TOP MOST TRANSFORMERS - Electrical Engineering Multiple Choice Questions and Answers Electrical Engineering Multiple Choice Questions. Which of the following does not change in a transformer ?(a) Current(b) Voltage(c) Frequency(d) All of the above. Ans: c. 2. In a transformer the energy is conveyed from primary to secondary(a) through cooling coil(b) through air(c) by the flux(d) none of the above. Ans: c. 3. A transformer core is laminated to(a) reduce hysteresis loss(b) reduce eddy current losses(c) reduce copper losses(d) reduce all above losses. Ans: b. 4. The degree of mechanical vibrations produced by the laminations of a transformer depends on(a) tightness of clamping(b) gauge of laminations(c) size of laminations(d) all of the above. Ans: d. 5. The no- load current drawn by transformer is usually what per cent of the full- load current ?(a) 0. Ans: b. 6. The path of a magnetic flux in a transformer should have(a) high resistance(b) high reluctance(c) low resistance(d) low reluctance. Ans: d. 7. No- load on a transformer is carried out to determine(a) copper loss(b) magnetising current(c) magnetising current and loss(d) efficiency of the transformer. Ans: c. 8. The dielectric strength of transformer oil is expected to be(a) lk. V(b) 3. 3 k. V(c) 1. V(d) 3. 30 k. VAns: b. Sumpner’s test is conducted on trans- formers to determine(a) temperature(b) stray losses(c) all- day efficiency(d) none of the above. Ans: a. 10. The permissible flux density in case of cold rolled grain oriented steel is around(a) 1. ![]() ![]() Wb/m. 2(b) 2. 7 Wb/m. Wb/m. 2(d) 4. 7 Wb/m. Ans: a. 11. The efficiency of a transformer will be maximum when(a) copper losses = hysteresis losses(b) hysteresis losses = eddy current losses(c) eddy current losses = copper losses(d) copper losses = iron losses. Ans: d. 12. No- load current in a transformer(a) lags behind the voltage by about 7. The purpose of providing an iron core in a transformer is to(a) provide support to windings(b) reduce hysteresis loss(c) decrease the reluctance of the magnetic path(d) reduce eddy current losses. Ans: c. 14. Which of the following is not a part of transformer installation ?(a) Conservator(b) Breather(c) Buchholz relay(d) Exciter. Ans: d. 15. While conducting short- circuit test on a transformer the following side is short circuited(a) High voltage side(b) Low voltage side(c) Primary side(d) Secondary side. A varying current in the transformer's primary winding creates a varying magnetic flux in the transformer core and a varying magnetic field impinging on the secondary.Ans: b. 16. In the transformer following winding has got more cross- sectional area(a) Low voltage winding(b) High voltage winding(c) Primary winding(d) Secondary winding. Ans: a. 17. A transformer transforms(a) voltage(b) current(c) power(d) frequency. Ans: c. 18. A transformer cannot raise or lower the voltage of a D. C. Primary winding of a transformer(a) is always a low voltage winding(b) is always a high voltage winding(c) could either be a low voltage or high voltage winding(d) none of the above. Ans: c. 20. Which winding in a transformer has more number of turns ?(a) Low voltage winding(b) High voltage winding(c) Primary winding(d) Secondary winding. 2 Transformer technology at a glance An extensive transmission system with efficient transformers is indis-pensable to ensure a reliable supply of power. RealFastNews.com and RealFastNews.MOBi - The leading provider of PC and mobile news and video in Rome and Floyd County. Product specifications for the V28B28C150BL Mini DC DC Converter. Order direct from Vicor, manufacturers of power components and systems. 186 power transformer - standardisation manual 5 400/220/33 kv, 315 mva, 3Ø 185 - 230 14 - 18 road 6 400/220/33 kv, 500 mva, 3Ø 250 19 road / rail. Ans: b. 21. Efficiency of a power transformer is of the order of(a) 1. Ans: b. 22. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are(a) friction and windage losses(b) copper losses(c) hysteresis and eddy current losses(d) none of the above. Ans: c. 23. A common method of cooling a power transformer is(a) natural air cooling(b) air blast cooling(c) oil cooling(d) any of the above. Ans: c. 24. The no load current in a transformer lags behind the applied voltage by an angle of about(a) 1. In a transformer routine efficiency depends upon(a) supply frequency(b) load current(c) power factor of load(d) both (b) and (c)Ans: d. In the transformer the function of a conservator is to(a) provide fresh air for cooling the transformer(b) supply cooling oil to transformer in time of need(c) protect the transformer from damage when oil expends due to heating(d) none of the above. Ans: c. 27. Natural oil cooling is used for transformers up to a rating of(a) 3. VA(b) 1. 00. 0 k. VA(c) 5. 00 k. VA(d) 2. VAAns: a. 28. Power transformers are designed to have maximum efficiency at(a) nearly full load(b) 7. Ans: a. 29. The maximum efficiency of a distribution transformer is(a) at no load(b) at 5. Ans: b. 30. Transformer breaths in when(a) load on it increases(b) load on it decreases(c) load remains constant(d) none of the above. Ans: b. 31. No- load current of a transformer has(a) has high magnitude and low power factor(b) has high magnitude and high power factor(c) has small magnitude and high power factor(d) has small magnitude and low power factor. Ans: d. 32. Spacers are provided between adjacent coils(a) to provide free passage to the cooling oil(b) to insulate the coils from each other(c) both (a) and (b)(d) none of the above. Ans: a. 33. Greater the secondary leakage flux(a) less will be the secondary induced e. Ans: a. 34. The purpose of providing iron core in a step- up transformer is(a) to provide coupling between primary and secondary(b) to increase the magnitude of mutual flux(c) to decrease the magnitude of mag- netizing current(d) to provide all above features. Ans: c. 35. The power transformer is a constant(a) voltage device(b) current device(c) power device(d) main flux device. Ans: d. 36. Two transformers operating in parallel will share the load depending upon their(a) leakage reactance(b) per unit impedance(c) efficiencies(d) ratings. Ans: b. 37. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be(a) R2/VK(b) R2. IK2(c) R2. 2! K2(d) R2. KAns: b. 38. What will happen if the transformers working in parallel are not connected with regard to polarity ?(a) The power factor of the two trans- formers will be different from the power factor of common load(b) Incorrect polarity will result in dead short circuit(c) The transformers will not share load in proportion to their k. VA ratings(d) none of the above. Ans: b. 39. If the percentage impedances of the two transformers working in parallel are different, then(a) transformers will be overheated(b) power factors of both the transformers will be same(c) parallel operation will be not possible(d) parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load. Ans: d. 40. In a transformer the tappings are generally provided on(a) primary side(b) secondary side(c) low voltage side(d) high voltage side. Ans: c. 41. The use of higher flux density in the transformer design(a) reduces weight per k. VA(6) reduces iron losses(c) reduces copper losses(d) increases part load efficiency. Ans: a. 42. The chemical used in breather for transformer should have the quality of(a) ionizing air(b) absorbing moisture(c) cleansing the transformer oil(d) cooling the transformer oil. Ans: b. 43. The chemical used in breather is(a) asbestos fiber(b) silica sand(c) sodium chloride(d) silica gel. Ans: d. 44. An ideal transformer has infinite values of primary and secondary inductances. The statement is(a) true(b) false. Ans: b. 45. The transformer ratings are usually expressed in terms of(a) volts(b) amperes(c) k. W(d) k. VAAns: d. The noise resulting from vibrations of laminations set by magnetic forces, is termed as(a) magnetostrication(b) boo(c) hum(d) zoom. Ans: c. 47. Hysteresis loss in a transformer varies as CBmax = maximum flux density)(a) Bmax(b) Bmax. C) Bmax. 1- 8. 3(d) B max. Ans: b. 48. Material used for construction of transformer core is usually(a) wood(b) copper(c) aluminium(d) silicon steel. Ans: d. 49. The thickness of laminations used in a transformer is usually(a) 0. Ans: a. 50. The function of conservator in a transformer is(a) to project against’internal fault(b) to reduce copper as well as core losses(c) to cool the transformer oil(d) to take care of the expansion and contraction of transformer oil due to variation of temperature of sur- roundings. Ans: d. 51. The highest voltage for transmitting electrical power in India is(a) 3. V.(6) 6. 6 k. V(c) 1. V(d) 4. 00 k. VAns: d. In a transformer the resistance between its primary and secondary is(a) zero(b) 1 ohm(c) 1. Ans: d. 53. A transformer oil must be free from(a) sludge(b) odour(c) gases(d) moisture. Ans: d. 54. A Buchholz relay can be installed on(a) auto- transformers(b) air- cooled transformers(c) welding transformers(d) oil cooled transformers. Ans: d. 55. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds(a) 5. The main reason for generation of harmonics in a transformer could be(a) fluctuating load(b) poor insulation(c) mechanical vibrations(d) saturation of core. Ans: d. 57. Distribution transformers are generally designed for maximum efficiency around(a) 9. Ans: d. 58. Which of the following property is not necessarily desirable in the material for transformer core ?(a) Mechanical strength(6) Low hysteresis loss(c) High thermal conductivity(d) High permeability. Ans: c. 59. Star/star transformers work satisfactorily when(a) load is unbalanced only(b) load is balanced only(c) on balanced as well as unbalanced loads(d) none of the above. Ans: b. 60. Delta/star transformer works satisfactorily when(a) load is balanced only(b) load is unbalanced only(c) on balanced as well as unbalanced loads(d) none of the above. Ans: c. 61. Buchholz’s relay gives warning and protection against(a) electrical fault inside the transformer itself(b) electrical fault outside the transformer in outgoing feeder(c) for both outside and inside faults(d) none of the above. Ans: a. 62. The magnetising current of a transformer is usually small because it has(a) small air gap(b) large leakage flux(c) laminated silicon steel core(d) fewer rotating parts. Ans: a. 63. Which of the following does not change in an ordinary transformer ?(a) Frequency(b) Voltage(c) Current(d) Any of the above. RSI Home. Transmission Protection & Control. Distribution Protection & Control. Generator & Motor Protection & Control. Synchrophasor Measurement Systems. Communications Systems. Control House & Enclosure Solutions. Energy Storage Solutions. DC Critical Power Systems. 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