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. Electrical machines expected mcq pdf 8 for coal india limited cil mt exam 2017. Since the shape of these curves is similar to the letter v, thus they are called v curve of. Hence when the machine operates as a synchronous motor the emf phasor always lags the terminal voltage phasor by the load1torque angle. What is the difference between iv curve and jv curve. What are v and inverted v curves of synchronous motor. Ammeter reads the line current which is same as armature stator current. In case the field current is made more than its normal excitation, i.
True synchronous motors are driven by sine waveforms. You may do so in any reasonable manner, but not in. When w and wm are converted into cycles per second or hz and revolutions per minute respectively, we have. What is the significance of v curve and inverted v curve. This magnetizing current lags the applied voltage by almost 900. The steadystate characteristics of a synchronous motor represented by phasor diagrams are shown as function of the excitation voltage e. Synchronous condensor synchronous condensor is also known as synchronous compensator or synchronous phase modifier. However, the rotor can be shifted in phase by angle.
V and inverted v curves of three phase synchronous motor aim. V curve and inverted v curve are depicted below figure 1 figure 2 v curve is plotted between armature current and field current. When the assembled motor is in operation, the stator windings are connected directly to the power source. The arms of the v are under and overexcited regimes which generate reactive power output. Typically, the synchronous machine vcurves are provided by the manufacturer so that the user can determine the resulting operation under a given set of conditions.
Effect of field current changes on synchronous motor. The block diagram shows the drive electronics associated with a low voltage 12 v dc synchronous motor. The curves are related to the phasor diagram in fig. Unit ii synchronous motor ee8401 syllabus electrical machines 2 principle of operation torque equation operation on infinite bus bars v and inverted v curves power input and power developed equations starting methods current loci for constant power input, constant excitation and constant power developedhunting. Electromagnetic devices draw a magnetizing current from the a. Exp1 performance of a threephase synchronous motor.
Two or threephase drive may be used by supplying the appropriate number of windings in the stator. Unlike the induction motor, whose operation always involves a lagging power factor, the synchronous motor possesses a variablepowerfactor. Information from its description page there is shown below. Commons is a freely licensed media file repository. A family of vcurves may be obtained for a given motor by observing the above relations for a number of values of constant power inputs. For a constant load, if the power factor is plotted against various values of field exciting current, the curve formed is inverted v shape and called as inverted v curve. Synchronous motors controlled by variablespeed drives are. In this experiment two watt meter method is used to measure input power of motor. When synchronous motor is is said to receive 100% excitation. 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. Typically, the synchronous machine v curves are provided by the manufacturer so that the user can determine the resulting operation under a given set of conditions. May 15, 2018 synchronous motor excitation refers to the dc supply given to rotor which is used to produce the required magnetic flux.
A short course on synchronous machines and synchronous condensers. Measurement of x1, x2 and xo of a synchronous generator and calculation of currents. 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. Download link is provided and students can download the anna university ee6504 electrical machinesii em ii syllabus question bank lecture notes syllabus part a 2 marks with answers part b 16 marks question bank with answer, all the materials are listed below for the students to make use of it and score good maximum marks with our study materials. When the synchronous machine is connected to infinite bus v, the rotor must turn at angular frequency.
It can generate or absorb reactive voltampere var by varying the excitation of its field winding. About this video what is vcurve in synchronous motor what is inverted vcurve in synchronous motor full explanation about under excitation. Vcurve of a synchronous machine shows its performance in terms of variation of armature current with field current when the load and input voltage to. The vcurve analysis and study of synchronous motors using.
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. Pradyumna pooskuru 18 downloads 124 views 229kb size. There are separate v curves for noload and fullload and sometimes the motor manufacturer publishes curves for 25%, 50%, and 75% load. Synchronous motor characteristics v curves the steadystate characteristics of a synchronous motor represented by phasor diagrams are shown as function of the excitation voltage e. A synchronous motor starts as usual but fails to develop its full torque. Construction of vcurves the v curves of a synchornous motor show how armature current varies with its field current when motor inpu t is kept constant. Pdf ee6504 electrical machinesii emii books, lecture.
V curve and inverted v curves are applicable for synchromous machine. Load test on single phase squirrel cage induction motor aim. For drawing v curves and inverted v curves of synchronous motor following measuring instruments and accessories. At what load angle is power developed in a synchronous motor becomes its maximum value. V curve and inverted v curve for synchronous generator. Title of the paper 18pt times new roman, bold semantic scholar. Synchronous machines can also be used as motors, but they are usually built in very large sizes. Synchronous and asynchronous electromechanicalsystems dr. The synchronous motor operates at a precise synchronous speed, and hence is a constantspeed motor. 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.
A synchronous motor is a doubleexcited machine, its armature. Dec 08, 2017 about this video what is v curve in synchronous motor what is inverted v curve in synchronous motor full explanation about under excitation, normal excitation, and over excitation in v curves and. Bh curve experiment manual pdf laboratory manual v and inverted v curves of a 3phase synchronous motor. V and inverted v curves of synchronous motor effect of change in excitation of synchronous motor. The vcurve is used to describe the power output of a synchronous machine with regard to the excitation current.
The two wattmeter method is used to measure input power of motor. V curves and inverted vcurves of synchronous motor a synchronous motor is a doubleexcited machine, its armature winding is energized from an a. Vcurve of a synchronous shows its performance in terms of variation of machine armature current with field current when the load and input voltage to the is constant. 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. V and inverted v curves of synchronous motor effect of. Jun 04, 2015 construction of v curves the v curves of a synchornous motor show how armature current varies with its field current when motor inpu t is kept constant. Since the shape of these curves is similar to the letter v, thus they are called v curve of synchronous motor. The ammeter is reading line current which is same as armature stator current. The synchronous reluctance motor magnetic reluctance is the magnetic equivalent of the resistance in electrical. The vcurves and inverted vcurves of the 3phase synchronous motor have been drawn. V curve and inverted v curve for synchronous generator alternator also v curve of. The synchronous motor v curves shown above illustrate the effect of excitation field amps on the armature stator amps and on system power factor.
A vcurve of a synchronous motor shows the relation between armature currents as ordinates and field currents as abscissas when the motor operates with a constant power input at rated terminal voltage. V curve of a synchronous motor v curve is a plot of the stator current versus field current for different constant loads. V curve and inverted v curve for synchronous generator alternator also v curve of alternator. Synchronous machines the inductance of the stator winding depends on the rotor position energy is stored in the inductance as the rotor moves, there is a change in the energy stored either energy is extracted from the magnetic field and becomes mechanical energy that is, its is a motor or energy is stored in the magnetic field and. Mar 25, 2018 v curve and inverted v curve for synchronous generator alternator also v curve of alternator. V and inverted v curves of synchronous motor electrical. I have a curve that has taken from keithley 2450 sourcemeter. A short course on synchronous machines and synchronous. The vcurve analysis and study of synchronous motors. Synchronous motor copyright 2004 kilowatt classroom, llc. 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. Oct 29, 2016 bh curve experiment manual pdf laboratory manual v and inverted v curves of a 3phase synchronous motor. About this video what is vcurve in synchronous motor what is inverted vcurve in synchronous motor full explanation about under excitation, normal excitation, and over excitation in vcurves and. Regulation of 3phase alternator by zpf and asa methods 9.
Stardelta starting of a three phase induction motor 10. If graph of armature current drawn by synchronous motor is against field current is plotted then the resulted graph is known as a. Stator is connected top three phase supply through wattmeters and ammeter. There are separate v curves for no load and full load and some. Synchronous and asynchronous electricmotors the electric motor is an electromechanical continuous energy conversion equipment that converts electrical energy into electrical energy mechanical energy. The curve displayed the properties of a pn junction. Vcurves and inverted vcurves of synchronous motor youtube. The corre sponding induction motor im however, has slip losses and rotates only at 1475rpm for a chosen 30 kw example. Ee8401 syllabus electrical machines 2 regulation 2017 anna. This file is licensed under the creative commons attributionshare alike 3.
To start induction motor by rotor resistance starter 8. One well known approach is the utilization of synchronous motors sm. The synchronous motor either run at synchronous speed or it will not run at all. Why doesnt the v curve of a synchronous motor touch the. 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. Fig1 shows the variation of armature current and power factor with field current at no load, half load and full load conditions. A synrm rotor has neither a conducting short circuit cage as with the im, nor permanent magnets, nor a field excitation winding. Armature current is obtained by dividing this vector. A synchronous condenser or a synchronous compensator is a synchronous motor running without a mechanical load. A plot of bh where both b and h vary between a positive. Electrical machines expected mcq pdf 8 for coal india. When its load angle is equal to the impedance angle. Synchronous speed is directly proportinal to frequency,similar ti induction motors constant flux operation below base speed is achiecved by operating the synchronous motor with constant v f ratio. 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.
The bottom tip of the v is pure active power output from the machine. V curve and inverted v curve for synchronous generator alternator. V curve of a synchronous shows its performance in terms of variation of machine armature current with field current when the load and input voltage to the is constant. Synchronous motor excitation refers to the dc supply given to rotor which is used to produce the required magnetic flux.
To draw the v and inverted v curves of three phase synchronous motor. Sms with a 4pole rotor operated at 50hz rotate in synchronism with the supply at exactly 1500rpm. V curves and inverted v curves of synchronous motor. For simplicity, the stator winding resistance rs has been neglected. To conduct the load test on single phase squirrel cage induction motor and to draw the. Synchronous machines 6 where w is the angular frequency of emf in electrical radians per second and wm the angular speed of the rotor in mechanical radians per second.
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