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Dc machine
1-Dont try to cram or spend more time here just read it fast and cover syllabus then practice MCQ's cheptor of same topic to check your progress. . |
2-Wrong options are also given but dont concentrate there, Right answer is in bold format. |
Q21 ⇒ A 3 point starter is considered suitable for dc ____ motors shunt [other wrong options] [Discuss in forum] series compound shunt as well as compound series as well as compound |
Q22 ⇒ In regenerave braking, the motor energy is |
Q23 ⇒ The most economical method of electric braking is regenerative braking. [other wrong options] [Discuss in forum] plugging. dynamic braking with separate excitation. dynamic braking with self excitation. |
Q24 ⇒ In a dc machine, mechanical losses are primarily function of speed. [other wrong options] [Discuss in forum] voltage. current. none of these. |
Q25 ⇒ Dynamic braking is very effective if the dc motor is separately excited. [other wrong options] [Discuss in forum] is series excited. is shunt excited. has cumulative compound excitation. I.\.J. |
Q26 ⇒ Core loss in a dc machine occurs in armature only [other wrong options] [Discuss in forum] pole shoe only yoke only in all the above three. |
Q27 ⇒ The variable loss in a dc shunt machine is armature copper loss. [other wrong options] [Discuss in forum] iron loss. shunt field loss. friction and windage loss. |
Q28 ⇒ The maximum efficiency occurs in a separately excited dc generator
when the terminal voltage is 220 V and the induced emf is 240 V,
the stray losses, if the armature resistance is 0.2 Ω, will be: 2,000 W [other wrong options] [Discuss in forum] 1,000 W 3,000 W 4,000 W |
Q29 ⇒ In a dc shunt machine, hysteresis loss all of the above. [other wrong options] [Discuss in forum] is independent of lamination thickness. varies as the supply frequency. varies as 1.6 power flux density. varies as the volume of the iron core. |
Q30 ⇒ In direct method of determination of efficiency of a dc machine the machine is actually loaded and input power and output power are measured [other wrong options] [Discuss in forum] copper losses, magnetic losses and mechanical losses are
measured. either (a) or (b). none of these. |
Q31 ⇒ In a dc machine, armature copper loss varies as (load current)2 [other wrong options] [Discuss in forum] load current. 1/load current. 1/(load current)2 |
Q32 ⇒ Performance of large dc machines regarding commutation and
temperature rise etc. at full load can be checked by ____ test. Hopkinson's [other wrong options] [Discuss in forum] brake Swinburne's running down |
Q33 ⇒ Which of the following motors is expected to have maximum fullload
efficiency? 100kW [other wrong options] [Discuss in forum] 1kW 5kW 30kW |
Q34 ⇒ In Hopkinson's efficiency test for dc machines |
Q35 ⇒ Indirect method of testing is preferred because all of the above. [other wrong options] [Discuss in forum] it enables the determination of losses without actually loading
the machine power requirement is very small and so large machines can be tested economically and conveniently it does not require any loading arrangement. the efficiency can be determined at any load. |
Q36 ⇒ In Hopkinson's and field's tests, the main common thing is that both tests use two identical mechanically coupled dc machines [other wrong options] [Discuss in forum] both tests are regenerative. the power drawn in both the tests is negligible to meet the internal losses only. all of the above |
Q37 ⇒ In case of a cross-field machine, the amplification ratio maybe as
high as 10,000:1 [other wrong options] [Discuss in forum] 2,000:1 500:1 100:1 |
Q38 ⇒ Which of the following statement(s) associated with a Rosenberg
generator is/are incorrect? It is a constant voltage generator at low speeds. [other wrong options] [Discuss in forum] It is an armature excited high speed machine. It provides constant cunent over wider limits of speed. It is essentially a 2-pole machine with two sets of brushes arranged on the axis at right angles to each other Its voltage polarity is independent of direction of rotation. |
Q39 ⇒ The inductor of a three-wire generator should he iron-cored so as
to reduce the current through it. [other wrong options] [Discuss in forum] increase the current through it. reduce the voltage ripples in the output circuit improve the voltage regulation of the machine. |
Q40 ⇒ For preventive maintenance of ade machine it is to be ensured that all of the above [other wrong options] [Discuss in forum] insulation resistances of the field and armature windings are
proper commutator and brushes are in good condition. bearings are properly greased motor and its control gear are free from oil and grease. |
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