Basic_Electrical_Engineering_4th_edition
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394 |
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ELECTRICAL ENGINEERING |
126. |
The rotorofa 1-phase inductionmotoris |
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(a) acage or wound rotor |
(b) always a cage rotor |
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(c) always a wound rotor |
(d) a double cage rotor. |
127. |
In a capacitor start motor, the capacitor is connected |
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(a) in series withthe main winding |
(b) in series with the auxiliary winding |
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(c) in parallel with the auxiliary winding |
(d) in series with both the windings. |
128. A ceilingfan uses |
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(a) split phase motor |
(b) capacitorstartcapacitorrun motor |
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(c) capacitor start motor |
(d)universalmotor. |
129. |
Atwo-phase servo-motor has |
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(a) woundrotor |
(b) cage rotor |
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(c) wound or cage rotor |
(d) double cagerotor. |
130. |
The motor used in electric toys is |
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(a) split phase motor |
(b) permanent capacitor motor |
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(c) shaded pole motor |
(d) capacitor start motor. |
131. |
The voltage fed tothetwowindings ofa two-phase servo motor must be |
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(a) in phase with each other |
(b) goo apart with each other |
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(c) 180° apart with each other |
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(d) more than goo but less than 180° apart with each other. |
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132. |
A stepper motor is a |
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(a) de motor |
(b) single phase ac motor |
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(c) two-phase motor |
(d) multi-phase motor. |
133. |
Phantom loading heat run test on transformers is performedby means of |
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(a) S.C. Test |
(b) O.C. Test |
(c)Halftime on S.C. and halftime on D.C. test
(d)Sumpner's Test.
134.A power transformer has its maximum efficiency at 43 th full load. Its iron loss and full load copperloss Pc are related as
(a)P/Pc = g16
(c)P/Pc = 34
135.In case ofa transformer the low voltage winding is placed near the core because
(a) itreduces insulationrequirement |
(b) it reduces hysteresis loss |
(c) it is convenient |
(d) it reduces eddycurrent loss. |
MULTIPLECHOICE QUESTIONS |
397 |
154. In Swinburne's test for de machine for determination ofefficiency ofthe machine
(a) both the no load losses and the copperlosses are measured (b) boththe no load losses and the copper losses are calculated
(c) The no load losses arecalculated and copper losses are measured (cl) the no load losses are measured andcopperlosses are calculated.
155.Ad.c. shunt motor is drivinga mechanical loadatratedvoltage andrated excitation. Ifthe load torque is doubled, the speed ofthe motor
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(a)increases slightly |
(b) decreases slightly |
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(c) becomes half |
(cl) becomesdouble. |
156. |
The core losses in a d.c. machine occur in |
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(a) the armature only |
(b) the yoke only |
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(c) both the armature and pole faces |
(d) the pole faces only. |
157. |
During noloadtest an inductions motor draws power |
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(a)forcore andcopper loss |
(b) forcore andwindage and frictionloss |
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(c)forcopperloss andwindage andfrictionloss |
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(cl) none ofthe above is true.
158.In case ofa double cage rotor
(a)the outer cage has high resistance and the inner cage low
(b)the outer cage has low resistance and the inner cage high
(c)both the cages have high resistances
(cl) both the cages have lowresistances.
159. Thevariable load on a 3-phase induction is electricallyrepresented by
(a) a variable capacitance (b) a variableinductance (c) a variable resistance
(cl) a combination ofvariable resistance andinductance. 160. Cogging ofinduction motor occurs due to
(a)vibratingtorque
(c) harmonic induction torque only
(cl) both harmonic induction and synchronous torques.
161.Thepower input toan induction motor at 5% slip is 40kW. Assumingthe stator resistance and core loss to be negligibly small, the torque developed by the motor is
(a) 40 kW |
(b) 42 kW |
(c) 38 kW |
(d) 28 kW. |
162.The starting current ofan induction motor is five times the full load current and the full load slip is 4%. The ratio of starting torque to full load torque is
(a) 1.6 |
(b) 1.0 |
(c) 0.8 |
(d) 0.866. |
163.By addinga resistance intherotorcircuit ofa slip ringinduction, the starting current and torquerespectively
398 |
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ELECTRICAL ENGINEERING |
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(a) increase andincrease |
(b) decreaseandincrease |
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(c) decrease and decrease |
(d) increase and decrease. |
164. |
Star-delta startingis equivalentto autotransformerstartingwithtapping as |
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(a) 33% |
(b) 86.6% |
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(c) 58% |
(d) 70.7%. |
165. |
Speed control bysupplyvoltage variation is notresortedto as |
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(a)therange ofspeedcontrol is limited |
(b) It reduces pull out torque |
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(c) (a) and (b) |
(d) none ofthe above. |
166.Inthe capacitor motorifc1 is the capacitance requiredfor best startingtorque andc2 is the
capacitance required forbest running condition, then
(a) c1 is approximately equal to c2 (b) c1 is much smaller than c2
(c) c1 is much lager than c2 |
(d) none ofthe above is necessary. |
167.A synchronous motor is operating at constant load and its excitation is adjusted to give
unity p.f. Ifthe excitation is further increased, the p.f. will be (a) unity only (b) lead
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(c) lag |
(d) zero. |
168. |
A synchronous motor is floating on infinite bus at no load. It's excitation is increased |
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(a) it will not draw any current |
(b) it will draw zero p.f. lagging current |
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(c) it will draw unity p.f. current |
(d) it will draw zero p.f. leading current. |
169. |
The salient pole rotors are not used forhigh speed turbo alternatorbecause of |
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(a)highcentrifugal force andwindage loss |
(b) high eddycurrent loss |
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(c) excessivebearingfriction |
(d) all ofthe above. |
170.The diameter and length ofthe stator bore of a turbo-alternator as compared to a hydro alternator forthe same ratings are respectively
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(a) smaller and larger |
(b) smaller and smaller |
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(c) larger and smaller |
(d) larger and larger. |
171. |
In calculating voltage regulation for an alternator tickoutthe correct answer |
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emf. method |
mmf. method |
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(a) optimistic |
pessimistic |
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(b) optimistic |
optimistic |
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(c) pessimistic |
optimistic |
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(d) pessimistic |
pessimistic. |
172. |
Short circuit ratio (SCR) ofa synchronous machineis defined as the ratio of |
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(a) field current required to produce ratedvoltage on full load andfield current requiredto produce rated current on S.C.
(b) field current required to produce rated voltage on O.C. and field current required to produce rated armature current on S.C.
(c) field current requiredto produce ratedvoltage on full load andfield current required to produce ratedvoltage on S.C.
MULTIPLECHOICE QUESTIONS |
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(d) field current required to produce rated voltage on S.C. and field current required to produce rated current on S.C.
173.An alternatoris deliveringcertainpowerat laggingp.f. andis connected to aninfinitebus. Ifits excitation is increased, itsp.f. and power angle respectively.
(a) increase andincrease |
(b) increase and decrease |
(c) decrease andincrease |
(d) decrease anddecrease. |
174.In Q. 173, ifexcitation is increased, other conditions remaining same, the reactive power andcurrentrespectively
(a) increase andincrease |
(b) increase and decrease |
(c) decrease andincrease |
(d) decrease anddecrease. |
175.In Q. 173, ifthe alternator is deliveringpoweratleadp.f. andifthe excitationis increased, its p.f. and power angle respectively
(a) increase and increase |
(b) increase and decrease |
(c) decrease and increase |
(d) decrease anddecrease. |
176.An alternatoris deliveringcertain power at laggingp.f. andisconnectedto aninfinitebus. Ifsteam input to the turbine is increased, the p.f. and power angle respectively
(a) increase andincrease |
(b) increase and decrease |
(c) decrease andincrease |
(d) decrease anddecrease. |
177.A synchronous motor is taking certain amount ofpower at lag p.f. when connected to an infinitebus. Ifitsexcitationisincreased, thenp.f. andpower angleofthe motorrespectively.
(a) increase andincrease |
(b) increase and decrease |
(c) decrease andincrease |
(d) decrease anddecrease. |
178.A 1-<j>.transformerrated for 400/100 V, 1 kVA 50 Hz has load resistance of 100 ohm. The load resistance as viewedfromprimary side (400V) is
(a) 100 ohm |
(b) 25 ohm |
(c) 400 ohm |
(d) 1600 ohm. |
179. Buchholtz relay in a transformer is placedin between |
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(a) the LVwinding and the bushing |
(b) the tank andthe conservator |
(c) the HV winding and the bushing |
(d) the conservator and the breather. |
180.Thetransformerstampings are annealed before being used forbuildingthe core to
(a)reduce hysteresis loss due toburring ofedges
(b)reduce eddy currentloss due to burringofedges
(c)give mechanical strength to the core.
(d)increasecorepermeability.
181.The voltage regulation ofa transformer with negligible resistance and 10% reactance at
0.8p.f. lead is
(a) 6% |
(b) 8% |
(c) - 6% |
(d) - 8%. |
182.In a de machine, the polarity ofthe interpole is
(a)same as that ofthe main pole aheadforboth the generators and motors.
(b)same as that ofthe main pole behind for hoth the generators and motors.
REFERENCES
1. Langsdorf AS., Theory of alternating current Machinery, McGraw Hill 1955.
2.Wadhwa C.L., Network Analysis, New Age International Publishers 2004.
3.McPherson George & Laramore Robert D., An Introduction to Electrical Machines & Transformers John Wiley & Sons 1990.
4.Fitzgerald A.E. and Kingsley C., Electric Machinery 2nd edition McGraw Hill 1961.
5. V. Del Toro, Principles of Electrical Engineering Prentice Hall.
6.Golding E.W., Electrical Measurements and Measuring Instruments SIRISAC PITMAN & SONS 1960.
7.Hayt W.H. Jr. and Jack E. Kemmerly, Engineering Circuit Analysis McGraw Hill.
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