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 is 254V
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.
UNIT-6: D.C.MOTORS
1. 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
2. Main advantage of differentially compound
motor is that [c ]
(a)stable under heavy loads (b)speed increases to very high
values on no load
(c)speed remains constant if load is not excessive (d)start
under heavy load
3. Which of the following motor should never be
started on no load [ d ]
(a)shunt (b)compound cumulative (c)compound differentially
(d) series
4. The yoke of a dc machine is made up of [ d ]
(a)silicon steel (b)soft iron (c)aluminium (d)cast steel
5. The value of back emf in a dc motor is maximum
at _______ [ a ]
(a)no load (b)full load (c)half full load (d)one fourth
full load
6. The brushes that carry the current
to the load are made up of Carbon
7. Power lost as heat in the armature and field windings of a
dc machine is called copper loss
8. Series dc motor should never be started on
no load.
9. The relation between speed, flux and
back emf in a dc motor is NαEb/Ф
10. 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%
11. The speed of a d.c. motor can be controlled by
changing [ d ]
(a) its flux (b) armature circuit resistance
(c) applied voltage (d) all of the above
12. By putting controller resistance in series with the
armature of a d.c motor, we can obtain speeds
[ b]
(a) above the normal speed only (b) below the normal speed
only
(c) above as well as below the normal speed (d) none of the
above
13. The only
disadvantage of field control method for controlling the speed of a d.c shunt
motor is that it [ c]
(a) give speeds lower than the normal speed (b) is wasteful
(c) needs a large rheostat (d) adversely affects
commutation
14. The motor terminal voltage equation
is given by V = Eb+ IaRa
15. The most economical method of
finding no-load losses of a large d.c. machine is swinburne’s test.
16. 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
17. Fleming's left hand rule is applicable for: [b ]
(a) dc
generator (b) dc motor (c) alternator (d) Transformer
19.. The armature torque of the dc shunt motor is
proportional to [a ]
(a) armature current only (b) field flux only (c) armature
current and flux both (d) None
20.. Motor which should not run at no-load is [a ]
(a) Series motor (b) shunt motor (c) compound motor (d) induction
motor
21. Yoke is made of which material Cast iron or Cast steel
22 Losses in DC machine are Iron losses,Cu
losses, Mechanical losses
23. Types of DC motors , D.C series motor,
d.c shunt motor
24. In DC shunt motor the Torque is directly proportional
to Ia
25. High permeability magnetic materials helps [a ]
A) To confine the flux within the magnetic circuit. B) To
allow the flux to leak
C) In producing more current. D) None of the
26. A Commutator in a DC machine can convert ____
to ______ [ c]
(a) AC, DC (b) DC, AC (c) either ‘A’ or ‘B’ (d) None
27. The current flowing through armature
conductors of a dc motor is _____________ [c ]
a) Pulsating b) Dc c) Ac d) none of these
28.. In Swinburne’s test of a Dc machine [ b]
a) No load losses are calculated and
copper losses are measured
b) No load losses are measured and
copper losses are calculated
c) Both the losses are measured
d) Both the
losses are calculated
29. The supply terminals for a dc shunt motor are
reversed. What will be effect on the motor [b ]
a) It will run as Dc generator b) runs in reverse direction
c)it stops d)its burns
30. The starting resistance for a dc
shunt motor Low
31. A 3 point starter is considered
suitable for dc Shunt motor
32. The magnitude of force acting on a current
carrying conductor placed in a magnetic field is
independent of [ c ]
A) Flux density B) length of conductor
C) cross-sectional area of conductor D) current flowing
Through the conductor
35. When a dc machine is connected in the dc
supply main it will produce [ d]
A) Emf in opposition to applied voltage. B) Unidirectional
torque
C) Copper losses in the windings D) all of the above
36. 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
37. The starting torque of a dc shunt motor is [b ]
A) Zero B) low C) high D) very high.
38. The armature of a dc machine is a
laminated to reduce Eddy current losses
39. If the flux of a dc motor approaches
zero its speed will Infinite
40. The direction of mechanical force
experienced on a current carrying conductor placed in a magnetic Field is
determined by Fleming’s left hand rule
41. The function of interpoles in a dc
machine is to improve commutation
42 The speed of a DC motor is directly
proportional to its Back emf and
inversely proportional
To Flux
43. The current drawn by a dc motor at
the starting instant will be High
44. The eddy current losses is directly
proportional to [ b ]
a) f b)f^2 c)f^1.6 d)f^3
45. The iron losses [ d]
a) core losses b) eddycurrent losses c) hystersis losses d)
all the above
46.. The speed of a d.c motor can be controlled by
varying [d ]
a)its flux per pole b)resistance of armature circuit c)applied
voltage d)all the above
47.. The collection of current from
armature conductors to the external load is the function of Commutator and brushes
48. The iron or core losses are also
known as Constant losses
49. In d.c motor unidirectional torque
is produced with the help of-Brushes-and
commutator.
50 Under constant load conditions, the
speed of a d.c motor is affected by V, Ra, Ø
51. The Eb/V ratio of a d.c motor known
as Efficiency
52. An invertor is employed to convert DC voltage to AC voltage
UNIT-7:
TRANSFORMERS and Their Performance
1.
If rated Dc voltage is applied
instead of AC to the primary of a transformer then primary winding of the transformer will burn.
2. If Pi be the iron losses and Pc be
the copper losses on full load, then the condition for obtaining the maximum
efficiency at 3/4th full load is
Pc= (16/9) Pi
3. A transformer can have Zero regulation at leading power
factor.
4. the chemical used in breather is silica gel
5. The no load current in a transformer lags the applied
voltage by 75˚
6. Condition for maximum efficiency of
Transformer is Constant losses =variable losses
7. In a
Transformer Core is laminated to reduce Eddy
current loss
8. A transformer has
an efficiency of 80% and works at 100V, 4KW. If the secondary voltage is 240V,
find primary current [a ]
(a)40A (b)30A (c)20A (d)10A
9. The no load current of a
transformer is generally of the order of _______the full load current [a ]
(a)less than 5% (b)more
than 5% (c)equal to that (d)zero
10. The core losses in
a transformer consists of Hysteresis and Eddy current losses
11. The voltage
regulation of a transformer can be determined by conducting OC and SC
tests.
12. A transformer transfers electrical energy from
primary to secondary usually with a change in [ a]
(a) frequency (b) power
(c) voltage (d) time period
13. The open-circuit test on a transformer is
always made on [ a]
(a) low-voltage winding (b) high-voltage
winding
(c) either low or high
voltage winding (d) none of the above
14. The open-circuit
test on a transformer gives Iron losses
15. A transformer has full-load copper loss of 400 W.
The copper loss at half-full load will be 100W
16. Transformer
operates on AC only.
17. A transformer
steps up the voltage by a factor 100. The ratio of current in the primary to
that in secondary is 100
18. If Pi be the iron losses and Pc be the full load losses, the
load current at which maximum efficiency occurs is ____________ times of full
load current
19. Efficiency of a transformer is maximum if Iron losses=cu losses
20. The Iron core in a
transformer provides a Low reluctance path to the main flux.
21. The Principle of operation of a Transformer is
[ B]
(A) Electromagnetic Induction
(B)Mutual Induction
(C) Varying a conductor in
a magnetic field (D) Electrostatic induction
22. The flux involved in the emf equation of a
transformer has [ D]
(A) RMS value (B) Average
value (C) Total value (D) Max. value
23. In a single phase transformer, with subscripts
1 and 2 for primary and secondary windings[a ]
(A) E1N2= E2N1 and I1N1= I2N2 (B) E1N1= E2N2 and I1N1= I2N2
(C) E1N2= E2N1 and I1N2= I2N1 (D) E1N1= E2N2 and I1N2= I2N1s
24. The Regulation of
a Transformer is zero, when the Power factor is leading
25. Eddy current losses in a transformer core can
be reduced by _____ [ a ]
(a) Reducing the thickness (b) decreasing
air gap in the magnetic circuit
(c) Increasing air gap in
the magnetic circuit. (d) Increasing the thickness
UNIT-VIII: Single phase
induction motors
1. At starting, the line current of a capacitor start
induction motor is ______ the normal full load current[ b ]
(a)8 to 10 times (b)4 to 5
times (c) equal to (d)7 to 8 times
2. The main winding and starting winding of a
single phase induction motor are connected in__________ across the supply. [b ]
(a)series (b) parallel
(c)series parallel (d)none
3. In
capacitor start induction motor the angle between Im and Is is about 75˚
4. The
purpose of starting winding in a single phase induction motor is to produce rotating flux
5. A
single phase induction motor employs squirrel cage
rotor
6. The main winding and starting winding of a
single-phase induction motor are connected in ________ across the supply [b ]
(a) series (b) parallel (c)
series-parallel (d) none of the above
7. A two-phase a.c. servometer has [b ]
(a) wound rotor (b) cage
rotor (c) wound or cage rotor (d) a rotor similar to that in d.c motors
8. A
50 Hz, 4-pole, single-phase induction motor will have a synchronous speed of 1500 RPM
9. The
full-load efficiency of a shaded-pole motor is about 30 to 35 %.
10. The
amount of torque required to move a stepper motor one full step is called holding torque
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