For a three phase synchronous motor, answer the following:Why it is not self-starting? List the methods of starting it?Draw its phasor diagram when working on a constant load, over excitation ?Explain how you can reduce hunting in it?Draw its V-curves and inverted V-curves?9Explain how you can use it as a synchronous condenser ?

Answered: For a three phase synchronous motor,…

Electric Motor Control

10th Edition

ISBN:9781133702818

Author:Herman

Publisher:Herman

Chapter39: Synchronous Motor Operation

Section: Chapter Questions

Problem 3SQ: What are typical applications of synchronous motors?

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L-1). How would it be possible to reverse the direction of rotation of a 3-phase synchronous motor? a) reverse the polarity of the DC field excitation b) interchanging any two of the incoming supply lines c) interchanging all three of the supply lines d) none of the above L-2). The amortisseur winding of a 3-phase, synchronous motor is the.....a) squirrel-cage winding on the rotor used to start the motor b) wire wound winding on the rotor to be connected to the external DC supply by way of slip rings and brushes c) either "a" or "b" d) neither "a" nor "b" L-3). Is it ok to have the DC voltage supply connected to the rotor of a 3-phase synchronous motor while starting? a) yes b) no
A three-phase, 60-Hz induction motor runs at 890 r/min at no load and at 840 r/min at full load. (a) How many poles does this motor have? (b) What is the slip at rated load? (c) What is the speed at one-quarter of the rated load? (d) What is the rotor’s electrical frequency at one-quarter of the rated load?
51. When a synchronous motor is said to be ... A) over-excited, it is operating at a a) lagging power factor b) unity power factor c) leading power factor d) none of the above B) under-excited, it is operating at a a) lagging power factor b) unity power factor c) leading power factor d) none of the above C). What is a typical slip of a synchronous motor? a) 0% b) 2-5% c) 7-9% d) none of the above D). Selsyn motors can be used to a) provide position control b) provide angular feedback information c) both "a" and "b" d) neither "a" nor "b"
2.. A three-phase 60 Hz asynchronous motor runs at 890 rpm at idle and 840 rpm at full load. ww w w www wwww a) How many poles does this motor have? b) What will be thę slip at nominal load? c) What happens if the nominal load is slipping at half? www. d) What is the electrical frequency of the rotor at half the nominal load? wwww
A 3 phase, 1500 rpm, 2200 V, star connected synchronous motor has an impedance of 0.4+j90 per phase. At some excitation 2900 V is induced in the armature. Find the maximum torque developed by motor before the motor breaks out of synchronism. Also find the load angle this time.
Sketch the V curve for a synchronous motor. Label the axes. Indicate where the power factor is lagging and where it is leading. Draw the phasor diagram corresponding to the minimum point on the V curve.
A three-phase induction motor is supplied with power from a 60-Hz source. At full load the motor speedis 1728 rpm, and at no load the speed is nearly 1800 rpm. At full-load conditions, determine thefollowing:a) Number of polesb) Slipc) Frequency of the rotor voltages
What are typical applications of synchronous motors?
F-a). Single-phase repulsion motors have......... . a) excellent starting torque b) excellent running torque c) unstable speed characteristics d) all of the above F-b). Which type of repulsion motor runs quieter? a) repulsion b) repulsion-start, induction-run c) repulsion-induction d) they are all the same F-c. Single-phase repulsion-induction motors have........ . a) high starting torque b) good speed regulation c) both "a" and "b" d) neither "a" nor "b"
AA a QUESTION A 750 kW, 3300V, 50 Hz, wound-rotor three-phase induction motor with a star-connected stator winding has a star-connected rotor winding with effective stator/rotor turns ratio of 3.6. The rotor resistance and rotor leakage inductance are 0.0296 2 and 1.7 mH respectively. The stator winding resistance, the stator leakage inductance, and the mutual inductance can be neglected. (a)Calculate the stator current and power factor at a slip of 0.03. (b)Calculate the torque developed at this load. (c) Calculate the stator current and power factor when starting with rated voltage and with the slip-rings short-circuited. (d) What is the main disadvantage of starting big motor using the method described in part (b)? (e)Calculate the resistance of a star- connected external resistor bank that should be connected in the rotor circuit to limit the stator current on starting to 150 (f)By what factor does the addition of the ||| <
Q2] Fill in the blank (9 Marks) 1-The current drwan by the armature of D.C. motor is directly proportional to 2- The speed of a D.C. shunt-wound motor will shunt field regulator is increased. 3- The synchronous speed of a three-phase induction motor is number of pairs of poles. Rotor copper losses Rotor input power in induction motor = 5- A 4-pole three-phase induction motor has a synchronous speed of 25 r.p.s. The frequency of the supply to the stator is_ Hz. 6- The power input to a mains transformer is 200VA. If the primary current is 2.5A, the secondary voltage is 2V and assuming no losses in the transformer, the turns ratio step down. is 7- A 200kVA transformer has an iron loss of 1 kW and full load cu loss of 2 kW. Its load kVA corresponding to maximum efficiency is kVA. 8- If cu loss of a transformer at 7/8th full load is 4900 W, then its full-load cu loss would be watt. 4- if the value of resistance of the proportional to the 9- The slight curvature at the lower end of the open…

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