V and inverted v curves of a synchronous motor slideshare ask for details. In fact, a given synchronous machine may be used, at least theoretically, as an alternator, when driven mechanically or as a motor, when driven electrically, just as in the case of d. V and inverted v curves of synchronous motor electrical. Adjust the field excitation of the synchronous machine so that about rated voltage 400v, ll is obtained. The synchronous motor v curves shown above illustrate the effect of excitation field amps on the armature stator amps and on system power factor.
Speed equal to rotating magnetic field produced due to 3phase armature winding. Ammeter reads the line current which is same as armature stator current. Discuss the methods of starting and procedure for starting synchronous motor. Electrical machinesii lab manual pdf emii lab manual pdf. When synchronous motor is working at constant applied voltage, the resultant air gap flux demanded by applied voltage remains constant. In this experiment two watt meter method is used to measure input power of motor. But initial lagging current becomes unity and then becomes. With the given excitation a synchronous motor draws a unity pf current. What is the significance of the v curve in a synchronous. These are known as v curves of synchronous machine by virtue of their shape. In case of synchronous motor revolving field structure is to be energized by direct current. Variation of power factor with field current of motor in exactly reverse fashion, which is called as inverted v curves. In this case, the field circuit of the synchronous machine is closed through high.
If the mechanical load is increased what will be the power factor and current for the same excitation. V and inverted v curves of synchronous motor virtual labs. When the motor attains about 95% of the synchronous speed, the rotor windings is connected to exciter terminals and the rotor is magnetically locked by the rotating magnetic field of stator and it runs as a synchronous motor. The steadystate characteristics of a synchronous motor represented by phasor diagrams are shown as function of the excitation voltage e. Since the shape of these curves is similar to the letter v, thus they are called v curve of synchronous motor. V curves are useful for adjusting the field current. Moreover, there is practically no difference in the construction of the dc generator and the dc motor, and there is no substantial difference in the rating of a machine as a motor or as a generator. If the v curves at different load conditions are plotted and points on different curves having same p. Explain the significance of v and inverted v curves. Pradyumna pooskuru 18 downloads 124 views 229kb size. V and inverted v curves of synchronous motor free download as word doc.
Synchronous motor copyright 2004 kilowatt classroom, llc. Synchronous speed is equal to 120 times the frequency fac, divided by the number of motor poles p. Why v curve shift upwards and inverted v curve shift right as the load. If excitation is varied from very low under excitation to very high over excitation value, then current ia decreases, becomes minimum at unity p. V curve of a synchronous motor v curve is a plot of the stator current versus field current for different constant loads.
This curve is popularly known as vcurve of generator connected to infinite bus. V curves and inverted v curves of synchronous motor. When synchronous motor is working at constant applied voltage, the resultant air. For a constant power, vcurve can only be obtained for generator connected to infinite bus grid. Where f is supply frequency and p is number of poles in motor. V curve and inverted v curve for synchronous generator.
A 3000 v, 3 phase synchronous motor running at 1500 rpm, has its excitation kept constant corresponding to no load terminal voltage of 3000 v. May 15, 2018 synchronous motor excitation refers to the dc supply given to rotor which is used to produce the required magnetic flux. The point of least armature current drawn from stator of synchronous motor will correspond to unity power factor and both graphs will have same field current reading. Draw and explain v and inverted v curves for synchronous. If graph of armature current drawn by synchronous motor is against field current is plotted then the resulted graph is known as a. Jan 08, 2016 these are known as v curves of synchronous machine by virtue of their shape.
Vcurves and inverted vcurves of synchronous motor youtube. What is v curve and inverted v curve of sychronous motor. Vcurves consider a synchronous motor operating at rated mechanical load examine the behavior as the excitation is varied mechanical power remains constant at unity power factor the motor current is at a minimum at unity power factor the total power equals the active power as excitation increases or decreases. Explain how the v and inverted v curves can be obtained in synchronous motor. Jul 12, 20 as against this, if the power factor cos. A synchronous motor is a doubleexcited machine, its armature. A synchronous motor is a doubleexcited machine, its armature winding is energised from an a. Usually starting synchronous machines as an induction motor is quite common.
Synchronous machines have parabolic type characteristics. Synchronous machine structures stator and rotor the armature winding of a conventional synchronous machine is almost invariably on the stator and is usually a three phase winding. Vcurve of generator is a plot of variation of armature current with the change in field current. The vcurve analysis and study of synchronous motors. The graph plotted between the armature current i a and field current i f at no load the curve is obtained known as v curve.
Regulation of 3phase alternator by zpf and asa methods 9. Motor that run at constant speed at all load applied to it. V curve is a plot of the stator current versus field current for different constant loads. By controlling the field current, reactive power supplied to the motor can be controlled. Vcurve of generator is basically a plot of variation of armature current with the change in field current. Inverted v curves the variation of power factor against field current for constant power input. The inverted v curve shows the variation of the armature current by varying the field excitation. Synchronous motors it is known, that the direct current generator operates satisfactorily as a motor.
Electromagnetic devices draw a magnetizing current from the a. The variation of magnitude of line current with respect to the field current is called v curve. This curve is known as v curve because the shape of this curve is similar to the letter v. V curve and inverted v curves are applicable for synchromous machine. Therefore due to damper windings synchronous motor starts as induction motor and continue to accelerate. The two wattmeter method is used to measure input power of motor. Stardelta starting of a three phase induction motor 10. Synchronous machines rotation the axis of the field winding in the direction of the dc field is called the rotor direct axis or the daxis. The input power to a threephase synchronous motor is given by p 3 v i cos. The v and inverted v curve in synchronous machine is a plot of field current on x axis and armature current and pf respectively on the y axis. Since the shape of these curves is similar to the letter v, thus they are called v curve of. One of the major and unique characteristics of this motor is that it can be operated at any electrical power factor leading, lagging or unity and this feature is based on the excitation of the synchronous motor. The graph is plotted between the armature current ia and field current if at no load. Connect stator of motor to 3 phase supply as shown in the above figure through watt meters and ammeter.
Synchronous motor characteristics vcurves the steadystate characteristics of a synchronous motor represented by phasor diagrams are shown as function of the excitation voltage e. Conclusion v curve v curve is the graph showing the relation of armature current as a function of field current in synchronous. Vcurve and power factor control of generator are closely related to each other. The steadystate characteristics of a synchronous motor represented by phasor diagrams are. About this video what is vcurve in synchronous motor what is inverted vcurve in synchronous motor full explanation about under excitation. The ammeter is reading line current which is same as armature stator current. To start induction motor by rotor resistance starter 8. The minimum point of the v curve represent the condition of unity power factor pf. The inverted v curve is a graph showing the relation of power factor as a function of field current. V curves and inverted v curves for synchronous motor. What are v and inverted v curves of synchronous motor.
Sm36 v and inverted v curves of alternator duration. Synchronous machines 2 in this chapter, we concentrate on conventional synchronous machines whereas the brushless dc motors will be discussed later in a separate chapter. The vcurve analysis and study of synchronous motors using. Explain the constructional details of alternator in. The synchronous motor operates at a precise synchronous speed, and hence is a constantspeed motor. By looking at the v curve we can tell that om increasing the excitation of the machine the armature cu. Obviously armature current caused armature reaction which will oppose the field fluxes or the field they are inversely proportional to each other in case of alternator during overexcited state armature current increases and thus it delivers reactive var. Dec 08, 2017 what is inverted v curve in synchronous motor full explanation about under excitation, normal excitation, and over excitation in v curves and inverted v curves relation between field current and. What is the significance of v curve and inverted v curve. When the synchronous motor operates with constant power input, the variation of armature current with field current is thus a shaped curve, as illustrated in.
Explain the constructional details of alternator in detail. The curves are related to the phasor diagram in fig. When synchronous motor is working at constant applied. A little reflection will show that pf versus i f plots will be inverted v curves. To download the complete app of working of a dc series motor. Explain the effect of change of excitation of a synchronous motor on its power factor. This magnetizing current lags the applied voltage by almost 900. Generator vcurve and power factor control electrical concepts. But initial lagging current becomes unity and then becomes leading. After having the concept behind the three cases discussed, it is better to plot a curve between field current and armature current.
V and inverted v curves of a 3phase synchronous motor. Synchronous machines can also be used as motors, but they are usually built in very large sizes. Vcurve and inverted v curve are depicted below figure 1 figure 2 vcurve is plotted between armature current and field current. To repeat the above, with synchronous motor loaded. When its load angle is equal to the impedance angle.
Synchronous and asynchronous synchronousspeedof an ac motor the speed of the rotating magnetic field is referred to as the synchronous speed ns of the motor. To determine positive sequence, negative sequence and zero sequence reactances of an alternator. The graph plotted between the armature current ia and field current if at no load the curve is obtained known as v curve. The purpose of the curve is to show the variation in the magnitude of the armature current as the excitation voltage of the machine is varied inverted v curve. Inverted v curve excitation vs power factor the synchronous motor v curves shown above illustrate the effect of excitation field amps on the armature stator amps and on system power factor. Depicted picture is shown for synchronous motor not for. Hence when the machine operates as a synchronous motor the emf phasor always lags the terminal voltage phasor by the load1torque angle. Commons is a freely licensed media file repository.
At what load angle is power developed in a synchronous motor becomes its maximum value. In stator winding two effects are to be considered the effect of field cutting stator conductors at synchronous speed and the effect of stator revolving field. Inverted v curves a family of curves can be obtained by plotting the power factor versus field current at a constant load of synchronous motor. Mar 25, 2018 v curve and inverted v curve for synchronous generator alternator also v curve of alternator. Information from its description page there is shown below. V curve of synchronous motors waleed 15103122028 2. V terminal voltage r e effective resistance x l leakage reactance x a fictious reactance x s synchronous reactance e counter emf. In synchronous motors performance characteristics obtained by v curves and inverted v curves.
In general, overexcitation will cause the synchronous motor to operate at a leading power factor, while underexcitation will cause the motor to operate at a lagging power. The magnetic field created by the stator currents rotates at the synchronous speed,and that created by the field current on the rotor is. Operating characteristics of synchronous machine eeeguide. A synchronous machine is an ac rotating machine whose speed under steady state condition is proportional to the frequency of the current in its armature. A synchronous does not possess starting torque but once brought near. Stator is connected top three phase supply through wattmeters and ammeter. Though only one figure is drawn for generatingmotoring operation, the actual shape of v curves for the two cases will not be identical. Operational panel for plotting the v curve of a synchronous machine and a dc shunt generator. There are separate v curves for noload and fullload and sometimes the motor manufacturer publishes curves for 25%, 50%, and 75% load. Armature current is obtained by dividing this vector. A short course on synchronous machines and synchronous condensers. Unlike the induction motor, whose operation always involves a lagging power factor, the synchronous motor possesses a variablepowerfactor.
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