Its field current is switched off. The secondary output voltage will be. At full-load and 0. When the motor is delivering rated output, the slip is found to be 0. The speed of the rotor m. If it is required to deliver rated current at rated voltage and 0. Over excitation gives leading power factor and under excitation gives lagging p. To give starting torque and to maintain speed. Stepper motor works on 1-phase-ON or 2-phase —ON modes of operation. The sheath in underground cable is provided to give mechanical strength.

If the same machine is run as a motor it takes a line current of 20A from V supply. The speed of the machine as a motor will be. The number of poles of the motor are. N s will be closer to N i. A in series with main winding. B in series with auxiliary winding. C in series with both the windings. D in parallel with auxiliary winding. To make single phase motor self start. We split the phases at 90 degree. Hence, motor behaves like a two phase motor. The basic synchro unit called a synchro transmitter.

Size of conductor depends upon amount of current flow. The boundary of the protective zone is determined by the sensitivity of relay used. If the relay is more sensitive, the protective zone will be increased.

In a Potential transformer, burden should be in permissible range to maintain errorless measurement. What will be the frequency of the rotor induced emf? What is the value of emf? The Synchronous reactance of a synchronous machine is a total steady state reactance, presented to applied voltage, when rotor is running synchronously without excitation.

In a universal motor, torque pulsation is minimized by rotor and load inertia. This is defined by dielectric strength of mineral oil i. C over current relay. D directional overcurrent relay. Inverse definite minimum time lag relay characteristic is inverse but minimum time is fixed.

The operating time is inversely proportional to the magnitude of actuating quantity. A shunt branch parameters. D any of the above characteristics. Polarity test is required for parallel operation of transformers to know the direction of current flow in secondary circuit w. As shown in SCC curve the ratio of two field currents.

Universal motor has same characteristics as DC series motor and also known as an a. If torque is zero then speed may exceed up to infinite, that is dangerous for machine and machine can be damaged. Magnetic property of alloy changes with change of the temperature and. This is a special purpose machine whose stator coil can be energized by electronically switched current.

Its loss at Hz will be. As name suggests, it commutes ac into dc. The Capacity of the line is. Initially synchronous motor is operating at no load and unity power factor. When field current increases, the excitation will increase. The motor full load speed in r.

The rotor copper loss will be. This motor used single phase, 50Hz supply and stator has two windings. The number of rotor teeth for their rotor will be. In the hysterisis motor, the direction of rotation can be reversed by shifting the shaded pole region with respect to main pole.

But not by changing supply lead because it has ac supply. The charging reactance for Km length of line will be. Because load current in armature gives rise to armature mmf which react with main field mmf.

The machine has 6 poles. Reduction in the capacitance reduces starting voltage, which results in reduced starting torque. Because reversal of I a would also mean reversal of field and hence of E b.

At present level of technology, tidal power for generating electric power from sea is most advantageous because of constant availability of tidal power. The motor continues to run at the same speed because synchronous motor speed does not depend upon load, N a f. Its iron P I and copper loss P Cu are related as:. At maximum efficiency, it equals the iron loss P I which remains constant through out. Thinner the laminations, greater is the resistance offered to the induced e.

Mechanical Power developed by the rotor P m or gross power developed by rotor P g. The rotor revolves synchronously because the rotor poles magnetically lock up with the revolving stator poles of opposite polarity. Temperature of resistance furnaces can be controlled by changing either applied voltage or by number of heating elements or by circuit configuration.

The line trap unit employed in carrier current relaying offers high impedance to carrier frequency signal. Because carrier frequency range is 35 km — kHz. Equation 1 can be written as. The plus sign in Equation 2 is because of the lagging nature of current. C1 Torque production in dc machine.

C1 shows the flux density wave in the air gap and the conductor current distribution in the developed armature for one pole-pair. The force on the conductors is unidirectional. Each conductor, as it moves around with the armature, experiences a force whose time variation is a replica of the flux density B. Therefore, the average conductor force.

This force and therefore torque is constant because both the flux density wave and current distribution are fixed in space at all times. Now the torque developed is.

A lap winding is assumed here. When running at rpm it takes 30 A. Find the speed at which it will run if a 10 ohm resistance is connected in series with the armature. The armature resistance may be neglected. C2 shows a dc shunt motor. Using equation 6 of Question 2, the torque. Final variables are and. Here as flux is constant. Since torque is proportional to speed. The stator losses are 1 KW and the friction and windage losses are 2 KW. Assume that the core loss is included in friction and windage loss and the total loss under this head is 2.

Determine the speed, torque and power factor of the motor when it is connected to a V, 60 Hz, supply and is loaded to take 0. The resistance and inductance measured at the terminals of the motor are 20 ohm and 0. A When connected to a d. When connected an ac source [ Volts, 60Hz supply]. From the phasor diagram.

Assume, same flux for the same current i. The following are the test results:. Open circuit with V applied to the L. Short circuit with 20 V applied to the H. The transformer is supplying full-load secondary current at 0.

Full load secondary current. A3 Equivalent circuit referred to primary. From the short circuit test conducted on the secondary side. Resistance referred to primary. Derive also the condition for maximum torque and the expression for the maximum torque.

Fig B3 shows the per-phase exact equivalent circuit of a 3-phase induction motor. It is also known as the power across the air gap. The Power across the air gap. Electromagnetic torque developed is obtained as.

The condition that is, slip for maximum torque is obtained by equating to zero. B3 or using the approximate equivalent circuit. Equating to zero gives the slip at maximum torque as. Also substitution of s m for s in I gives the maximum torque as.

The second value On short circuit a field current of 40 A gives the full load current of A. An emf line to line of V is produced on open circuit with the same field current.

Determine the synchronous impedance. Also compute the power angle and voltage regulation at full — load 0. The occ and scc characteristics of the synchronous generator are given in Fig. Percentage voltage regulation is defined as. Calculate the two components of no-load current. If this transformer supplies a load current of 40 amp at 0. Ignore leakage impedance drop.

When the generator is loaded, the terminal voltage is V. Neglecting armature reaction, find the load current if the armature resistance is 0.

Substituting the values in the above expression. The friction and windage losses are W, the stator core loss is W and the stator copper loss is W. The rotor current and rotor resistance referred to stator are respectively A and 0. If the slip is 3. If the power factor is 0. The equivalent impedance of each transformer referred to low-voltage is 0.

The 3-phase transformer supplies a 3-phase, kVA, V, 0. Determine the minimum number of poles that the individual machines could have for this type of operation and find the shaft-speed in r. Therefore minimum requirement of poles for motor. The field current is constant; also a resistance of 1 ohm is added in series with the armature. And E b3 at twice the full load torque.

Full load torque at shaft. The transformer is operating at full-load with a power-factor of 0. Determine the voltage regulation of the transformer. Determine the voltage generated exciting emf by the machine when it is delivering full-load at 0.

Calculate the voltage regulation for rated load at 0. The respective resistance of the armature and shunt field are 0. Determine the percent reduction in the field flux required to obtain a speed of r.

The rotor emf makes complete alternations per minute. What is the input power and its power factor? V side is open circuit. It operates at a leading power factor of 0. Calculate its excitation emf. If the machine drives a load requiring a torque of Nm, calculate armature current and speed of the motor.

Now T a at no load. Put this value in equation 3. Calculate the starting torque and current when the motor is started direct on full voltage. At a certain load the motor speed is rpm and the armature current is 4. Compute the following, assuming an armature resistance of 3. The line resistance and inductance are 0. The voltage at the receiving end is required to be kept constant at 10 kV. Estimate the value of resistance which should be placed in series with it to limit the initial current to A.

Full load copper losses: Also determine the load for maximum efficiency; also compute the iron and copper losses for this maximum efficiency condition. At Full load, output at unity p. At half load, output at unity p. Differentiating above equation for maximum efficiency. Calculate the new current and power factor. The field current remaining constant, if an additional resistance of 0.

If now the armature resistance is restored back to 0. Rotational losses are W. Neglect stator copper losses. For a speed of rpm, calculate the input current, input power factor, net mechanical power output, torque and efficiency. When it is operated on load with a. The other data is: Compute i the effective armature reactance and ii maximum value of armature flux per pole.

Laboratory tests showed the following results:. Total transformer voltage drop referred to secondary. The rotational losses are watts. Using the approximate equivalent circuit, compute for a slip of 1.

Neglect ohmic resistance and determine:. The armature circuit has a resistance of 0. An external resistance of 0. For this condition compute. Open Circuit Test on L. Short Circuit Test on H. Draw the approximate equivalent circuit of the transformer referred to H.

What will be the induced e. The synchronous impedance per phase is 0. Now at leading p. At a certain load the motor speed is r. The armature terminal voltage and input are respectively V and W. The line conductors are spaced equilaterally 3m apart. The conductor resistance is 0. If the primary line current is 10A, calculate the secondary line voltage, secondary line current and output kVA for the following connections:. The turns ratio is From Fig, we find.

The armature is wave-wound and has conductors. Determine the speed at the which the motor will run and current it will draw when connected to a V supply, the total resistance of the motor being 2.

From the given data K L can be calculated as. Substituting for N in equation 4. The rotor resistance is 0.

The stator impedance may be neglected. Calculate the following quantities assuming an armature resistance of 3. The operating conditions in terms of voltage and current of the armature circuit are shown in the Fig:. The total leakage reactance is 35 ohm as referred to the primary winding. Find full load regulation at a pf of 0. Equivalent resistance of transformer referred to secondary. Determine internal power developed by the motor when it is operating at rated current and 0.

Its field resistance is ohm and armature resistance is 0. Compute the value of additional resistance required in armature circuit to reduce the speed to rpm when i load torque is proportional to speed and ii when load torque varies as the square of the speed.

Let the additional resistance required in armature current be of R ohms to reduce the speed to rpm when the load torque is proportional to speed. Determine speed, torque and power factor of the motor, when it is connected to a V, 60 Hz supply, and is loaded to take 0. The resistance and inductance measured at terminals of the machine are 20 ohm and 0. When connected to DC supply. The line resistance and inductance are respectively 0.

The voltage at the receiving end is to be kept constant at Find the sending end voltage and the voltage regulation of the line. Fig AA2 shows the phase diagram of a transformer on a load at lagging power factor and corresponds to the equivalents circuit of transformer Fig.

AA1 in which all quantities are referred to the primary. Thus is the secondary terminal voltage referred to the primary [where over bar implies a phasor]. It is seen from [Fig B1 c ] that in the generating mode, the excitation emf E f leads V t by an angle ; on the other hand in the motoring mode E f lags V t. It can be inferred from the above that, when the machine is floating, it is working neither as a generator nor as a motor and I a will be equal to zero.

The reason for this is, that at no load the machine will take that much power which is the sum of friction and windage losses. The Thevenin equivalent of an induction motor circuit model is given in Figure D1. The torque developed can be expressed as. D2 Torque-slip characteristics of induction motor with increasing values of rotor resistance. Effects of change in rotor resistance are:. A dc servomotor is often employed in a control system where an appreciable amount of shaft power is required.

These servomotors have separately excited fields. They are either armature controlled with fixed field or field controlled with fixed armature current. For example the dc servomotor [Fig. E1] used in instrument employs a fixed permanent magnetic field, and the control signal as applied to the armature terminals. The two phase ac servomotor [Fig E2] on the other hand is ideally suited for low power control applications.

The two phases are called control phase phase a and reference phase phase mthe latter being excited at a fixed magnitude of synchronous a. The motor torque gets reversed by phase reversal of the control phase voltage. E2 Control scheme for 2-phase servomotor.

The ac servomotor offers several advantages over its d. The rotor can withstand a higher temperature as it does not involve any insulation. In resistance welding a heavy current is passed through the joint to be welded and the heat caused by the resistance of the joint is sufficient to cause fusion of the metal.

Three types of resistance welding exist and they are as follows:. This method is used for welding of rods, wires or small pipes; the two ends are pressed together mechanically to form a butt joint as shown in Fig G1. For jointing two or even three sheets of metal by means of an overlapping joint, as shown in Fig G2, The sheets are held between two electrodes and current is passed between these electrodes, causing fusion at a single spot.

Where a continuous joint is required between two overlapping sheets of metal, as in constructing a tank, the two electrodes used in spot welding are replaced by two wheels between which the work travels.

However it is not advisable to make a continuous weld, as there is then a tendency for the heat gradually to build up as the welding progresses and cause burning and warping. The three different controls commonly in use are as follows:. A cam- operated switch connected in the primary circuit of the welding transformer and driven from the welding machine provides a simple device.

To overcome the difficulties encountered in the case of mechanically operated gears at high speeds, various valve-operated devices have been developed, for example, the mercury-vapour valve. With this control, current is allowed to flow until a predetermined amount of energy has been supplied to the weld. What factors control the depth of penetration of heat? Give the industrial application of this mode of heating. Induction heating processes make use of currents induced by electromagnetic action in the material to be heated.

Sufficient currents that cause effective heating can be produced only in materials of low resistivity, however it is necessary to use a magnetic field of very high frequency.

For coreless induction furnaces, the depth of penetration t is given by the formula. For normal supply frequency, with the power factor in the range 0. On the other hand the coreless induction furnace is used for the production of very high grade alloy steels; in small sizes it is widely used for work on alloys and precious metals.

In a thermal power plant heat is released in combustion of coal; this heat is used in a boiler to raise steam. Here the coal is conveyed to a mill and crushed into a fine powder, this being termed as pulverization. The pulverized coal is blown into the boiler where it mixes with the supply of air for combustion. Heat is transferred to steam pipes located in the top region of the boiler, these being initially fed with hot water from the boiler feed pump; the hot water then gets converted to steam at high temperature and pressure.

This steam is fed to the steam turbines which are the prime movers for electric generators. In a nuclear power plant binding energy of a nucleus is released by fission, which means breaking the nucleus into smaller fragments. The process of fission is carried out in a nuclear reactor. Thus the nuclear reactor is a very efficient source of energy because a small amount of fissile material produces a large amount of energy. The nuclear power plant may be sited, independently of nuclear fuel supplies, close to load centres.

However safety considerations require that these plants be normally located away from populated areas. Nuclear power plants will therefore be important sources of electrical power in future. Fig H1 shows the block diagram for a scheme of stator voltage control. This in turn will help in maintaining the field flux constant. The rectifier and inverter are rigged by means of the thyristors or GTOs or MOSFETs.

Because of its high cost, this type of control is justified only for drives wherein rugged, maintenance-free characteristics of the induction motor are essential. The sequence, as shown in the figure, is as follows:. Firstly sub-transmission lines at 66KV emanate from a transmission substation. A distribution transformer at the 66 KV substation steps down this voltage from 66KV to 11KV, that is, the primary feeder voltage.

Give its limitations also. High voltage transmission is subdivided into HVAC and HVDC transmission systems. Advantages of HVAC transmission are as follows:. As the voltage is increased, the current carried by the conductors decreases. The i 2 R losses correspondingly get reduced. However the cost of transmission towers, transformers, switches and circuit breakers rapidly increases with increase in voltage, in the upper ranges of a.

Advantages They HVDC lines are economical for bulk power transmission. The voltage regulation problem is much less in DC since only IR drop is involved. There is easy reversibality and controllability of power flow through a DC link.

Also there is considerable insulation economy. The systems are costly since installation of complicated converters and DC switchgear is expensive. The converters require considerable reactive power. Lack of HVDC circuit breakers hampers network operation. Moreover there is nothing like DC transformer; voltage transformation has to be provided on the a. This relay operates when current through it sample of power system current satisfies the condition. Such a relay is an over current relay and would operate in the shortest possible time depending upon the type of hardware employedand is called instantaneous overcurrent relay.

The phasor diagram of a directional relay is shown in Fig. Taking the leading angle as positive and defining a relay parameter as the value ofwhen the relay develops maximum torque, then. Substitution of this relation in Equn A gives. In a Nickel-Cadmium cell the positive plates are made of nickel hydroxide enclosed in finely perforated steel tubes or pockets, the electrical resistance being reduced by the addition of flakes of pure nickel or graphite. These tubes or pockets are assembled in nickelled-steel plates.

The active material in this cell is Cadmium mixed with a little iron, the latter being used to prevent caking of the active material and hence an impairment to porosity.

The electrolyte is a solution of potassium hydroxide KOH having a relative density of about 1. The electrolyte does not undergo any chemical change; hence the quantity of electrolyte can be reduced to the minimum value necessitated by adequate clearance between the plates.

The curve A in Fig M1 represents the terminal voltage of a nickel-cadmium cell during discharge at the hour rate, while curve B shows the variation for a 3-hour rate. The curve C represents the variation of the terminal voltage when the cell is charged at a rate 1. The advantages of the nickel-cadmium cell are: Methods of laying underground cables. Underground cables are generally required in urban areas where there is a high density of population.

The highest load density and the most restrictive limitations on feeder layout occur simultaneously in the central cores of major cities. Some problems associated with underground cable systems are as follows:. So there is limited room. The electrical utility must stake its claim to the routes and space allocated to it with its own duct banks.

Secondly, duct banks are needed to protect underground cable from the constant dig-ins of other utilities, stress form settling, and heat and moisture in this environment. Thirdly, digging into the street in an urban area for new additions or repairs is very expensive. Traffic control and other requirements add to cost and also digging around all the other utilities.

Summarizing, the underground urban area systems have the following characteristics. A synchronous motor with salient poles but no field winding is known as the reluctance motor.

It is used for low power, constant speed applications where special arrangements for d.

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The principle of this motor is that the stator produces a rotating field in space and the rotor is noncylindrical such that the reluctance of the magnetic path offered by the rotor to the rotating field is a function of the space angle.

Here the rotor has the tendency to align itself in the minimum reluctance position with respect to the synchronously rotating flux of the forward field. The motor is made self starting by the induction principle by providing short-circuited copper bars in the projecting parts of the rotor. In the single phase reluctance motor the rotating field can be produced by one of the phase-splitting methods. The salient pole structure is given to the rotor by removing some of the teeth of an induction motor rotor as shown in Fig M2.

The remaining teeth carry short-circuited copper bars to provide the starting induction torque. After starting, the rotor reaches near synchronous speed by induction action and is pulled into synchronism during the positive half-cycle of the sinusoidally varying synchronous torque. This would only be possible if the rotor has low inertia and the load conditions are light. The torque speed characteristic of a typical reluctance motor with induction start is given in Fig M3.

Here the starting torque is highly dependent upon the rotor position because of the projecting nature of the rotor. For satisfactory synchronous motor performance the frame size to be used must be much larger than that for normal single- phase induction motor. This accounts for the high value of starting torque shown in Fig M3. Also for reliability two smaller units in parallel are preferred. The cost of maintaining a spare is also less with two units in parallel.

For satisfactory parallel operation of transformers the following conditions have to be fulfilled:. A wrong polarity connection results in a dead short circuit. Only the transformers of the same group can be paralleled. The currents carried by the two transformers are proportional to their ratings if their p. Fig N1 shows two transformers paralleled on both sides with proper polarities but on no load.

The primary voltages V 1 and V 2 are equal. If the voltage ratios of the two transformers are not identical, the secondary voltages E 1 and E 2 though in phase will not be equal in magnitude. The difference E 1 -E 2 will appear across the switch S. When the secondaries are paralleled by closing the switch, a circulating current appears even though the secondries are not supplying any load. The circulating current will depend upon the total leakage impedance of the two transformers and also the difference in their voltage ratios.

Only a small difference in the voltage ratios will be tolerated. Division of load between transformers in parallel. It follows from the sinusoidal steady-state circuit analysis that. Selsyns or synchros are control system components which are used for transmission of small torques or motions electrically. They can be categorize into three kinds:. In the synchro-transmitter-receiver pair Fig P2 which is a single phase selsyn, the stator has three windings like the polyphase induction motor.

The rotor is similar to the rotor of a small alternator and of one winding. Fig P1 shows the cross —section of a single phase selsyn. Although it shows three stator windings, it is still a single —phase device. Two of these devices in the circuit of Fig P2 provides a system for transmission of motion. It is assumed that the generator and motor are similar units and that for the initial conditions the voltages produced on the stator of the generator by the generator rotor are equal in magnitude and 0 out of phase with those produced by the motor rotor in the motor stator.

Under these conditions the stator currents will be zero and no torque will be present in either machine. The current acting on the air gap flux will tend to restore the generator to its original position. The current will produce a torque in the motor which wil tend to cause the rotor of the motor to assume an angle corresponding to that occupied by the rotor of the generator.

The rotor of the motor therefore is an indicator of the position of the generator rotor or any device connected mechanically to it. Selsyns as position indicators: If the circuit to the rotor of the motor is opened Fig P3 a voltage will be produced in the rotor winding, the magnitude of which is a function of the angular position of the rotor of the motor w.

When the motor rotor is at a position of 90 electrical degrees from the position occupied and the rotor is electrically connected and free, the magnitude of the rotor voltage will be zero. Then any movement of the generator rotor will produce a voltage in the motor rotor which is a function of the angular position of the generator rotor or other equipment coupled to it. This circuit has found use in many servomechanism systems. For this application the motor unit serves just as a control transformer.

A third useful application of the selsyn system is that of the differential selsyn shown in Fig P4; this is constructed like a wound rotor induction motor having a 1: With the rotor of the motor locked in a particular position, a change in the position of the generator rotor will cause a corresponding change in the position of the rotor of the differential selsyn. In this way the circuit of Fig P4 performs the same function as that shown in Fig P3.

The principle of operation of a hydroelectric station can be grasped from a reference to Fig C3. C3 Principle of operation of a hydroelectric plant. From the reservoir, the water flows through the intake 1 and penstock 2 to the hydraulic turbines 3.

On flowing through the turbines where it gives up its energythe water flows through the draft tube to the tail race.

The turbine rotates fx leisure opening times christmas rotor of the generator 4.

As a result, electric current is induced in the generator stator 5. The current is conveyed via the buses 6 to the step-up transformer forex trading platform mac os x, and then to the switchgear 8.

From the switchgear, the current is directed through the power lines 9 to the loads. A hydraulic turbine is a prime mover which transforms the energy of falling water into mechanical motor trade insurance stockport of rotation and whose primary function is to forex cash multiplier reviews a water wheel hydroelectric generator.

The turbine runner and rotor of the water wheel generator are usually mounted on the same shaft, which is why the entire assembly is frequently referred to as the turbo- generator.

An impulse turbine is one in which the driving energy is supplied by the water in kinetic form; and a reaction turbine is one in which the driving energy is provided by the water partly in kinetic and partly in pressure from. The functions of the switchgear may be briefly summarized as follows.

The design and construction of the switchgear layout should be such that a reliable service is obtained under all operating conditions and in, as direct a route as possible from the alternators to the outgoing feeders.

The choice income tax on earnings abroad suitable switchgear is governed by the maximum short circuit-MVA it is called upon to deal with and also to some degree upon its relation to the system of which it forms a part.

The figure of short circuit MVA is needed for installing suitable circuit breakers. Notes on SF 6 circuit breaker. SF 6 is a heavy chemically inert noninflammable gas. Its other properties are:. As a consequence reduced electrical clearance would be sufficient. Hence it has superior arc quenching ability. With the combination of superior insulating and arc-quenching properties, SF 6 breakers have a very wide range of application The properties of SF 6 are such that the gas blast speeds need not be as high as in ABCB.

The main advantages of SF 6 circuit breakers are as follows:. An impedance relay has a characteristic given by.

If K 2 is made negative, such a relay senses impedance magnitude, and operates if the magnitude earnest money deposits california impedance seen from its location in any direction is less than a specified value. A modified impedance relay called mho relay results if a directional make fake money photoshop is restrained by voltage.

Neglecting K 4the inequality for relay operation becomes. The right hand side of Eqn 1 is a circle with centre located in the line determined by the parameter and passing through the origin as shown in Top 10 companies by market capitalization in the philippines D3.

The characteristic in this case is inherently directional. This characteristic can be alternatively expressed as. Servomotors are of two kinds, d. These are described below:. For example, the DC servomotor [Fig E3]used in instruments employs a fixed permanent magnet field, and the control signal is applied to armature terminals. The two-phase ac servomotor [Fig E4] on the other hand is ideally suited for low power control applications. The motor torque gets reversed by phase reversal of control phase voltage.

This motor has low rotor inertia and hence faster response; also it has no brushes that contact the commutator segments. To archive a low inertia, a rotor drag cup is commonly employed. High precision construction is required to maintain concentricity and to prevent any direct coupling between the two phase windings.

Pick-up from stray fields is eliminated by soft —iron shields. Induction heating is based on the principle of transformers, there is primary winding through which ac current is passed. The coil is magnetically coupled with the metal to be heated. An electric current is induced in this metal when the ac current is passed through the primary coil.

Welding is the process of joining metals of similar composition by heating to suitable temperature with or without application of pressure and addition of filter material.

The result of welding is a continuity of the homogeneous material and is of the same composition and characteristics as the parts, which are joined together. Welding process may be classified as:. The process in which the metal parts to be joined are heated options trading mp4 a plastic stage and then joined by applying external forces are known as plastic or pressure welding. The process in which the metal parts to be joined are heated to molten state and then allowed to solidify joining a localized homogeneous union of the two is known as fusion welding.

Welding process may be further classified as:. Electric resistance welding is most commonly used kind of pressure welding. It can be applied to almost any metals with in certain limits of composition. Principle of Electric Resistance Welding:. This process makes use of the heat generated by a heavy electric current passing through the materials being joined.

The electric resistance between the surface in contact being mainly responsible for the rise in temperature. The heat generated bring these surfaces to the plastic state, at this point mechanical pressure is applied to squeeze the material together thus forming the joint.

An electric arc is produced by bringing two conductors connected to a suitable source of electric current, firstly in contact and then separately by a small distance. The current continues to flow across the small gap and gives intense heat.

The heat developed is utilized to melt the part of the work piece and the filter metal and thus form the joint. So the welded joint is the union of metal parts made by localized heat without any pressure.

Principle of Arc Welding:. Current from a source ac or dc is obtained. One terminal is connected to the electrode and to other to the work piece and the circuit is completed through air gap. Due to the interruption by the air 247 binary options system electric or gas, heat is produced and the temperature how to make money at pawn shops varies from o to o C.

We also know that when the current passes through any conductor, there is loss of power in that particular conductor according to the relation, I 2 R. As the loss is proportional to the square of the current. So, when the current is reduced the drop of the voltage is less in the line, of course with the same cross sectional area of the conductor.

With the reduction of cross sectional area, considered the main advantage of transmitting electrical energy at very high voltage viz kVkV or even kV. This type of protection is used for protection of transmission lines. Carrier current frequency ranges from 35kHz to kHz are transmitted commodity futures trading india received through the transmission lines for the purpose of protection.

Each end of the line is provided with identical carrier current equipment consisting of transmitter, receiver, line — tuning download historical stock quotes into excel, master oscillator, power amplifier etc.

Thus coupling capacitor allows carrier frequency signals to enter the carrier equipment. It offers low impedance to 50Hz and high impedance to carrier frequencies. This unit prevents the high frequency signals from entering the neighboring line, and carrier currents flow only in the protected line.

Frequencies between 50 to kHz employed in different frequency bands through transmitter carrier frequencies are generated in oscillator. The oscillators can be tuned to a particular frequency selected for the application. The output of the oscillator is fed into the amplifier to overcome the losses in the transmission path george soros stock trades the transmitter and the receiver at remote end of the line.

The high frequency signals arriving from remote end are received by receiver Receiving unit comprises an attenuator, which reduces the signals to a safe value. Band pass filter, which restricts the acceptance of unwanted signals. Matching transformer or matching elements to match the impedances of line and receiving unit. Different frequencies are used in adjacent line sections. The choice of frequency bands for various sections should be coordinated. The modulator, modulates 50Hz signals and the modulated signal is fed to the amplifier and is then transmitted via coupling unit.

Compare their advantages and disadvantages. State and explain the various factors which affect the selection of an electric motor as industrial drive.

Various type of electric Drives: For dc motor control, controlled dc power from a constant voltage ac supply is obtained by means of controlled rectifiers employing thysistors and diodes.

The control of d. It gives an efficient and stepless control of dc motors. However the choppers controller requires forced commutation of thyristors which involves special thyristorized circuitry. Closed-loop control of d. Fig M14 shows a block—cum schematic diagram of a typical separately excited d.

However a shaft encoder can also be used for this purpose, and the digital output of the shaft encoder can be directly fed to the microcomputer. The armature current of the motor can be sensed by measuring the voltage across a standard resistor. M14 Block diagram of a separately excited dc drive. Till recent times variable speed drive application were dominated by d. Squirrel cage induction motor which costs approximately one — third of a d.

For control of a. These semiconductor switching cra stock option deferral transfer energy from dc supply to an a. The switching operation results in considerable harmonics in the input a. The normal power supply being of the a. A cycloconverter is a direct a.

Thus it eliminates the necessity of on intermediate d. Inspite of their stock options 83(b) election a. Cycloconverters are used for low-speed drives and controlling linear ps3 theme emma glover work from home in high-speed transportation systems.

Induction heating processes make use of currents induced by electro-magnetic action in the material to be heated. It is, however only in materials of low resistivity such as metals that sufficient currents payoneer forex partners cause effective heating can be produced. For this purpose it is often necessary to use a magnetic field of very high frequency. The core type furnace is essentially a transformer in which the charge to be heated forms the secondary circuit and is magnetically coupled to the primary by an iron-core as shown in Fig N1.

It can be seen from this figure that the magnetic coupling between the primary and the secondary is poor. Free money in nitto legends money hack electromagnetic forces cause turbulence of the molten metal which, although useful upto a point, is liable to become to severe. A crucible of inconvenient shape from metallurgical point of view is used. N2 Ajax-Wyatt Vertical Core-type Furnace.

It is known as the Ajax-Wyatt furnace [Fig N2] and uses a vertical instead of horizontal channel for the charge. The tendency of the circuit to repture due to the pinch effect is counteracted by the weight of the charge in the main body of the crucible. The circulation of molten metal is kept up round the Vee portion by convection currents and by the electromagnetic forces between the currents in the two halves of the Vee.

Such a furnace is very widely used in foundries for melting and refining brass and other not-ferrous metals. Also major breakdowns and sudden disruption of supply are avoided, thus making it a very reliable piece of electrical equipment.

It is fitted to transformers having conservator vessels and is installed in the pipeline between the transformer and its conservator tank. The relay comprises an oil tight container fitted with two internal floats which contain mercury switches connected to external alarm and tripping circuits. Normally the device is full of oil and the floats, due to their buoyancy rotate on their supports until they engage ps3 theme emma glover work from home respective stops.

The upper float gets deflected as the oil level within the relay falls and when sufficient oil has been displaced, the mercury switch contacts close, thus completing the electrical alarm circuit.

This abnormal flow of oil causes the lower floats to be deflected thus actuating the contacts of the second mercury switch and completing the tripping circuit of the transformer circuit breaker, thus disconnecting the transformer from the supply.

The arrangement for mounting the gas and oil actuated relay is shown in Fig N3. Inductive stock trades for beginners is said to occur when voltages are induced in adjacent communication lines what are amazon restricted stock units the unsymmetrically spaced power lines.

For the purpose of this discussion it is assumed that there is no neutral wire so that the conductor currents sum upto zero. This results in unbalanced receiving end voltages even when sending end voltages and line currents are balanced. Also inductive interference occurs with the adjacent communication lines.

This problem can be tackled by exchanging the positions of the conductors at regular intervals along the line such that each conductor occupies the original ruger no 1 stock set of every other conductor over an equal distance. A complete transposition cattle market prices montana is shown in Fig N5.

This arrangement causes each conductor to have the same average inductance over the transposition cycle. It can be shown that over the length of one transposition cycle, the total flux linkages and hence the net voltage induced in a nearby telephone line is zero and also that the power line transposition is ineffective in reducing the induced telephone line voltage.

These harmonic line currents are undesirable because:. Another feature is that with unbalanced power line transposition apart from being ineffective, introduces mechanical and insulation problems.

It is therefore easier to eliminate induced voltages by transposing the telephone lines instead. Some induced voltage will always be present on a telephone line running parallel to a power line because in actual practice transposition is never completely symmetrical. Therefore when the lines run parallel over a considerable length, it is a good practice to transpose both power and telephone lines.

The two transposition cara membaca candlestick pada trading forex are staggered and the telephone line is transposed over shorter lengths compared to the power bullish reversal patterns forex. From figure, flux increases from its zero value to maximum value F m in one quarter of the cycle i.

Rate of change of flux per turn means induced emf in volts. If flux F varies sinusoidally, then rms value of induced emf is obtained by multiplying the average value with form factor.

A universal motor develops unidirectional torque regardless of whether they operate on DC or AC supply. The production of unidirectional torque when the motor runs on AC supply can be understood from the above figures. The motor works on the same principle as a DC motor i. This is true regardless of whether the current is alternating or direct. The rotor is same in construction to that of a DC motor but the stator is laminated necessarily because the flux is alternating when the motor is operated from AC supply.

Stepper motor consists of a slotted stator equipped with two or more individual coils and a rotor structure that carries no winding. The classification of the stepper motor is determined by how the rotor is designed. If the rotor is made up of a permanent magnet, it is called a PM stepper motor. If no magnet exists on the rotor only a rotor core it is called a reluctance type stepper binaryoptions.net review. The presence of the permanent magnet in the rotor furnishes the motor with the equivalent of a constant DC excitation.

The elementary operation of a four phase stepping motor with a 2-pole rotor is explained below. Major advantage of using stepper motors is that no feedback is required from the rotor to ascertain the angular position of rotor. The transfer of energy from stator to the rotor of an induction motor takes place entirely inductively with the help of flux mutually linking the two. Hence an induction motor is essentially a transformer with stator forming the primary and rotor forming the rotating secondary.

Variable Frequency Operation of Transformer. For power transformers frequency response is of no serious interest because these units are operated at a single fixed frequency. Frequency response is to be studied in communication circuits where the frequency of source voltage is likely to vary. At low frequency x j is a small, which causes a severe drop off of voltage by shunting the fixed load impedance.

At intermediate frequency, x 1 and x 2 are quite small while x j is sufficiently large that it may be omitted. For a resistive load the equivalent circuit consists of solely resistive elements so that the transfer function remains constant over the band of intermediate frequencies. However x j may be omitted.

As the frequency increases the drop across x 1 and x 2 increases thereby causing a dip in the output voltage.

Therefore the gain drops off as frequency increases. Armature reaction is the effect of magnetic field setup by armature current on the distribution of flux under main poles of a generator. The armature reaction has two effects. Demagnetization- reduces the generated voltage and torque. Cross magnetization — distorts the field and causes sparking at brushes.

Fig a How to make a living with binary options bullet mq4 b. When only I F is present the, mmf is perpendicular to MNA Figure a. When only armature current is present, mmf is along the MNA. When the machine is actually working, the resultant mmf vector is at an angle form MNA. This causes the brushes to be shifted to a new MNA perpendicular to resultant elul 29 stock market. Now at this new MNA, mmf of I a is along new MNA.

This mmf is bike market rostock innenstadt into two component F d and F c which are demagnetizing and cross magnetizing mmf respectively. An AC Servomotor is basically a two-phase induction motor except for certain special design features.

A two phase induction motor consists of two stator windings oriented at 90 o. Voltages of equal magnitude and 90 o phase difference are applied to two stator phases, thus making their respective fields 90 o apart in both time and space skype stock market trading for beginners in a constant magnitude RMF.

The direction of rotation depends upon phase relationship of voltages V1 and V2. The rotor is a short-circuited one producing torque in direction of field rotation. The torque speed characteristic is shown in the Fig. It has either the conventional split phase stator and a centrifugal switch for cutting out the auxiliary winding after startup.

The squirrel cage type rotor is of unsymmetrical magnetic construction. The rotor offers variable magnetic reluctance to the stator flux, the reluctance varying with the position of the rotor.

The basic operating principle is that when a magnetic piece of hillary clinton stock market is located in a magnetic field a force acts on the material, tending to bring it into the densest portion of the field.

The force tends to align the specimen of material in such a way that the reluctance of the magnetic path that lies trough the material will be minimum. When the stator winding is energized the revolving magnetic field exerts reluctance torque on the unsymmetrical rotor tending to align the salient pole axis of the rotor with axis of the RMF due to minimum reluctance.

If the reluctance torque is sufficient to start the motor and its load, the rotor will pull into step with the rotating field and to run at the speed of the revolving field. The switched reluctance machine is a special variation of the simple reluctance machine that relies on continuous switching of currents in the stator to guarantee motion of the rotor.

It is also a true reluctance machine in that it has salient poles both in rotor and in the stator. State its advantages over other methods of heating. Electric heat is provided by use of a high temperature wire, which is resistant to electric flow with more heat being produced by more electric current being fed into the heating element, creating more resistance and more heat.

This stock commission fees tax deductible of producing heat is called electric heating. Uniform and economic heating capability. Resistance welding is a process used to join metallic parts with electric current. In all forms of resistance welding, the parts are locally heated until a molten pool forms. These parts are then allowed to cool and the pool freezes to form a weld nugget.

To create heat electric current is passed through work pieces. The heat generated depends on the resistance and thermal stock market graphs historical of the metal and the time for which the electric current is applied.

The heat is expressed by the equation. Advantage of Nuclear Power Plants. Nuclear Power station reduces the demand for oil coal and gases. Weight of nuclear fuel required for a given station capacity is negligible compared to that required for a conventional thermal power station.

As a result the problems of transport and resulting costs are avoided. The area and volume need for a nuclear power station is less in comparison to a conventional power plant of equal capacity. In addition to producing large amount of power, making money rs eoc nuclear power plant produces valuable fissile material, which is extracted when the fuel is renewed.

Can it be negative also? The ratio of receiving end power to the sending end power of a transmission line is known as the transmission efficiency of the line. The difference in the voltage at the receiving end of a transmission line between the conditions of no load and full load is called voltage regulation and is expressed as a percentage of the receiving end voltage.

When the pf is leading, and the term IX sin f R is 95 binary options signals australia than the I R cos f Rthen the voltage regulation becomes —ve.

In this system separate feeders radiate from a single sub station and feed the distributors at one end only. Figure shows a single line diagram of a radial system for a DC distribution where a feeder OC supplies a distributor AB at a point A. Obviously the distributor is fed at one end only i. The radial system is employed only when power generated at low voltage and sub-station is located at the center of the load.

In this system the primaries of distribution transformers form a loop. The loop circuit starts from the sub-station bus bars, makes a loop through the area to be served and returns to the sub-station. The sub-station supplies to the closed feeder LMOPQRS. The distributors are tapped from different points M, O, and Q of the feeder through distribution transformer. This system has the advantage of continuity of supply and less voltage fluctuations.

When the introducer broker instaforex ring is energized by two or more than two generating stations or substations it is called inter connected system.

In the above diagram of the inter-connected system the closed feeder ring ABCD is supplied by two sub stations S 1 and S 2 at D drips stock market C.

Inter connected system has the advantages of increased service reliability and increasing efficiency of the system by reducing reserve power capacity. Any motor with a speed control arrangement can be termed as a drive.

Both AC and DC are used for electric drives. There are two types of drives viz, group drive and individual drive. Each machine having its own driving motor is called individual drive.

Selection of the type drive depends on the application to be served. This method of laying UG cables is simple how to buy penny shares in south africa cheap. In this method a trench is dug. The trench is covered with a layer of fine sand and the cable is laid over the sand bed.

The sand bed prevents the entry of moisture from the ground and thus protects the cable from decay. After the cable is laid, it is then covered with bricks and other material to protect the cable from mechanical injury. In this method, conduit or duct of glazed stone or cast iron or concrete convergys work at home agent reviews laid in the ground with manholes at suitable positions.

The cables are then pulled into position from manholes. Figure shows section through four way underground duct line. Three of the ducts carry information cables and fourth duct carries relay protection connection, pilot wires. Care must be bombay stock market chart that where the duct line changes the direction, depths, dips and offsets are made with a very long radius or it will be difficult to pull a very large cable between manholes.

In this method of laying the cable is laid in open pipes or troughs dug out in earth along the cable route. The troughing is of iron, stone ware, asphalt or treated wood. After the cable is laid in position, the troughing is filled with a bituminous or asphaltic compound and covered. Cables laid in this manner are usually plain lead covered because troughing affords good mechanical protection.

On long lines carrier pilot relaying is cheap and more reliable than the pilot wire relaying even though it is expensive and complicated than with pilot wire relaying. In this type of protection the phase angle between two ends of the line decides whether the fault is internal binary options pending order external. Each carrier current receiver receives carrier current from its local transmitter as well as from the transmitter at the other end of the line.

These signal are then compared for any fault condition and action is taken correspondingly. Traps are used to confine the carrier currents to the protected section so as to avoid triple binary options from other carrier current channels. According to working principle of the transformer, it works on Faraday laws of Electromagnetic Induction.

The changing rate of magnetic flux is responsible for e. But in case of dc supply system d. Therefore, we can not use transformer for dc supply system. Where are the salient-pole type of synchronous machines used? It has large number of projecting salient poles having their cores bolted or dovetailed on to a heavy magnetic wheel of cast iron or steel of good magnetic qualities.

The rotor consists of a smooth hedging in stock market forged steel cylinder having a number of slots milled out at intervals along the outer periphery parallel valuation techniques discounted cash flow earnings quality measures of shaft for accommodating field coils.

Such machines are characterized by their large diameter and short axial length. These machines are characterized by their small diameter and large axial length. It is used for low and medium speed synchronous machines. It is used for High speed synchronous machines. Armature reaction means acuity stock brokers sri lanka on magnetic field distribution, this works in two ways:.

The first effect leads to reduce the speed of dc motor and second to produce sparking at brushes. For armature reaction illustration, two poles have been considered and initially assumed that there is no current in the armature conductors.

The assumptions are as under:. A coincides with the geometrical neutral axis G. Induction Generator is a machine similar to a induction motor and driven above synchronous speed.

Therefore, this is acting as an ac asynchronous generator. The magnetic flux in typical pulse transformer does not change between positive and negative values. The typical pulse Transformer operates in unipolar mode. A fixed dc current can be used to create biasing, a dc magnetic field in the transformer core thereby, forcing the field to cross over the zero line. The pulse transformers usually operate at high frequency necessitating use of low cores.

The circuit treats parasitic elements, leakage inductance and winding capacitance make money as a ticket broker lumped circuit elements. But they are actually distributed elements.

The pulse transformer design usually seeks to minimize voltage droprise time and pulse distortion. Voltage drop declines output pulse voltage over the duration of one pulse.

It is caused by the magnetizing current increasing during the time duration of the pulse. The pulse transformer can be divided into two major types:. These are used in precise control of heating element from dc voltage source.

These are used for delivery how the stock market affects the economy signal at output. The transformers deliver pulse like signal or series of pulses. The turns ratio of pulse Transformer can be used to adjust signal amplitude and provide impedance matching between source and load. Signal pulses Transformer are frequently used in communication systems and digital network.

This motor is similar to a 3-phase induction motor except its stator is provided with a single phase winding and a centrifugal switch is used in some types of motors, in order to cut out a winding used only for starting purpose.

This motor has distributed stator winding and squirrel cage rotor. When stator is fed from single phase supply, its stator winding produces a flux which is only alternating.

This alternating or pulsating flux acting on a stationary squirrel cage rotor cannot produce rotation only a revolving field can. Therefore, single phase motors are not self-started. If the rotor of single phase induction motor is initially started by hand or otherwise, in either direction, then immediately a torque arises and motor accelerates to its final speed. An alternating uniaxial quantity can be represented by two oppsitely rotating vectors of half magnitude.

To make single phase induction motor self starting, it is temporarily converted into a two phase motor during starting period. For this purpose, the stator of a single phase motor cotatii forex gratuite provided with an extra winding known as starting winding. Two windings are spaced at 90 0 electrically apart and connected in parallel across single nine sectors stock market supply.

In special cases, HVDC line is preffered. Larger industries receive power at kV and internal distribution at 3. It is disconnecting switch to disconnect the system from line parts under no load condition. This is used to discharge the voltage on the lines to earth after disconnecting them. This is used to divert the high voltage surge to earth and maintaining continuity during normal voltage. To step down the current for measurement, protection and control purposes.

To step down the voltage for the purpose of protection, measurement and control. Switching OFF during abnormal conditions to interrupt the fault current. A short length wire having low melting point, connected in series with circuit.

In the event of fault, the circuit current rises abruptly and fuse wire melts to interrupt the circuit. The switches are specified as per voltage rating, current rating, number of poles, duty cycle and fault interruption capacity. Classification of secondary Cells.

Secondary cell is one in which chemical reaction is reversible. Therefore, secondary cell can be recharged after use. These cells are also known as storage cells and accumulators.

These cells are classified as follows: Lead acid cells are used in electric substation for emergency lighting, to provide d. Ni — cadmium Alkaline cells of higher capacity and lower weight are preferred. These cells have longer life, lower running cost and less maintenance. Give examples of their applications and explain their features.

Solid State controllers Vs Conventional Controllers: Primarly motor control circuit of conventional type consists of switches, fuses, relays, contactors and associating cabling. This type of conventional contactor control system become bulky if implemented for complicated logic. The trouble shooting also becomes difficult and time consuming. A PLC Programmable Logic Controller is known as solid state controller. The main difference between relay logic controller and computer based solid state controller PLC are: In computer based system, it is easy to change program through software.

It avoids lot of external control wiring. The PLC consists of: A PLC work is based on continuous scanning program. It has three steps. This is a single phase special purpose motor. Its hysteresis torque remains constant from locked rotor to synchronous speed. It has no winding. The rotor poles are magnetically locked up with revolving stator poles of opposite polarity.

The mechanical power developed in a hysteresis motor:. These motors are useful for driving tape- decks, turn table and other precision audio equipments. The commercial motors have two poles, they run at 3, rpm at 50 Hzsingle phase supply. The HVDC transmission is selected as an alternative to extra high voltage AC transmission system due to following reasons:.

In HVDC link, AC power is converted by power electronic device at one end. The energy is transmitted in HVDC form to the other end. At the other end the DC power is inverted and fed into receiving A. HVDC transmission system has a HVDC converter substation at each end and HVDC transmission line in between. These cells are compact in size and have long life. Examples of button cells are Mercury oxide and silver oxide cells. Mercury oxide cells have Mercury cathode and zinc as a anode.

The watch battery are usually single cell with nominal voltage between 1. The specific feature of button cells:. Magnese oxide, silver oxide, carbon monoflouride, copper oxide.

Alkali or organic, alkali required for zinc cathode and organic for lithum cathode. Voltage in long transmission lines varies greatly at the end when large inductive load are present and when inductive load disconnected suddenly, the voltage tends to rise considerably above its normal value because of line capacitance. Therefore, by installing a synchronous motor with field regulator, the voltage rise can be controlled.

Speed control of D. C Motors Shunt type. C shunt motor speed can be controlled by the following methods:. The flux of DC motor can be changed by changing the field current with the help of shunt field rheostat. Shunt field of motor is connected permanently to a fixed exciting voltage, but armature is supplied with different voltages by connecting it across one of the several different voltage by means of suitable switchgear.

Starters for three phase induction motors: Certain conditions must be satisfied in order to avoid any local circulating currents and to ensure that the transformers share the common load in proportion to their kVA ratings, The conditions are:. The speed control of induction motor is obtained by various methods:. A slip ring wound motor is an adjustable speed motor. The rotor winding terminals are connected to slip rings.

A 3- F star connected rheostat is provided separately with motor. By changing the resistance in rotor circuit, the torque speed characteristics of machine can be changed. The speed reduces in slip ring induction motor through rheostat control; and this can be obtained only if the motor is loaded under no load condition.

The no-load speed changes are very little with the variation in the load resistance. The squirrel cage induction motor with single or double pole changing windings are available as follows:.

Machine Tools, lathes, boring mills, drill, planers.

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The Multi-speed motors are of slip ring type used for hoist, conveyor and elevator. The interconnection of hydro and thermal power generation plant or reuse of waste product of first generator as a fuel of second generator or other machine:. The large power system comprising several power stations load centres interconnected to form a single grid operation of such a grid is controlled from a load centre or load dispatch centre.

The national load control centre is linked with various regional despatching stations. The regional load centres send commands from power stations to control room periodically by telemetric data transmission system. But setting of the governor for turbine is changed according to instruction of regional control centres. Therefore, The input of turbine from governor gets automatically adjusted by primary load frequency control and frequency is maintained.

The governor setting is determined by economy load dispatch instructions from regional load control centres. The total load cogeneration control is achieved by:.

These are used in medium power plants upto 25MW for industrial and marine applications. Generators are usually gear driven to speeds of to rpm for 50 Hz. Diesel engines have a speed range of rpm to rpm higher speed for gas turbine driven set. The critical speed and torsional or natural frequencies are checked for diesel generator set to avoid resonance.

Brushless excitation is commonly used. The diesel generators are mounted on same bed plate of prime mover. The protective relaying senses the abnormal conditions as a part of the power system and gives an alarm or isolate that part from the healthy system. The relays are compact, self-contained devices, which respond to abnormal conditions. Whenever abnormal conditions occur, the relay close its contacts. Thereby trip circuit of the circuit breaker is closed and circuit breaker will open.

So that, the faulty part will be disconnected from the supply. It is the time between fault instant and closing of relay. A rapid contact fault cleaning i. Therefore, relay time must be minimum as much as possible i. It refer to the smallest value of actuating quantity at which protection starts operating in relation with the minimum value of fault current in the protection zone. Minimum short circuit current. Minimum operating current in protection.

A quality of protective system by the virtue of whichthe protective system remains operating and stable under certain specified conditions such as system disturbances, through faults, transient etc. The protective relaying should not fail to operate in the event of faults in protected zone. The adequateness of protection is judged by considering following aspects:. Mostly used in transmission system due to effective voltage upto kV. Less skilled staff is required. Less light giving thus.

Chances of frequent failure due disturbance from other system. Highly skilled staff is required. How is it caused and what steps are necessary to reduce its effect? A welding process is required to join two metal parts by heating them to melting point. Electrical welding is used for joining of fabricating structures, machinery parts, pipes, bus bars, bridges, ships railway bogies etc. Electrical welding has two distinct types:.

In resistance welding the current is passed through the joint to be welded and the heat is caused by I 2 R losses in the joint, melting of metal and subsequent welding under pressure between faces to be welded. The heat is produced by the arc struck between the welding electrode and the metal to be welded. Pressure is not applied between faces to be welded. Inductive interference depends upon gradient of voltage at surface of conductor or corona. The inductive reactance is affected from conductor attenuation at KHz and varies from 0.

Motor used in ceiling fan: Single phase induction motor is used for ceiling fan; this motor is more or less similar to polyphase induction motor, except that. When single phase supply is fed, its stator winding produces a flux or field which is only alternating i. It is not a synchronously revolving or rotating flux, as in the case of a two or three phase stator winding fed from 2 or 3 phase supply.

Now, an alternating or pulsating flux acting on stationary squirrel cage rotor can not produce rotation only revolving flux can.

Therefore, single phase is not self-starting. To make single phase induction motor self starting the following method is adopted. In this method, phase is split by introducing a resistance and a switch in starting winding and both windings are connected in parallel with supply. Capacitor — Start induction run motor: The necessary phase difference between I S and I m is produced by connecting a capacitor in series with starting winding.

The capacitor is designed for short duty service. A tachometer generator has rotating magnet, which may be permanent magnet or electromagnet. The rotation of magnet causes an emf to be induced in stator.

The amplitude and frequency of this e. So that, output voltage of AC tachometer generator is rectified and is measured with a PMMC instrument. This can be achieved by following ways. The carrier current protection scheme is used for protection of transmission lines. The carrier current of frequency range 30 to KH Z or 80 to KH Z and received through the transmission lines for the purpose of protection.

In this system, each end of the line is provided with identical carrier current equipment consisting of a transmitter, receiver, line tuning unit, master oscillator, power amplifier etc. Power angle characteristics of a synchronous machine: The power transferred by a synchronous machine. An active power generated by a synchronous generator or consumed by synchronous motor is given by following equation: The power output of a synchronous machine can be changed only by changing its power output.

Change in excitation does not change in power output. The change in excitation will give only change in e. When motor is at rest, no back emf will develop in armature. Now, if full supply voltage is applied to stationary armature, it will draw very large current because armature resistance is relatively very small. This excessive current is large and this will damage commutator, brushes etc. To avoid this situation, a resistance is introduced in series with the armature for short duration with the help of starter, which limit the starting current to safe value.

The starting resistance is gradually cut off and motor gets full speed with back e. However, very small motor can be started from rest by connecting directly to supply These motors have relatively large armature resistance than larger motors.

These small motors also have low value of inertia. When stationary coils are supplied with 3 phase supply, a uniform rotating magnetic field of constant value is produced. The flux due to current flowing in each phase winding is assumed sinusoidal and is represented in figure b The direction of fluxes are shown in Fig. Calculation of f r:.

Adding above equationswe get. Therefore, resultant flux is of constant magnitude and does not change with time t. Usually, the shaded pole principle is employed for hystersis motor. The rotor of this motor is smooth, having high retentively, so that, hystersis loss is high.

It has no winding, the rotor poles magnetically locked up with the revolving stator poles of opposite polarity. The mechanical power developed by rotor is given by. Power System structure with diagram:. Electrical power system can be divided into following regions:. In all these regions, there are switchgears.

Bus bars are connecting bars to which a number of local feeders are connected. Bus bars operate at constant voltage. Besides the bus bars, there are other equipment in the electrical schemes such as circuit breakers, CTs, PTs, etc. These equipments can be installed according to various schemes depending upon requirements.

Equipment in electrical scheme of Transmission system. The power transformers are installed between two bus bars of different voltage levels. A power transformer is the costliest, heaviest, and most important equipment in substation. Typical station is distribution system. In 11 kV distribution system, the cost of elaborate protection may not be justified for protection transformer upto about kVA. The substations are generally unattended. V fuses is the only protection provided on H.

The switch gear is installed in the substation of local points, such as industrial works, railway substation, cinema house, large building, foundries etc.

The substation has following items:. The periodic rise and fall of water level of the sea can be used to convert wave energy into electrical energy by moving turbine blades from fall and rise of water waves. The rise and fall of wave follow sinusoidal curve. This plant is of mW capacity. There are three main components of a wave energy power plant as follows:. The turbines, electric generators and other auxiliary equipments are the main equipments of power house.

The conversion of solar energy stored as heat in the ocean into electrical energy by making use of the temperature difference between warm surface water and the colder deep water. The operation of OTEC ocean Thermal energy conversion plants is based on a well-established physical Thermo- dynamics principle.

If a heat some is available at a higher temperature and a heat sink at a lower temperature, it is possible in principle to utilize the temperature difference in a machine or prime moves Turbine that can convert the part of the heat taken up from sources into mechanical energy and hence into electrical energy.

Factors involved in circuit breaker rating. The following rated quantities for HV ac circuit breeders. The time interval between energizing of closing circuit and contact touch with all poles. Time between energizing of shunt trip release and contact toad in all poles. Time between contact touch in first pole and separation of arcing contact in all poles during close open operation. The rated characteristics of circuit breaker include rated normal current, rated voltage, rated insulation level, rated transient recovery voltage, rated short circuit breaking current, rated short circuit making current, rated operation sequence etc.

Factors involved in selection of factory drives: High starting torque, Hazardous location. Duty cycle, noise level, load characteristics etc. Core or iron losses: Core flux in transformer remains constant for all load. These losses are due to ohmic resistance of transformer windings. Synchronous reactance determination of a synchronous machine.

The drop in voltage due to armature reaction may be accounted by assuming the presence of a fictitious reactance X a in the armature winding. The leakage reactance X L or X P and the armature reactance Xa may be combined to give synchronous reactance Xs.

The flux of d. This method is used when speeds below the no load are required. As supply voltage is constant, the voltage across the armature is varied by inserting a variable resistance in series with the armature circuit. For load of constant torque, the speed is approximately proportional to the potential drop across the armature. Here shunt field of motor is connected permanently to a fixed exciting voltage, but armature is supplied with different voltages by connecting it across one of the several different voltages by means of suitable switchgear.

This system is used for wide range of speed control i. By applying variable voltage across its armature, any desired speed can be obtained. This variable voltage is supplied by a motor-generator set which consists of either d. In practice it is impossible for an induction motor to run at synchronous speed, due to friction and windage losses. Therefore, induction motor runs at synchronous speed by another machine, which supplies the friction and windage losses. In this case, the above circuit behaves like an open circuit.

These values are used to described model Induction Motor. In this case rotor is locked or allowed very slow rotation and rotor windings are short circuited at step rings.

Torque developed by a single phase induction motor depends on its speed. But relationship can not be represented by simple equation. This is called breakdown Torque. At full load, the motor runs at a speed of N. As long as the torques are in balance, the motor will run at constant speed but lower speed. If the load torque exceeds to 2. Important advantages of HVDC transmission: The primary protection is essential protection provided for protecting a machine.

The primary protection is the first to act and back-up protection is the next in the line of defence. Therefore, if primary protection fails, the back-up protection comes into action and removes the faulty part from one healthy system. When main protection is inoperative for purpose of maintenance, testing etc.

The back-up protection acts like main protection. The back up protection can be classified as:. Same circuit breaker is used by both main and back-up protection, but protective systems are different. Separate trip coils may be provided for the same-breaker.

Different breakers are provided for main and back up protection, both the breakers are being in the same station. Here system is having central control and it can be provided with centrally controlled back-up. The central coordinating station receives information about the abnormal conditions through high frequency carrier signals.

The stored programme in digital computer determines the correct switching operation as regard severity of faults, system stability etc. Main protection at various stations and back-up protection for all stations is at central control centre. The coreless furnace consists of a crucible formed from a refractory material, which contains the charge to be melted. This crucible is surrounded by a helical induction coil also called inductor through which the alternating current flows. The heavy currents are introduced in the charge by transformer action.

The heat results from I 2 R effect within the charge. The advantages of induction furnaces, in general, include faster and efficient melting, relatively low melting cost. Higher temperature can be attained, can be used for temperature holding etc. The induction furnaces are used for melting, temperature holding, and super heating purposes.

The differential relay responds to vector difference between two or more similar quantities. Differential protection is generally a unit protection. The protected zone is exactly determined by location of CTs. The vector difference is achieved by suitable connection of CT or PT secondaries. The inductive reactance affected from conductor attenuation at kHz varies from 0. Nickel cadmium cells employ a solution of potassium hydroxide in distilled water as electrolyte with a specific gravity of 1.

NiOH and specially treated graphite. Cadmium oxide or iron oxide. No finishing rate is needed. The voltage of charger should not be above 1. Main components of thermal power plants are: Heat generated in the furnace is utilized to covert water into steam. Engine or turbine to use the heat energy of steam and perform work. The steam produced inside boiler is nearly saturated. This steam as such should not be used in the turbine because the dryness fraction of the steam-leaving boiler will be low.

This results in the presence of moisture, which causes corrosion of turbine blades etc. Therefore, to rise the temperature of steam, super heater is used. It consists of several tube circuits in parallel with one or more return bends connected between headers.

Super heater tube range is from 1 to 2 inch in diameter. Steam condenser is required to receive the exhaust steam from the turbine or engine to condense it and maintain a pressure of the exhaust lower than atmospheric. This improves the efficiency of the plant. Air inside the condenser should be pumped out continuously in order to maintain vacuum.

The condensation of steam occurs in the range of 25 0 C to 38 0 C. Construction of lead acid cell and process of charging and discharging of cell: A lead acid type batteries are known as secondary battery or cell, which can be charged for reuse.

This cell has following components:. It consist lead peroxide deposited on grid frame of antimony lead alloy. It consists of porous-spongy lead pasted on grid frame.

Sulphuric acid is an electrolyte. These are thin porous sheet suspended between positive and negative electrode to prevent short circuit. These are made of nickel plated copper alloy. It contains all plates, electrolyte, separators, vent plug, cell connectors and battery terminals. It is made of hard rubber. These are used to connect a number of cells of same type either negative or positive in series so as to provide required voltage. Connect dc supply to electrodes with corresponding polarity.

The direction of current now opposite to that in discharging process. The current flow from external dc source to positive electrode to negative electrode through the electrolyte and back to the source. This process results in rise in cell voltage 2 or 2. The reaction taking on electrodes are:. When cell is fully charged anode is PbO 2 and cathode is Pb. An external load is connected to electrodes of cell, therefore, an electric current flows in load. The process is known as discharging. A fully discharge cell has a voltage 1.

The reaction-taking places at electrodes are. The network of transmission lines is formed by three phase AC system. This is required for Bulk power transfer from large group of generating stations to main transmission network.

Short power transmission line:. These lines are required to carry power from main sub-station to local distribution area. Further power supply is distributed through pole mounted sub- station or plinth mounted sub-station.

Medium power transmission line: Medium distance power transmission line has voltage range kV. These lines supply power directly to big organization or industry, which establishes own sub-station. Long power transmission line. A long distance power transmission line has voltage range kV to kV.

These lines are used for transfer of power from sending end to receiving end or for system inter- connection for exchange of power between independently controlled networks. Higher voltage gives lesser current, lesser I 2 R losses, higher power transferability. Schematic diagram of directional over current relay with its working: The directional over current protection comprises over current relay and power directional relay in a single relay casing.

The power directional relay does not measure the power but it is arranged to respond the direction of power flow. The directional operation of relay is used where the selectivity can be achieved by directional relaying.

The directional relay recognizes the direction in which fault occur relative to the location of relay. It is set such that it will actuate for fault occurring in one direction only.

It does not act for faults occurring in the other directions. In above diagram consider a feeder AB phasing through subsection 1.

The circuit breaker in feeder 1B is provided with a directional relay R, which will trip the CB, if fault power flow in direction 1B alone. Therefore, for faults in feeder 1A, the CB does not trip unnecessarily. However, for faults in feeder 1B, CB B trips. The choice of transmission systems and rated voltages for a transmission line is made from HV AC upto kV EHV AC kV — kV UHVAC above kV AC depending upon technical and economic consideration.

In case of very long lines of above km, intermediate switching sub-stations are necessary to install the shunt reactors for compensation. In some cases of big cities, industrial localities, it is impossible to acquire right of way for EHV AC lines.

The creep age distance leakage distance determined on the basis of required impulse with stand level. The critical value of voltage stress depends upon pressure, temperature, humidity, pollution level in air. In this motor, necessary phase difference between I S and I m is produced by connecting a capacitor in series with the starting winding as shown in above figure.

The capacitor is generally electrolyte type and mounted on the outside of the motor. This capacitor is designed for extremely short duty service and is guaranteed for not more than 20 periods of operation per hour, each period not to exceed 3 seconds. Thus leaving only the running winding. This type of motor has either conventional split phase stator and a centrifugal switch for cutting off auxiliary winding or a stator similar to that of permanent split capacitor run motor.

The stator produces resolving field. The working of this motor is that when a piece of magnetic material is located in a magnetic field, a force acts on the material, tending to bring it into the most dense portion of a field.

The force tends to align the specimen of material in such a way that the reluctance of the magnetic paths that lies through the material will be minimum.

When stator winding is energized, the revolving magnetic field exerts reluctance torque on the unsymmetrical rotor tending to align the salient pole axis of the rotor with the axis of resolving magnetic field. If the reluctance torque is sufficient to start the motor and its load, the rotor will pull into step with the revolving field and continue to run at speed of revolving field. However, rotor poles lag behind stator poles by certain angle known as torque angle. The constant speed characteristic of a reluctance motor makes it very suitable for signaling devices, recording instruments, timers, phonograph etc.

This motor rotate through a fixed angular step in response to each input current pulse received by its controller. These motors used for precise positioning of an object or precise control of speed without using closed loop feed back.

The unique feature of this motor is that its output shaft rotates in series of discrete angular interval or steps, one step being taken each time a command pulse in received. When a definite number of pulses are supplied, the shaft turns through a definite known angle.

So that the motor is well suited for open loop position control because no feed back is taken from output shaft. These motors develop torques ranging from 1 MN upto 40 N-m in a motor of 15 cm diameter suitable for machine tool applications. Their power output ranges from about 1 W to Max of W. The moving part in stepper motor is its rotor which has no winding, commutator or brushes.

Therefore, the motor is quite robust and reliable. Deduce an expression for the load shared by the two transformers in parallel when the transformers have equal voltage ratio. Condition for parallel operation of single phase Transformer: State the various applications of synchronous motor.

Important functions of damper winding in a synchronous motor: Various applications of synchronous motor: Hence, it can be used for power factor correction purpose. Variable frequency drives with synchronous motors are used for speed control. The DC shunt generator runs at constant speed and some emf will be generated due to residual magnetism in the main poles.

This process will continue and generator builds up the normal generated voltage. Condition to be satisfied are: The rotor of a induction motor never succeeds in catching up with stator field. If it really did, there will be no relative speed between stator and rotor field. Hence, no rotor e. Therefore, no rotor torque to maintain rotation. That is why rotor runs at speed lower than that of stator and stator field runs at N s speed. The necessary phase difference between I s and I m is produced by connecting a capacitor in series with starting winding.

The Capacitor is generally electrolytic type and its usually mounted on the outside of motor. Draw its torque-slip characteristics. The Principle of operation of two-phase servo motor:. For low power few hundred watts control applications, the two phases balanced servo motor is ideally switched. As it can be driven by means of a relatively rugged drift free as an amplifier.

The motor torque can be easily controlled by varying the magnitude of a. The control phase is shifted in phase by 90 0 from the reference phase voltage by means of a phase shifting networks included in voltage application stages of amplifier. For linear stable operation, the speed torque- characteristics of a servomotor must be linear with negative slope torque reducing with increasing speed. It is suitable for the position control system.