To determine voltage regulation of threephase alternator by synchronous impedance method. Hence, the value or regulation so obtained is always more, than that found from an actual test. The regulation of a synchronous generator alternator is. In this method both the reactance drops are replaced by their equivalent mmfs. Thetwocomponents,resistanceand inductance,form a resultantimpedancewhichmay be designated asthe workingimpedanceof the armature. Pdf principles of electrical machines book by vk mehta. Do you need an answer to a question different from the above. A convenient way to compare the voltage behaviour of two generators is by their voltage regulation vr. To study and measure positive, negative and zero sequence. To full fill new increased load, two alternators connected in parallel with bus bar. It is used because the motor is calibrated in the sense that all it losses have been determined for varying condition of operations so that its output is then readily be obtained. Voltage regulation of alternator by emf method and solved. Electrical machines 2 important questions ee8401 pdf free.
Explain any one method of predetermining the regulation of an alternator. The synchronous impedance method is based on the concept of replacing the effect of armature reaction by an imaginary reactance the magnetomotive force mmf. Efficiency of an alternator is calculated by measurement of losses method. The methods employed for determination of regulation are emf or synchronous impedance method, mmf or ampere turns method and the zpf or potier triangle method. Succinctly divided in 14 chapters, the book delves into important concepts of the subject which include armature reaction and commutation. Methods to determine voltage regulation of alternator. The voltage regulation depends upon the power factor of the load. With what condition synchronous motor can be used as a synchronous condenser. Full text of the measurement of synchronous impedance.
Name the various methods for predetermining the voltage regulation of 3phase alternator. Voltage regulation of threephase alternator free download as pdf file. When a balanced load is connected across stator winding a balanced set of 3 phase currents flow with a phase relation with no load voltage depen. To study and measure direct and quadrature axis reactance of a 3 phase alternator by slip test 4.
In this experiment, the emf and mmf methods are used. Normally for voltage regulation calculation, we use methods like. Ee8401 important questions electrical machines 2 regulation 2017 anna university free download. The regulation of a 3phase alternator may be predetermined by conducting the open circuit oc and the sort circuit sc tests. Voltage regulation of transformer plz use speakers. The open circuit voltage and short circuit current of a 3 phase, star connected alternator are 1050 v and 250 a respectively.
In principle, any ac electrical generator can be called. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. The book principles of electrical machines book by vk mehta and rohit mehta is an ideal text for students who look to gain a current and clear understanding of the subject as all theories and concepts are explained with lucidity and clarity.
In the before methods that is voltage regulation of synchronous machine by e. Synchronous impedance method or emf method ii ampere turns method or mmf method iii zero power factor method or potier triangle method iv. The open circuit voltage e 0 of the alternator is given by, phosor sum the diagram has been drawn with the current as the reference phasor and is self explanatory. Sri venkateswara college of engineering and technology. Which of the method more accurate for determine the. Squirrel cage bars placed in the rotor pole faces of an alternator help reduce hunting a above synchronous speed only b below synchronous speed only c above and blow synchronous speeds both d none of the above ans. Discuss briefly the load charactertics of alternator for different power factor. Alternators electrical engineering questions and answers.
The synchronous impedance zs, found is always more than its value under normal voltage conditions and saturation. Or the numerical value of the regulation is defined as the percentage rise in voltage when full load at the specified powerfactor is switched off with speed. Blondels two reaction theory, phasor diagram, direct axis and quadrature axis synchronous reactances, power angle characteristics, slip. There are various methods for determination of regulation one of them is synchronous impedance method is based on the concept of. To calculate voltage regulation of synchronous machine by m. The open circuit characteristic is the graph of the circuit. Voltage regulation of threephase alternator electrical. Explain the effect of change of excitation of a synchronous motor on its armature current. The voltage regulation of a threephase alternator can also be determined using the synchronous impedance method. Figure shows the complete phasor diagram for the mmf method. Electrical machines short answers instrumentation tools. Compared to other methods, the value of voltage regulation obtained by the synchronous impedance method is always higher than the actual value and therefore this method is called the pessimistic method.
Synchronous impedance method the synchronous impedance method or emf method is based on the concept of replacing the effect of armature reaction by an imaginary reactance. The range of abnormal conditions and faults that can occur is extensive, and many could result in serious damage to the alternator and associated plant. Explain synchronous impedance method for determining regulation of an alternator. Explain why the potier reactance is slightly higher than leakages reactance. The synchronous impedance method of finding the voltage regulation by a cylindrical rotor alternator is generally considered as the test data obtained at the rated speed on a threephase yconnected synchronous generator are given as follows. The regulation of a synchronous generator alternator is the rise in voltage at the terminals when the load is reduced from full load rated value to zero, speed and field current remaining constant. Objective questions on alternator page 2 electrical. The following are the three methods which are used to predetermine the voltage regulation of smooth cylindrical type alternators. The alternator terminals are short circuited by closing tpst switch through an ammeter. Protection of synchronous generators involves the consideration of faults and harmful abnormal operating conditions, more so than the protection of other power system elements. An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current.
The usual method of measuring synchronous impedance is by the short circuit test, which consists in running the alter nator at normal speed with its armature short circuited thru an ammeter. Then the synchronous impedance of alternator will be a. Ee8401 question paper electrical machines 2 regulation 2017. Synchronous alternator protection principles and systems. Voltage regulation of an alternator is defined as the change in terminal voltage from no load to full load expressed as a percentage of rated voltage when the load at a given power factor is removed with out change in speed and excitation. Synchronous impedance of a wyeconnected alternator. Ppt alternator powerpoint presentation free to view.
Synchronous impedance method of finding voltage regulation of an alternator is called pessimistic method because a. Synchronous impedance method armature turn or mmf method zero pf or potier method synchronous impedance method gives result which is higher than the original value. Thereactanceofarmaturereactionand regulationbytheoptimisticmethod 34. Chapter 4 synchronous generators or alternators notes. For calculating the regulation, the synchronous method requires the following data. Zero power factor zpf methodpotier triangle method of. Apr 29, 2020 chapter 4 synchronous generators or alternators notes, electrical machines, electrical engineeri ssc je notes edurev is made by best teachers of ssc je. Contents defination methods to determine voltage regulation 1 synchronous impedance method 2 mmf method 3 zero power factor method 3. A no load voltage is induced in the stator coils of alternator when rotor is rotated by a prime mover. Figure 1224 shows the circuit used to determine the synchronous impedance of a wyeconnected ac generator. Voltage regulation of alternator emf and mmf methods.
Synchronous impedance then, synchronous reactance, fig 5 shows the phasor diagram of the alternator, supplying full load current of i a ampere, lagging the terminal voltage v by an angle. Voltage regulation of alternator and solved example youtube. Online multiple choice questions ee synchronous generator. Adams engineering college, paloncha eee department emii lab experiment no. What are the special applications of an over excited synchronous motor. In this process, new running alternator is connected to bus bar by matching frequency v by synchroscope.
Mmf method of voltage regulation its phasor diagram. Explain the effect of change of excitation of a synchronous motor on its power factor. A quite accurate and simple method of determining the losses is to use a calibrated d. And determine the full load regulation of a three phase synchronous generator by synchronous impedance method 3. In this method also it is assumed that the magnetic circuit is unsaturated. Mmf method of voltage regulation mmf method is also known as ampere turn method. Alternator if there are n ph turns per phase, then synchronous generator e ph 4. Why is the synchronous impedance method of estimating voltage regulation considered as pessimistic method. To pre determine the regulation of an alternator at full load at different power factors using synchronous impedance and mmf methods. Short questions and answers ee1251 electrical machines ii. Synchronous machines notes part2 electric equipment. For high capacity alternators, which method is not suitable for finding percentage regulation.
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