JNTUH PEE SECOND MID BITS
UNIT-5: D.C. Generators
1.The type of compound generator commonly used for obtaining an almost constant terminal voltage is[ ] (a) over compound (b)flat compound (c)cumulative compound (d)under compound [ b]
2. In a DC machine, the number of commutator segments is equal to [ c ]
(a)number of conductors (b)number of poles (c)number of coils (d)both a and b
3. The yoke of a dc machine is made up of [ d ]
(a)silicon steel (b)soft iron (c)aluminium (d)cast steel
4. The brushes that carry the current to the load are made up of Carbon
5. Power lost as heat in the armature and field windings of a dc machine is called COPPER loss.
6. A shunt generator delivers 195A at a terminal p.d of 250V. The Ra and Rf are 0.02Ω and 50Ω respectively. The generated emf is254V
7. The field winding of a d.c shunt machine usually carries ______ of the rated current of the machine [ a ]
(a) 2% to 5% (b) 15% to 20% (c) more than 20% (d) less than 0.5%
8. A shunt generator delivers 195 A at a terminal p.d of 250 V. The armature resistance and shunt field resistance are 0.02Ω and 50Ω respectively. What is the value of generated e.m.f? [ c ]
(a) 246 V (b) 270 V (c) 254 V (d) 282 V
9. In a long-shunt compound-wound generator, the shunt field is connected parallel with [ d ]
(a) armature (b) parallel combination of armature and series field
(c) series field (d) series combination of armature and series field
10. In a cumulatively compounded generator, the shunt and series fields aid each other
11. The e.m.f equation of a d.c generator in terms of flux, poles etc is given by Eg = (ΦZNP) / (60 * A)
12. The most economical method of finding no-load losses of a large d.c. machine is Swinburne’s test.
13. The Commutator in a dc machine can be convert [ c]
(a) ac to dc (b) dc to ac (c) both a and b (d) None of the above
14. The emf produced in the dc generator is ____ induced emf [b ]
(a) Statically (b) Dynamically (c) magnetically (d) Electrostatically
15.. DC generator operates on the principle of [ a]
(a) Electromagnetic induction (b) Lenz's law (c) Biov Savart's law (d) none of these
16. Emf equation of generator is Eg = (ΦZNP) / (60 * A)
17. Yoke is made of which material Cast iron or Cast steel
18. Types of windings in dc generator Lap winding ,wave winding
19. The Mechanical energy source used to drive a dc generator is called a [ b ]
(A) Rotor (B) Prime Mover (C) Alternator (D) Motor drive
20. The nature of current having in the armature of a dc machine is _____ [ a ]
a) AC b) DC c) pulsating d) None
21. The induced voltage in a single loop reverses_____ [ a ]
a) Once each revolution b) once each half revolution
c) one each quarter revolution d) 8 times each revolution
22. The field of self excited generator is excited by [ c]
a) Dc b) Ac c) By its own current d) Either ac or Dc
23. The magnetic field which initially induces emf in the armature in a self excited dc generator is Because of Residual magnetism(residual flux)
24. Emf induced in each conductor of a DC Machine is [ a ]
A) An alternating emf B) A direct emf
C) A pulsating emf D) Emf of random waveshape
25. The residual magnetism of a DC shunt generator can be regained by [a ]
A) Connecting the shunt field to a battery B) Running the generator on no load for sometime C) Grounding the shunt field D) Reversing the direction of rotation of the generator.
26. Faraday's second Law states that the magnitude of individual emf is equal to the rate of Change of flux linkages.
27. A four pole DC generator is running at 1500 rpm. The frequency of current in the armature is 50Hz
28. The armature of a dc machine is a laminated to reduce Eddy current losses
29. The function of interpoles in a dc machine is to improve commutation
30. The EMF induced in a coil rotating in a uniform magnetic field is maximum when the flux linkage by the coil is minimum
31. The O.C.C of a d.c. generator is also called its magnetic or no load saturation characteristic.
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