuses and offer an alternative for protecting radial 01' ring circuits. They are usually only single-phase devices and have a typical rated load current range of up to 100 A with a maximum short-circuit rating of 16 kA at 240 V. Manually operated over-center spring operating mechanisms are used. Miniature circuit breakers usually employ a series overload coil for rapid short-circuit tripping and a bimetallic element for tripping on overloads. All miniature circuit breakers operate on the air-break principle where an is formed between the main contacts is forced, by means of an arc runner and the magnetic effects of the short-circuit currents, into metallic arc splitter plates. These cause a number of series arcs to be formed and at the same time extract energy

Air circuit breaker A circuit breaker in which the contacts open and close in the air at atmospheric pressure is known as an air circuit breaker . The principle of arc interruption followed in an air circuit breaker is different from those in any other type of circuit breaker. While both types of circuit breakers have the same objective ie. to prevent the resumption of arcing after current zero by creating a situation wherein the contact gap will withstand the system recovery voltage. In the air circuit breaker , the situation is achieved by creating an arc voltage in excess of the supply voltage. This can be done in the following way: 1. Intensive cooling of the arc plasma, so that the voltage gradient is very high. 2. Lengthening the arc path to increase the arc voltage. 3. By splitting up the area into a number of series of the arc. The principle of operation of these breakers is based on the high resistance method. They are an interruption in oil that takes place due to h

Carrier current protection Carrier current protection is the most widely used scheme for the protection of transmission lines. This protection is used for the protection of EHV and UHV Power lines. In this scheme carrier currents of the high-frequency range are transmitted and received with the help of transmission lines for protection. Carrier signal of frequency range 50 kHz to 700 kHz is used in this scheme, because below this range, the size, the cost of coupling equipment becomes high and above this range, signal attenuation and transmission loss is considerable. As the development in the power system is growing and large interconnected systems becoming very essential for high-speed protective schemes, carrier current protection is becoming suitable for EHV and UHV power lines. They are faster and superior to distance protection schemes. They are also economical and provide both primary and backup protection. In conventional time-stepped distance protection, circuit breakers at

High Voltage Schering Bridge The High Voltage  Schering bridge one in every of the most normally used AC bridge. The Schering bridge works on the principle of Equal the load on its arm. Fig. 1 shows where the specimen has been represented by a parallel combination of Rp and Cp. Let, C 1 – capacitor Which capacitance is to be determined, r 1 – a series of resistance, Indicate the loss of the capacitor C 1 . C 2 – a standard capacitor R 3  – a non-inductive resistance C 4  – a variable capacitor. R 4 – a variable non-inductive resistance At balance condition Z 1 /Z 2  = Z 3 /Z 4 Z 1 Z 4  = Z 2 Z 3 Schering Bridge is also Used To Measure Applications Are capacity and dielectric, loss measurement of all kinds of capacitances, for instance, cables, insulators, and liquid insulating materials. Dissipation Factor in Schering Bridge The dissipation factor of a capacitor is that the ratio of its resistance to its capacitive reactance. The Schering Bridge is essentially a four-arm AC bridge

Working of 3-Phase Alternator Hello, friend Today we are discussing the Working of a  3-Phase Alternator. Working on  3-Phase Alternator is an interesting Topic So let's start, The rotor winding is stimulated from the dc. exciter and alternate N and S posts are created on the rotor. When the rotor is turned the anticlockwise way by a prime mover, the stator or armature conductors are cut by the attractive transition of rotor posts. Therefore, e.m.f. is initiated in the armature conductors because of electromagnetic acceptance. The actuated e.m.f. is substituting since the N and S rotor posts alternately pass the armature conductors. The heading of instigated c.m.f. can be found by Fleming's correct hand guideline and recurrence is given by ; f=NP/120 where N = speed of the rotor in r.p.m. P = number of rotor poles Fig. demonstrates star-adjusted armature winding and d.c. field winding. At the point when the rotor is turned, a 3-stage voltage is prompted i

Construction of 3-Phase Alternator A 3-Phase alternator has 3-stage winding on the stator and a d.c. the field winding on the rotor. 1. Stator It is the stationary piece of the machine and is developed of sheet-steel overlays having openings on its inward outskirts. A 3-stage winding is put in these spaces and fills in as the armature winding of the alternator. The armature winding is constantly associated star and the unbiased is associated with the ground. 2. Rotor The rotor conveys a field winding which is provided with direct current through two slip rings by a different d.c. source. This d.c. source (called exciter) is commonly a little d.c. shunt or compound generator mounted on the pole of the alternator. Rotor development is of two types, to be specific ; (1) Salient (or anticipating) post type (2)  Non- Salient (or cylindrical) shaft type (1) Salient post type In this sort, remarkable or anticipating poles are mounted on an expansive round steel outline which

3-Phase Alternator A 3-phase alternator is a synchronous machine that changes over mechanical power into 3 control through the procedure of electromagnetic induction. A 3-Phase alternator works on the indistinguishable key rule of electromagnetic enlistment from a d.c. generator for example right when the movement interfacing a conductor changes, an e.m.f. is actuated in the conductor. Like a d.c. generator, a 3-arrange alternator similarly has a nature winding and a field winding. Review that e.m.f. incited in the armature twisting of a d.c. the generator is substituting voltage and is changed over to coordinate voltage by the commutator titted on the pole of the generator. Be that as it may, In a.c. generator or alternator, the commutator can be supplanted by a lot of slip rings and the rotating voltage produced in the armature winding can be connected to the outer burden through the slip rings. Be that as it may, essentially there is one imperative distinction between the two. In

Synchronous Generator ( Alternator) An a.c generator, commonly referred to as a  synchronous generator  or  alternator , converts mechanical power into a.c. power. The term alternator is used because it produces a.c. power. It is called a  synchronous generator  because it must be driven at synchronous speed NS (= 120 f/p)  to produce a.c. power of the desired frequency f. Thus for a 4-pole (i.e. P = 4) alternator to produce 50 Hz power, its speed of rotation must be 1500 mm (NS = 120 x 50/4 = 1500 r.p.m.). The synchronous generator can be either a single-phase or a polyphase generator. Due to many technical and economic advantages, we always produce 3-phase power and hence the need for the 3-phase alternator  (or 3-phase synchronous generator).

The voltage in India is 220 volts, alternating at 50 cycles (Hertz) every second. This is equivalent to, or like, most nations on the planet including Australia, Europe, and the UK. Be that as it may, it's unique in relation to the 110-120 volt power with 60 cycles for each second that is utilized in the United States for little machines. voltage in India The supply recurrence of Voltage in India is the equivalent all through and all power supply frameworks in India are synchronized. Be that as it may, the voltage of the intensity supply is distinctive at various stages. Recurrence 50Hz (5% resilience)- same all through the power framework. Age Voltage: 11kV(3 stage line voltage) Matrix Voltage(Long separate transmission): 132kV,220kV and 400kV, 765kV(4 Grids in India) In India there are 2 control transmission matrices, at whatever point another power station is to be set up, it must be synchronized with both of the two lattices whichever helpful. Appropriation Voltage: 33kV and

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