Question Bank in Transformers1. REE Board Exam April 1997 A single-phase transformer is rated 4,160-V primary and 250-V secondary. It has 1,500 turns in the primary and voltage regulation of 8%. What should be the number of turns in the secondary winding? A. 88 turns C. 90 turns B. 92 turns D. 86 turns 2. EE Board Exam April 1991 A certain transformer has a ratio of 8 is to 1. The primary winding resistance is 0.00283 Ω per turn and has 1,155 more turns than the secondary winding. If the copper loss in the primary is 20% less than the secondary, find the resistance of the secondary winding. A. 0.073 ohm C. 0.068 ohm B. 0.090 ohm D. 0.084 ohm 3. EE Board Exam October 1991 A 10-kVA; 2,400/240 V single-phase transformer has the following resistances and leakage reactances. Find the primary voltage required to produce 240-V at the secondary terminals at fullload when the load power factor is 0.8 lagging. r1 = 3 ohms x1 = 15 ohms r2 = 0.03 ohm x2 = 0.15 ohm A. 2,450 volts C. 2,496 volts B. 2,575 volts D. 2,632 volts 4. EE Board Exam April 1983 A single-phase transformer rated 75 kVA, 8000 volts primary and 240 volts secondary is given the short circuit test. With the secondary terminals short circuited, 440 volts (60 Hz) is impressed on the primary, which then draws rated current and 1125 watts. Solve for the percentage impedance of the transformer. A. 5.29% C. 5.50% B. 4.93% D. 5.13% 5. EE Board Exam April 1993 A short circuit test was performed upon a 10-kVA, 2300/230 volt transformer with the following results: Esc = 137 volts; Psc = 192 W; Isc = 4.34 A. Calculate in primary terms the reactance of the transformer. A. 31.56 ohms B. 29.88 ohms C. 10.19 ohms D. 12.45 ohms 6. EE Board Exam October 1984 A single-phase, 25 kVA, 4800/240 volt transformer was given the short circuit test. With the secondary terminals short-circuited, 93.75 volts was applied on the primary so that the ammeter reads rated current and the wattmeter reads 162.74 watts, all on the primary side. Solve for the percentage resistance of the transformer A. 1.95% B. 3.39% C. D. 3.02% 2.23% 7. EE Board Exam April 1990 The following data were obtained when a short circuit test was performed upon a 100 kVA, 2400/240 volts distribution transformer: Esc = 72 volts; Isc = 41.6 A; Psc = 1,180 W. All instruments are on the high side during the short circuit test. Calculate the equivalent resistance and reactance of the transformer. A. 0.682 ohm, 1.59 ohms B. 0.682 ohm, 1.73 ohms C. 0.752 ohm, 1.73 ohms D. 0.752 ohm, 1.59 ohms 8. REE Board Exam March 1998 A 13.8 kV/480 V, 10 MVA three-phase transformer has 5% impedance. What is the impedance in ohms referred to the primary? A. 0.952 ohm B. 0.03 ohm C. 5.125 ohms D. 9.01 ohms 9. EE Board Exam April 1990 B. The following data were obtained when a short circuit test was performed upon a 100 kVA, 2400/240 volts distribution transformer: Esc = 72 volts; Isc = 41.6 A; Psc = 1,180 W. All instruments are on the high side during the short circuit test. Calculate the percent regulation at a power factor of 0.75 lagging. A. 2.54% C. 2.62% B. 2.86% D. 2.71% 10. EE Board Exam October 1992 A 200-kVA transformer with impedance of 5% and the power factor of the load is 85%. The primary voltage is 6,000 volts while the copper loss is 5 kW. Find the percentage regulation. A. 5.03% C. 4.43% B. 5.21% D. 4.03% 11. EE Board Exam April 1993 A short circuit test was performed upon a 10-kVA, 2300/230 volt transformer with the following results: Esc = 137 volts; Psc = 192 W; Isc = 4.34 A. Calculate the percent regulation at a lagging power factor of 0.707. A. 5.28% C. 5.37% B. 5.55% D. 5.72% 12. EE Board Exam October 1992 In a 440 V, 50 c/s transformer, the total iron loss is 2500 W. When the supplied p.d. is 220 V at 25 c/s, the corresponding loss is 850 W. Calculate the eddy current loss at normal frequency and p.d. A. 2337 W C. 2010 W B. 2165 W D. 2216 W 55 watts D.3 pf lagging for 1 hour. hysteresis loss D. EE Board Exam April 1992 When the emf in the two windings of a transformer are opposite in direction.2 watts no load loss. 98.64% B. The maximum flux density is 10. October 1982 A 25-kVA distribution transformer operates at 120% load. 60 cycle transformer is tested in the laboratory so that its characteristics maybe determined.25 sec 21. 94. 2 sec D. REE Board Exam October 1997 A small single transformer has 10. cm. square of the frequency C. 97.5 A E = 230 V P = 187 W Short Circuit Test I = 21. The core has a volume of 750 cu. no saturation of core C.68% 17. not be affected by a change in the power factor B.52% D. square of the flux density 22. What is the fullload efficiency of the transformer at 0.5 sec B.45% D. EE Board Exam April 1995 Ideal transformer assumptions do not include A. 97. The length of time that a current of 20 times the rated current can be allowed to flow is A. 98. A. 2300/230 volts. and 10% load at 0. EE Board Exam October 1991 The copper loss of the transformer will A.55 watts B. increase with the lowering of the power factor 25.13.400/240 volts.80% 14.80 power factor? A. 5. EE Board Exam October 1993 A transformer is designed to carry 30 times its rated current for 1 second.3% C. Using the Steinmetz law to find the hysteresis.55 watts 23. 91.86% D.38% B. EE Board Exam April 1992 Given that the full load copper losses are exactly twice the iron losses in a 50 kVA transformer. the polarity is A. 98.23% C.53% C.12% D. art full-load.000 gauss and the -4 hysteresis constant of core is 5 x 10 . EE Board Exam April 1990 A 50 kVA. 91. 60-Hz transformer has a full-load power of unity over the period of 24 hrs. 2. increase with an increase of the power factor D.25% 15. EE Board Exam April 1995 The core loss of a 5 kVA single –phase transformer with normal voltage applied to the primary is 75 watts. The maximum efficiency occurs at 60% of full-load kVA. EE Board Exam October 1980.3% 18.86% 19.70% D. 94.9 lagging pf for 3 hours. EE Board Exam October 1990 Find the all-day efficiency of a transformer having maximum efficiency of 98% at 15-kVA at unity power factor and loaded as follows: 12 hours 2-kW at 0. 91. 0. subtractive 24.67 sec C. 93.5%. zero resistance of the winding D. determine the eddy current loss. The standard test requires an open circuit test and short circuit test. 3. The maximum efficiency is 95% and it occurs at full-load.8 leading pf for the rest of the day. 1. 2.5 pf lagging 6 hours 12-kW at 0. 96. Calculate the all-day efficiency if loaded as follows: 6-hours at full-load 6 hours at quarter load A. rheostat loss 26.8 pf lagging 6 hours at no load A. 2. 0.45% B. 97. A. negative B. EE Board Exam October 1991 A 30-kVA.55 watts C.37% B. 96. 93. 92. 89. 50% load at unity pf for 8 hours. REE Board Exam October 1998 Which of the following given below is the eddy current loss not proportional to? A. 93. Open Circuit Test: I = 6. 90. unity pf. 0. eddy current loss C. what is the all-day efficiency of the transformer? A.6% B. decrease with a lowering of the power factor C.48% C.7 A E = 115 V P = 570 W Determine the efficiency of the transformer at half load. additive D. EE Board Exam June 1990 Power lost due to alternating magnetization and demagnetization of the core material A. and that the quarter load efficiency is 96. 92. If core loss is 150 watts and full load copper loss is 500 W.16% C.14% B. zero reactance of the winding 20. 97. square of the load current of the laminated core D. copper loss B. EE Board Exam June 1990 . A. 95. 4.7% D. square of the thickness B. 97. no leakage flux B.55% C. 95. positive C.36% 16. calculate the full load efficiency at unity power factor. current loss C.78 x 10 ohm -5 D. EE Board Exam April 1990 When the primary and secondary windings take the form of a common ring which is encircled by two or more rings of magnetic materials distributed around its periphery. the transformer is termed as A. grounding transformer B. primary winding C. EE Board Exam April 1991 A certain transformer has a ratio of 8:1. in-phase with each other D.00283 Ω and has 1.78% D. A transformer having 1000 primary turns is connected to a 250-V a. A. determined by load on transformer secondary 40. 13. anti-phase with each other C. simplify its construction minimize eddy current loss reduce cost reduce hysteresis 38. voltage B. The primary winding resistance is 0.400/240 volts. The primary and secondary windings of an ordinary 2-winding transformer always have A. frequency voltage current voltage and current 34. mutual flux 35. Which of the following is not a basic element of a transformer? A. separate magnetic circuits .c supply. 78. 8. C.18 x 10 ohm 29. C. hysteresis loss D. 5. autotransformer connection D. EE Board Exam June 1990 Which transformer has only one winding? A.000 volts while the copper loss is 15 kW. 250 D. D. 2. decrease reluctance of the common magnetic circuit 37. Find the percentage voltage regulation. In an ideal transformer A.45% 28. eddy current loss B. The primary voltage is 6. B. 23. D. Scott or T-connection B.49% C. The primary and secondary induce e. For a secondary voltage of 400 V. core loss 27.91% B. The maximum efficiency is 95% and it occurs at full-load. 92.90% C. 400 B. A transformer transforms A. wye-delta connection 31. 1250 39. open delta C. different number of turns B. The main purpose of using core in a transformer is to A. If the copper loss in the primary is 20% less than the secondary. C. Transformer cores are laminated in order to A.fs. regulating transformer C. autotransformer D.53 x 10 ohm -4 B. current C. EE Board Exam October 1991 A 30-kVA. the number of secondary turns should be A. EE Board Exam October 1992 A 200-kVA transformer has an impedance of 15% and the power factor of the load is 85%. E1 and E2 in a two-winding transformer are always A.38% D. same size of copper wire C. 60-Hz transformer has a full-load power of unity over the period of 24 hrs. D. A. shell type transformer 33. Core B. B. equal in magnitude B. secondary winding D.In the open circuit test of the transformer the wattmeter reading is equal to A. a common magnetic circuit D. eliminate magnetic hysteresis D. B. 4.67% B. -5 A. distribution transformer B. EE Board Exam June 1990 Transformer connection that can transform threephase system to two-phase system and vice versa A.56 x 10 ohm -7 C. 88. windings have no resistance core has no losses core has infinite permeability all of the above 36. A step-up transformer increases A. power transformer C. 6. isolated winding transformer 32.165 more turns than the secondary winding. 15. decrease iron losses B. power frequency 41. 2.67% 30. Calculate the all-day efficiency if loaded 6-hours at full-load. 1600 C. 89. calculate the resistance of the secondary winding. core type transformer D.m. prevent eddy current loss C. D. In operating a 400 Hz transformer at 50 Hz A. requires least voltage to perform the test C. No-load test on a transformer is carried out to determine A. 100 53. 640 D. low voltage side is usually short circuited C. it has become customary 56. D. 0. D. transformer efficiency is low because A. side of a transformer during short-circuit test is 2% of its rated voltage. The iron loss of a transformer at 400 Hz is 10 W. equal to D. A. B.m. fixed loss is high in proportion to the output . leakage paths do not saturate C.v. A. A transformer has negative voltage regulation when its power factor is A. the leakage flux of each winding is proportional to the current in that winding because A. supply frequency is held constant 52.1 ohm when referred to secondary becomes ____ ohm. primary current is 20 times greater than the secondary current D. In performing the short circuit test of a transformer A. greater than 44. iron core becomes fully saturated D. equal to K times B. In a two-winding transformer. 0. kVA is fixed whereas kW depends on load p. The equivalent resistance of the primary of a transformer having K = 5 and R1 = 0. any side is short circuited with preference D. Assuming that eddy current and hysteresis losses vary as the square of flux density. the ratio 20:1 indicates that A. the entire input is just sufficient to meet Cu losses only B. When a 400 Hz transformer is operated its kVA rating is A. core loss C. 4 C. The main purpose of performing open-circuit test on a transformer is to measure its A. secondary voltage is 1/20 of primary voltage C. unity C. The core loss will be ____ percent of the rated core loss. total loss D. Transformers are rated in kVA instead of kW because A. reduced to 1/8 B. total transformer loss depends on voltampere D. power turn in primary. draws sufficiently large no-load current for convenient reading B.f. leading lagging 48. During short-circuit test. 1. for every 20 turns on primary.42.5 47. there are 20 turns on primary one turn on secondary th B. A. magnetizing current and no-load loss D. the two windings are electrically isolated D.25 B. secondary output is low B. In a transformer. per turn in secondary winding is always ____ the induced e. The primary reason why open-circuit test is performed on the transformer is that it A. increased 64 times 57. C. 2. magnetizing current C. unaffected D. only voltage is reduced in the same proportion as the frequency only kVA rating is reduced in the same proportion as the frequency both voltage and kVA rating are reduced in the same proportion as the frequency none of the above 54.f. insulation resistance 51. equal to 1/K times C.02 D. mutual flux is confined to the core 43. transformer losses are high C.04 55. increased 8 times C.m. A.5 C. Ohm’s law applies to magnetic circuits B. the e. needs minimum power input D.f. load power factor is often not know B. 0. 80 C. the iron lose of a transformer is negligible because A. 0. zero B. At relatively light loads. involves less core loss 49. 0. In relation to a transformer. Cu loss B.4 D. high voltage side is usually short circuited B. C. The voltage applied to the h. efficiency of the transformer 50. 0. the iron loss of the transformer at rated voltage but 50 Hz would be ____ watt.25 B. there is one turn on secondary 45.004 B. copper loss B. flux produced is a small fraction of the normal flux C. none of the above 46. 173. The marked increase in kVA capacity produced by connecting a 2 winding transformer as an autotransformer is due to A.3 D.60 kVA B. A. An autotransformer having a transformation ratio of 0. 75 B. 2. A.05 C.25 is ____ ampere. Its load kVA corresponding to maximum efficiency is ____ kVA.600/400 volts 60 cycle single phase core type transformer has the following average daily load: Full-load at 0. both B and C 64. The output current corresponding to maximum efficiency for a transformer having core loss of 100 W and equivalent resistance referred to secondary of 0. 100 C. The power transferred conductively from primary to secondary is ____ kW.25 kVA . voltage D. 2. 2. A. share the load unequally B. Cu loss of 1600 W occurs at ____ kVA. 375 B. The saving in Cu achieved by converting 2- winding transformer into an autotransformer is determined by A. it runs at full-load C. voltage transformation ratio B. EE Board Exam October 1991. 0. 1. 5 B. its copper loss B. A.4 59. 150. EE Board Exam June 1990 What should be the KVA rating of each two transformers in an open-delta bank when the three-phase balanced load is 290. 0. the amount of load C. size of the transformer core 67. increase in transformer efficiency D. The all-day efficiency of a transformer depends primarily on A.707 pf for 10 hours No-load for 6 hours Calculate the ratio of full-load copper loss to the iron loss for the transformer to be most economical for the above loading. 25 Unsolved problems 71. transformation ratio is increased B. 20 C. If Cu loss of a transformer at 7/8th full-load is 4900 W. the two transformers will A.6 C. increase in turn ratio B. magnetic quality of core material D.09 D. 155. have a circulatory secondary current even when unloaded D. A.5 B. 25 D. percentage impedance 69. 5600 C. its Cu loss equals iron loss D.L. A.8 pf for 8 hours Half-load at 0.D. A. it runs at half full-load B. 177. establishment of conductive link between primary and secondary 65. 56. 3. 400 62. 50 B. The kVA rating of an ordinary 2-winding . The maximum efficiency of a 100-kVA transformer having iron loss of 900 kW and F. then its full-load Cu loss would be ____ watt. 6. energy is transferred both inductively and conductivity D.8 supplies a load of 3 kW. 33 B.27 68. If the impedance triangles of two transformers operating in parallel are not identical in shape and size. the duration of load D.28 THREE PHASE TRANSFORMER CONNECTIONS 72. kVA rating C.4 kVA? A. transformer is increased when connected as an autotransformer because A. secondary current is increased 66. polarity B.4 D.40 kVA C. April 1994 A 1000 kVA.3 C. load on the secondary C. get heated unequally C. Two transformers A and B having equal outputs and voltage ratios but unequal percentage impedances of 4 and 2 are operating in parallel. Transformer A will be running over-load by ____ percent. secondary voltage is increased C. 50 C. 200 D.17 B. 429 60. 6400 D. 133. increase in secondary voltage C. A 200 kVA transformer has an iron loss of 1 kW and full-load Cu loss of 2 kW. run with different power factors 70. The essential condition for parallel operation of two 1-φ transformer is that they should have the same A. 2. 66 D.7 63. The ordinary efficiency of a given transformer is maximum when A. it runs slightly overload 61. Cu loss is small 58. 141. 5% B.70 pf lagging. 84.4% 82.80. 20 75.866 pf lagging. A. 25 C. 112 kW D. 60 Hz. A.54 kW at 0. 167. considering that the load has a power factor of 0.87 and 6. 130.73 kVA B.5 kW C. EE Board Exam April 1983 Two single-phase transformers are connected in V-V (open delta) and serving a delta connected impedance load with each impedance equal to ohms. 3-phase induction motor. EE Board Exam April 1981 A V-V or open delta connected transformer bank. A.24 81. 73.5 pf and 23. Solve for the minimum size in kVA of each transformer needed to supply the power without being overloaded.90 efficiency.5 pf and 22.85 lagging. 170. EE Board Exam October 1985. EE Board Exam October 1980 Two identical 1-phase transformers connected in open delta will serve a 3-phase motor lad of 250 hp. 79.61 C. 0. 30 kVA C.4 kVA. 9.5 kVA.13 79. If each transformer is rated 75 kVA capacity. 23 B.8 lagging power factor. EE Board Exam April 1985 Two single-phase distribution transformers are banked in V-V (open delta).707 pf D. If the transformer voltages impressed on the transformer are: V V Solve for the kVA delivered by each transformer. 130 kW B.84 and 5. 8. EE Board Exam April 1980 Two single-phase distribution transformers connected in open delta will supply power to a 200 hp. EE Board Exam April 1985 A balanced 3-phase transformer bank has deltaconnected primary and secondary windings. If each transformer is rated 37. 5. The primary to secondary winding voltage ratio is . 12. 53.28 and 5. 8 kVA C.25 kVA 74. 136. 150.33 C. 114 kW 78. solve for the maximum 3-phase load that the bank can carry without overloading. If a third transformer is added for delta operation. EE Board Exam April 1986 A V-V (open delta) connected transformer bank serves a balanced 3-phase load of 40 kVA at 230 V and 0. 52. April 1986 An open-delta connected transformer bank serves a balanced 3-phase load of 40 kVA at 230 V and 0.6 kW B.64 D. 94 turns and 83 turns B.66 kVA 73. 93 turns and 84 turns C. what is the maximum 3-phase load in kilowatts that the bank can carry without suffering overload considering that the load has a lagging power factor of 0. A. 92 turns and 85 turns 84.6% D. If one transformer is removed for repairs. 185.70 power factor and 0. 160.09 kW at 0. 12. If there are 1500 turns on the 2-phase side.43 B.38 kVA D.90 efficiency. 129. 104 kW C.54 kW at 0.2% C. 80. EE Board Exam April 1992 A 6600-volt. 6.91 D. 2-phase network is connected to a three-phase. 25 kVA 83. A.24 and 6. Voltage per phase on the 3-phase side is 240 V. EE Board Exam October 1983 Three single-phase transformers each rated 75 kVA are banked in delta and supplying a 3-phase load drawing 160 kVA at 0.22 kW at 0.09 kW at unity pf B. Solve for the real power and p at which each transformer is operating.707 pf 80.866 pf lagging. A. EE Board Exam June 1990 Two single-phase transformers in an open delta bank served a three-phase balanced load of 290. 20 kVA B.42 at unity pf C. 55. what percent increase in load does this represent? A. 124.45 kVA C.866 pf and 23.866 pf and 22.D. Solve for the minimum size in kVA of each transformer required to serve the load without overloading. solve for the amount of overloading of the remaining units. 95 turns and 82 turns D. 11. EE Board Exam October 1986 The Utility Company supplies two single-phase transformers banked in open delta. 10 kVA D. calculate the number of turns on the 3-phase side required for the main and teaser transformers. A. 16 kVA B. Solve for the minimum kVA of each transformer needed to accommodate the load without overloading. 6. 24 D.24 kVA D. Solve for the minimum size in kVA of the transformers needed. 49.48 kVA 77. 0.22 kW at 0. operating at 0. 7. 4-wire system by a Scottconnected transformer combination. A.2 kW 76. composed of two identical units serves a balanced 3-phase load of 16 kVA at 230 volts. A.429 kW at 0.5 kW D. A. 11.20 B. 5 ohms.5 kV/13. B = 157 kW B.50 kVA. A. 115 A D. How much load does each carry? A. 1725 A D. 80 . Calculate the power delivered by each transformer. 50 kVA. A voltmeter connected line to ground reads 66 volts. 1207. 52 kVA.3 A.7 kV C. 200 A C. What is the kV rating of the secondary winding? A.2 kV D. A = 127 kW. Determine the full load phase current on the secondary side.000/66.78 kVA. 175 A 85. Transformer A is rated 100 kVA with equivalent impedance of 9. What is the voltage of the line? A. 1725.7 A. EE Board Exam October 1981 Two distribution transformers are connected in parallel supplying a load of 125 kVA.2400/277. 97 C.000 kVA from 230 kV to 4160 V if the transformer is to be connected Δ – Y? A. What is the multiplier of the kW hr and demand meters? A. Transformer B has a resistance of 2% and a reactance of 5%. Current transformers with ratio of 200/5 are use to meter the electrical usage. 220.76 kV/66.4 A B. If transformer A is rated 50 kVA. 112.000 kVA.5 kVA B.8 lagging pf. what is the transmission line voltage? A. 1449.5 kVA 94. 88 kW. Solve for the loading of each transformer. 40 C. The voltmeter connected at the secondary reads 64 volts.375 V are connected wyewye.8 89. 73 kVA 93. 83 kW. 92 kW D. REE Board Exam October 1997 A power transformer rated 50.9 D. 98 D. EE Board Exam April 1993 MERALCO has two single-phase transformers with equal turns ratio and ratings are operated in parallel to supply a load of 280 kW at 0. B = 153 kW 95. B = 158 kW D. 77. 135. 23. 67 kVA D. 94 C. 87. 525. 100 D. 80. 221.8 kV is connected wye-wye. 483. with 14 ohms equivalent reactance and transformer B is rated 75 kVA with 11 ohms equivalent reactance. A = 125 kW. 96 B. 1449 A B. 55 kVA. Transformer B has a resistance of 1% resistance and a reactance of 6%.5 kV/13. 34. 132 kV 87. 78. 10 MVA three-phase transformer is connected wye-grounded delta. 79 kW. Find the kVA load of each transformer.7 A D. EE Board Exam October 1985 Two transformers are connected in parallel to supply a common load of 175 kVA. A. B = 155 kW C. REE Board Exam March 1998 A 125 kVA distribution transformer with 4% impedance is connected in parallel with another transformer rated 75 kVA and with 35% impedance. 2092 A C.2 A 91. 76. A. 34. 99 D. 97 86. 59.5 kVA. 2092 A C. 1208 A 88. EE Board Exam October 1991 What should be the turns ratio of a three-phase transformer to transform 10. 52. A = 122 kW. 60 kVA D. What are the line currents at full load? A.90.10 kV D.5 A. 100 92.25 kV 90. Determine the power delivered by the transformers A and B to the load. 225. 80. 200 B.22 kVA C. 7. REE Board Exam March 1998 A power customer draws power at 220 volts from a transformer on a pole. REE Board Exam April 1994 Two single phase transformers with equal ratings and turns ratio are operated in parallel to supply a load of 180 kW at a lagging pf of 0. 836. 150 A B. 97 kW B. 75 kVA C. Solve for the primary line current if the low-side (secondary) load draws a line current of 1000 A. 3623. REE Board Exam October 1998 The potential transformer of a line has a ratio of 132.000 kVA. A. REE Board Exam October 1997 The PTs of a 220 kV transmission line have a ratio of 132. 13. A. REE Board Exam October 1998 A 69/13. These are connected wye-delta.63 kV C.) The total load is 140 kVA at 85% power factor. 15 B. 80 kVA.15 kV B. Transformer A has a resistance of 2% and a reactance of 8%. 100 kW 96.8 kV is connected wye-grounded primary and delta on the secondary. (Neglect resistance of each transformer. 80 kW. 70 kVA B.97 C. Transformer A has a resistance of 1% and a reactance of 6%. A.6 ohms while transformer B is rated 75 kVA with equivalent impedance of 12.1 A. 92 kW C. A = 123 kW. 95 B. 75. REE Board Exam October 1997 A power transformer rated 50.8 kV. 58 kVA. 228. 223. 62.5 kV B. Both have same voltage ratio. 1. A capacitor and an inductor D. 40 D. 20 105. 140 turns in the primary and 7 turns in the secondary.5% taps below the rated voltage. 525.5%? A. EE Board Exam April 1988 Two single-phase transformers each rated 75kVA are connected in V-V or open-delta.207. determine the size of the capacitor in kVAR. REE Board Exam March 1998 A 50 MVA. sectionalizer C.10% and 900 V load output. wye-delta connected transformer has a 3% impedance.133 turns C. 12 V C. 15 MW 98.56% 99.7 amperes D.5° A C. 900 V 108.2 MW B. 1. surge arrester D. to step down current 102. 4. A parallel resonant circuit C. what are the line currents at full-load? A. 7.5 kV/13. primary voltage is 240 Volts. REE Board Exam October 1997 A power transformer is rated at 50. tertiary transformer 101. ECE Board Exam April 2001 How much is the secondary voltage of a power transformer whose parameters are as follows. REE Board Exam October 1996 A three-phase transformer has a primary voltage rating of 34. 4. 2. 0. One D.9 V B.21 cis -30° A D.5% taps above and two 2. A. 34. 5. to provide path to zero sequence currents C. 3. 2.74% B. The secondary winding is rated 460 volts and is delta connected.2 amperes 103. the PT ratio is 1000 and the CT ratio is 1200/5. REE Board Exam October 1997 At a 155 kV substation. ECE Board Exam April 2001 A transformer composed of two or more coils which are wound around a non-metallic core A. 5.1 amperes. A.7 amperes.449. 1. ECE Board Exam April 2000 It is a transformer with two or more windings on a laminated iron core used to supply stepped up or . 483. The potential going into the wattmeter is 115 volts. 6 V B. to serve a three-phase load of 120 kW at 0.312 turns D. To prevent the overloading of transformers. 36 V 110. 999.092 amperes C. 24 V D.2 amperes. 50 C.333 turns 104. A. REE Board Exam September 2001.97. October 1998 The loads of a wye-connected transformer are: Ia = 10 cis (-30°) A Ib = 12 cis 215° A Ic = 15 cis 82° A What is the neutral current? A. ECE Board Exam April 1998 A transformer consists of the following? A.04 cis 72.49% D. If it has 100 turns. ECE Board Exam April 1999 An autotransformer contains how many coils? A.11 cis 72. three-phase. 90 V D.80 power factor lagging. Air core transformer 106.3 amperes. ECE Board Exam April 2000 Find unloaded output of a power supply having a transformer regulation of 11. 1. Iron core transformer D. what will be the effective number of turns in the primary winding if voltage tap us set at minus 2. REE Board Exam October 1998 Its primary function is to provide ground source A.8° A B. Free core transformer C. 99.725 amperes B. zigzag transformer B.99 V C. 3. What is the MW indicated when the wattmeter reads 800 watts? A. None C. REE Board Exam October 1997 What is the main use of a zigzag transformer? A. Metallic core transformer B.639% C. 19. 1. Two B. 33 kV/11 kW. What is the %impedance at 100 MVA base and 34. wye-connected with two 2. 30 B. 836. 150 MW D.222 turns B.8 kV is connected wye-wye. 7.623. 192 MW C. to stabilize transformer sequence currents D.92 cis 62. to step down voltage B. Two coils wound on a common core 109.5 kV. An inductance and resistance B.5 kV base? A.8° A 100.000 kVA. 6. Three 107. Secondary winding D. Leakage resistance B. A transformer does not possess ____ changing property. ECE Board Exam April 1999 The current that flows in the primary of a transformer with the secondary open (or no load is attached). current power . impedance B. A step-down transformer D. A. Step up transformer D. D. A. Metallic core transformer B. Core C.c. Stray capacitance D. The winding of the transformer with greater number of turns will be ____. A.c. Iron core transformer 118. either high or low voltage winding D. a. as well as d. Exciting current C.stepped down values of voltages to various circuits of an equipment. low-voltage winding C. A. An autotransformer 112. A. Air core transformer D. Self-inductance C. AF transformer 111. Load current D. D. B. ECE Board Exam April 2001 A transformer composed of two or more coils which are wound around a non-metallic core A.c. only C. 12 volts 113. less than C. is a static device B. Autotransformer D. A transformer is an efficient device because it ____. 6 turns for secondary and 120 volts for secondary voltage. Coupling current 114. Free core transformer C. 60 volts D. electrically magnetically electrically & magnetically none of the above 120. frequency C. voltage B. The voltage per turn of the primary of a transformer is ____ the voltage per turn of the secondary. Step down transformer C. 6 volts B. Source current B. ECE Board Exam April 1996 What type of transformer that is used to protect technicians and operates from deadly electrical shock? A. uses electric coupling 121. ECE Board Exam November 1998 Which of the following does not contribute to losses in a transformer? A. A step-up transformer B. none of these 123. ECE Board Exam November 2001 Find the primary voltage of a power transformer under the following conditions 3 turns for primary. only B. A transformer will work on ____. high-voltage winding B.c. A. the same as D. Iron losses 117. time period 122. none of the above 124. A. Absorber transformer B. C. d. The primary and secondary of a transformer are ____ coupled. A transformer transfers electrical energy from primary to secondary usually with a change in ____. Primary winding 116. Isolation transformer 115. voltage C. 8 volts C. more than B. Enclosure B. uses capacitive coupling C. A. An isolation transformer C. uses inductive coupling D. RF transformer B. Power transformer C. A. none of the above 119. ECE Board Exam November 2000 Components of the transformer which receives energy from the primary winding and delivers it to the load. ECE Board Exam April 1999 A transformer with 100 turns in the primary winding and 25 turns in the secondary winding is which of the following? A. power D. A. a. A. D. supply. inversely proportional to supply frequency C. ____. D. primary draws small current B. The no-load input power to a transformer is practically equal to ____ loss in the transformer. then ____. both primary and secondary winding D. then ____. C. purely alternating one purely rotating one partly alternating and partly rotating none of the above 129. A. provide tight magnetic coupling C. reduce core losses D. directly proportional to supply frequency B. does not work C. good electric coupling 130. iron losses component of Io is large magnetizing component of Io is large magnetizing component of Io is small none of the above 134. none of the above 128. currents and induced voltages D. 125. iron B. A. A. If a transformer core has air gaps. primary reactance is too much increased B. A. ampere-turns and voltage per turn B. iron core has high permeability B. primary leakage reactance is increased C. inversely proportional to primary voltage D. hysteresis loss is decreased C. none of these 135. B. none of the above 136. none of the above 132. of a transformer is small because ____ A. none of the above 139. C. reluctance of magnetic path is decreased B. The iron-core is used to ____ of the transformer. core losses will be excessive D. applied voltage is sinusoidal D. primary winding only B. The primary leakage flux links ____. secondary winding only C. C. none of the above 137. none of the above 126. air is not good magnetic insulator C. copper C. increase copper losses decrease copper losses cause voltage drop in the windings none of the above Leakage flux in a transformer occurs because ____. has the same number of primary and secondary turns D. A. An ideal transformer is one which ____. A. A. permeability of core is increased B. B. The effect of leakage flux in a transformer is to ____. B. resistance and leakage reactances C. above 40% The no-load p.f. primary may burn out 131.133. increase the weight B. A transformer operates poorly at very low frequencies because ____. tight magnetic coupling D. A. eddy current is increased 127. A. A. A. A. A. primary will draw large power C. A transformer is so designed that primary and secondary have ____. The flux in the core of a single-phase transformer is ____. eddy current D. A. 30 – 40% B. D. A. 140. high leakage flux B. magnetizing current is abnormally high C. Two things which are same for primary and secondary of a transformer are ____. transformer is not an efficient device . magnetizing current is greatly increased D. large resistance C. has no losses and leakage reactance B. The maximum flux produced in the core of a transformer is ____. primary reactance is too much increased D. 3 – 5% C. The no-load primary current Io is about ____ of full-load primary current. none of the above 138. D.c. 15 – 30% D. When the primary of a transformer is connected to a d. If a power transformer is operated at very high frequencies. core losses are increased D. measuring C.2 50 .5 kVA and 62. Y – Y D. 0. 34.26% D. 106.8Y kV and 2% impedance. The transformers have secondary voltages of 220 volts and same voltage ratio. 73.000 kVA.2 Ω D. 82. 1. determine the kVA sharing of each transformer.6 153. what is the relay impedance to protect the line from fault? A. Determine the percent (%) voltage drop at the secondary at 80% load and at 75% power factor. 2. 0. As compared to – bank. 66.5 kVA 147.141. If the common load is 125 kVA at 80% p.7 C.8 kV. 50 B. REE Board Exam October 1997 A 3-phase transformer is rated 30 MVA. 86. A.6% C. 7. D. If the impedance of each line is 10 Ω.7 D. A. What is the secondary line current? A. A.f. Y – 151. What is its impedance at 100 MVA base? A. neutral is fundamental to the A.2 D. The mutual flux in a transformer remains constant at all loads because ____. –Y B. 4wire service? A.52 A C. suppression of harmonies B.7 C. Transformer 1 is rated 100 kVA with 4% reactance while transformer 2 is rated 75 kVA with 3% reactance.5 MVA transformer has 8% impedance.000 Ω B. Cores of large transformer are built up to nearly circular crosssection in order to reduce ____. 48.87 kV autotransformer has 200 A current in the common winding. 62.1% C. REE Board Exam October 2000 The CT ratio and PT ratio used to protect a line are 240 and 2000 respectively.05% B. 86.75% impedance. sensing 145. – C. lagging.2 148. 0. losses are small 142. increase in a capacity of the system is ____ percent. A. provision of dual electric service D. copper loss Unsolved problems 143. 115Δ/13. leakage flux is small C. 83. 143.48 A B. 73. 1. eddy current loss D.57 kVA B. 800% B. detecting D. 0. 4. balancing of phase voltages with respect to line voltages 152.7 C. the capacity of the V – V bank of transformers is ____ percent.15% 150. 66. REE Board Exam October 2000 Two single-phase transformers operate in parallel. 58 154. applied voltage and frequency are constant B. 173.2 B. Which of the following connection is best suited for 3-phase. 66. the resistance is negligible compared with the reactance. leakage reactance B. relaying B. they are used for A.0635 C. 57. 200 A D. 34.0575 B.33 Ω C. 3. 75 kVa and 50 kVA C.43 kVa and 53. What is the per unit impedance? A. REE Board Exam April 2004 Instrument transformers are used in indicating and metering and with protective devices. If three transformers in a – are delivering their rated load and one transformer is removed. REE Board Exam September 2002 A 20 kV/7. A.6 B. April 2004 REE Board Exam A transformer rated 2.5 kVA and 42. iron-core is used D.5 kVA D. 329 A 144. In a three-phase Y – Y transformer connection. 71. A. A.0656 D. then overload and each of the remaining transformer is ____ percent. 56. REE Board Exam April 2001 A 69 kV/13. 8% D. 12 Ω 146.7% 149.500/240 volts has 5. iron losses C. passage of unbalanced currents due to loads C. When a V – V system is converted into a – system. 0. then the average p.2 157. Reason. all of the above 165.f of the V-bank is A. transformer is made of A. D. The core of a transformer is assembled with laminated sheets to reduce A. load power factor is leading C. annealed copper C.75 C. excessive heating of the core B. increase the efficiency B. A T – T connection has a higher ratio of utilization that a V – V connection only when A.bank. transformers must have equal 161. transformers must be operated at the same frequency D. Before removing the ammeter from the current transformer. The biggest advantage of T – T connection over the V – V connection for 3-phase power transformation is that it provides A. seasoned copper D. all of the above 166. statement is correct. increases the no-load power factor angle 169. Scott B. A. magnetizing current 168. a true 3-phase. 23 D. star/star C. transformers must have same ratio of transformation C.c. – 164.6 B. A. 57. An auto-transformer is more efficient in transferring energy from primary to secondary circuit.7 C. more voltages 160. 0.load of 40-kVA. Cooling of transformers is necessary to A. 66. dissipate the heat generated in the windings C. star/double-delta 163. increase in iron losses D. AT–T transformer cannot be paralleled with ____ transformer. reason is correct and relevant B. both statement and reason are false 162. hysteresis loss B. both statement and reason are correct and are connected to each other as cause and effect D.51 0. magnetic noise D. One of the following statements concerning parallel operation of transformer. Each of the two remaining transformer supplies ____ percent of the original load.886. 73. eddy-current loss C. Y – Y B. should be nearly ____ kVA. is 0. silicon steel B. reason is correct but irrelevant C. load power factor is unity D. 4 wire system C. Key A. aluminum The core of a 167. For supplying is a balanced 3. Because it does so both inductively and conductively. A. Out of the following given choices for polyphase transformer connections which one will you select for threeto-two phase conversion? A.886 B. its secondary must be short-circuited in order to avoid A. 34. high secondary emf C. reduces magnetizing current B.65 158. non-identical transformer are used 159. Instrument transformers are used in a. If the load p.155. 25 156. 0. double Scott D. wattmeters D. a higher ratio of utilization D. V – V C. reduce the losses . statement is false. the one which is not correct is A. 20 C. Y – D. ammeters B. rating of each transformer in V – V bank. When a closedbank is converted into an open. The use of grainoriented laminated sheets in building a transformer core A. a set of balanced voltages under load B. identical transformers are used B. reduces hysteresis loss D. voltmeters C. Statement. reduces eddy-current loss in the core C.f.7 D. transformers have equal voltage ratings B. 50 B. circuits for extending the range of A. Copper Loss = 180 W D. 55% 175.5% D. A. B. The cross-sectional area of the core is 2 2 A. The percentage impedance of the two transformers should be equal. A 100-kVA. reduce humming 170. What is the voltage regulation of the load? A. the terminal voltage became 11550 V.33% D. 1100/440-V. 11.25 Tesla.67% B. the transformers should have the same kva ratings D. the transformers should belong to the same vector group B. Copper-losses and core-losses respectively C. The maximum flux density in the core of a 3000/240-V. Core loss = 320 W. When the load was switched off. Indicate which of these is not required to be fulfilled. The ratio of the primary to secondary voltage of a transformer is 2:1. Core loss = 320 W. 550 C. Maximum efficiency of a transformer occurs when A. 50 Hz singlephase distribution transformer is 1. Load = 40 kVA. be out-of-phase with the core flux D. 97% 179. kVA ratings of the two transformers should be equal B. Hysteresis loss and eddy-current loss respectively 176. 5. Core loss = 320 W. power factor of the load is leading D. Load = 20 kVA. be independent of the core flux 171. D. hysteresis loss is equal to eddy-current loss 177. the transformers should not belong to the same vector group 181. 375 C. Eddy-current loss and hysteresis loss respectively D. 5% B. The number of turns in the primary will be A. C. A transformer when supplying a load maintained 11 kV across terminals. The emf induced in the secondary winding of a 50-Hz single-phase transformer having 100 turns on its secondary is 222 V. A. 180. 0. Copper Loss = 80 W 174. 2750 B. Core-losses and copper losses respectively B. The all-day efficiency of a transformer is the ratio of A. At what load will the efficiency of the transformer be a maximum? A. 362 . 0. Transformers should be properly connected with regard to their polarity C. The saving in terms of weight of copper required if an autotransformer is used instead of a two-winding transformer will be A.01 m D.D. The copper-loss and core-loss of a transformer of a transformer at various loads are as shown below. The turns ratio of the transformer should be equal. The maximum flux density in the core is 2 0. 275 D.1 Wb/m . A number of conditions are written below. Copper Loss = 500 W B. 292 B.55% C.001 m 173. Load = 50 kVA. 1 m 2 2 B. 66. 288 D. determine the 2 cross-sectional core in cm . The emf induced in the windings of a transformer will A. Load = 30 kVA. hysteresis loss and eddy current loss are minimum B. kWh output and kWh input per day kWh output and kWh input in a day output power and input power input power and output power 178. 50-Hz single-phase transformer has 100 turns on the secondary winding. Power lost in the open-circuit and shiort0-circuit tests on a transformer gives approximately an account of the following losses: A. Copper Loss = 320 W C. For satisfactory parallel operation of two single-phase transformers a number of conditions are to be fulfilled. Core loss = 320 W. ratios of winding resistances to resistances for the transformers should be equal C. Voltage ratings of the primary windings should be suitable for supply system voltage and frequency. lag the core flux by 90 degrees B. D. the sum of hysteresis loss and eddy current loss is equal to copper loss in the windings C. 5500 172. 0. 50% C. An additional condition for parallel operation of three-phase transformers over single-phase transformers is that A.1 m C. be in-phase with the core flux C. 33. If the voltage induced per turn is 8 volts. 60 mWb D. A. The special silicon steel is used for laminations because A. B. The frequency is 60 Hz. at power factor below a particular value D. electric circuit magnetic circuit winding wire gauge none of the above 195. D. Preferably. D. frequency B. 7. low or high depending upon whether it is step up or step down respectively D. low resistance 189. low carbon steel B. _____current are wasteful currents which flow in cores of transformers and produced heat. C. The low side of a certain welding transformer has 2 turns and delivers 300 A. C. hysteresis losses are reduced eddy current losses are reduced both of the above losses are reduced none of the above A. has its own power factor C. the resistance between the primary and the secondary of a transformer should be A. If there are 1. provide strength to the windings B. D. high reactance C. chrome steel sheets 192. Calculate the total magnetic flux in a 60-cycle transformer in which the induced emf per turn of the winding is equal to 2 V. assumptions do not include Ideal transformer . 190. Residual C.02 mWb C. nickel alloy steel stampings D. The net cross section of a transformer is 20 square inches.182. decrease the reluctance of the magnetic path D. electrically electromagnetically 194.42 mWb 185. high or low depending upon whether it is step up or step down respectively 197. D. The steel for construction of transformer core is made so as to made A. C. C. 7. A. 7. B. reduce eddy current losses 196. What is common in the two windings of a transformer? The principle of working of working of the transformer is 187. voltage A transformer operates A. always at unity power factor B. B. power power factor 188. high permeability and low hysteresis D. low permeability and high hysteresis B. silicon steel sheet C. physically B. high permeability and high hysteresis 193. magnetically The main function of the iron core in a transformer is to A. 186. as high as possible C. B. Eddy D. as low as possible B. D. determine the primary induced emf. C.50 mWb B. 3780 V 3945 V 3590 V 3850 V 183. low reactance B.000 turns in the primary. high conductivity D. Electric power is transformed from one coil to the other in a transformer A. A. low permeability and low hysteresis C. C. B. Magnetizing 184. The maximum flux density is 11 kilogausses. to decrease the hysteresis losses C. The path of the magnetic flux in a transformer has A. Sneak B. D. A. how much current lows through it? A. The laminations are made from A. 10 A 12 A 20 A 15 A static induction dynamic induction mutual induction self-induction used to change the value of A. If the high voltage side has 30 turns. D. Transformer is C. 7. at power factor depending on the power factor of the load 191. kWh D. B. kV C. without changing the power B. A. B. low at low loads and high at high loads B. common core flux C. The concentric windings are used in core type transformer with A.c. D. same at all levels D. E1/E2 B. B. not change C. low voltage winding of small rating transformers C. D. 50% to 70% 60% to 75% 80% to 90% 90% to 98% The resistance of the low voltage winding of a transformer B. frequency or shape 202. air core closed iron core aluminum core open iron core If in a transformer the secondary winding are doubled and at the same time the primary voltage is reduced to half. LT winding placed next to core HT winding placed next to core LT winding on the outer side HT winding on the outer side 207. kW B. maximum flux in core and frequency only frequency. Joule’s law C. the primary induced emf 209. high at low loads and low at high loads C. high voltage winding of large rating transformers D. permeability of the material of the core 199. The induced emf in the transformer secondary will depend upon A. B. kVA 210. the secondary voltage B. Faraday’s law B. be reduced to a quarter . signal A. high voltage winding of small rating transformers B. C. D. C.A. D. leakage flux B. is equal to the resistance of its high voltage side is more than the resistance of its high voltage side is less than the resistance of its high voltage side either B or C 201. C. D. B. without changing power. flux and number of turns in the secondary frequency of the supply only number of turns in the secondary only 203. C. At every instant the direction of secondary current in a transformer must be such as to oppose any change in flux. transformation ratio is A. size of core D. C. be halved B. without changing its frequency D. the drop across resistance and reactances C. 211. none of the above 208. This is in accordance with A. Cross-over windings are used for A. varies at low loads and constant at high loads 206. D. Lenz’s law D. What type of core is used for a high frequency transformer? A. In an ideal transformer on no-load. The magnitude of the mutual flux in a transformer is A. the secondary induced emf D. The efficiency of the transformer is normally in the range of A. D. Transformers are rated in A. C. be four times as much D. The reactance of a transformer is determined by its A. zero reactance of windings zero resistance of windings no leakage flux no saturation of flux 198. the primary applied voltage is balanced by A. then secondary voltage will A. The basic property of the transformer is that is changes the voltage level of an a. 200. N1/N2 The voltage E2/E1 N2/N1 205. without changing its shape C. C. Coulomb’s law 204. much higher D. 7. cooling and lubrication 217. Which is the common method of cooling a power transformer? A.2 + j0. insulation and cooling D. A. Calculate the total magnetic flux in a 60-cycle transformer in which the induced emf per turn of the winding is equal to 2 V. 983 W D.45 ohms.219 ohm D. calculate the resistance of the secondary windings.400-V. The maximum flux density is 11 kilogausses. Calculate the voltage across the secondary . Determine the core loss when the transformer is connected across a 4. The transformer oil used in transformer provide A. respectively. C. If the voltage induced per turn is 8 volts. single-phase transformer has primary and secondary winding impedances of 5.220 ohm 226. 7. sometime same 218. 3590 V 3850 V 221. decreases the weight per kVA B. determine the primary induced emf. 12 to 20% 213. 0. 50-Hz source. always same C. The net cross section of a transformer is 20 square inches. always different B. In transformer the purpose of breather is to A. 7. The no-load current of a transformer in terms of full-load current is usually A.209 ohm B. What is the efficiency of transformer compared with that of electrical motors of the same power? A. Find the current in the common winding.25 Tesla.600-volt. A. to take insulating oil from conservator C. The frequency is 60 Hz. 3780 V B. extract moisture of the air B. D. 1 to 3% B. 20 A 15 A 222.B. A. 10 A B. 3 to 9% C. 977 W C.202 ohm C. much smaller B. B. 362 220.02 mWb D. 50 Hz singlephase distribution transformer is 1. The eddy current and hysteresis losses of a 4. 40 A C. cooling and lubrication B. insulation and lubrication C. how much current flows through it? air cooling air blast cooling oil cooling natural cooling 214. 7. increases the weight per kVA C. 3945 V C.000 turns in the primary. D. The use of higher flux density in transformer design A. decreases the weight per kW 215. 12 A C. A 20-kVA. 0. to provide cooling to the winding D. C. somewhat smaller C. D. increases the weight per kW D. 292 D. In any transformer the voltage per turn in primary and secondary remains A. If the high voltage side has 30 turns. always in the ratio of a D. 2000/400 V. 375 212. The maximum flux density in the core of a 3000/240-V. 50 A D. respectively. A. determine the 2 cross-sectional area of the core in cm . A. respectively. 30 A B. 994 W B. A. to provide insulation to the winding 219.42 mWb 225. A 10-kVA. If there are 1. none of these 224.50 mWb C. 60-Hz singlephase distribution transformer are 280 and 560 watts. 9 to 12% D. 500-V load is to be supplied by an ideal step-up autotransformer from a 400-V source. The low side of a certain welding transformer has 2 turns and delivers 300 A. 0. insulation. 967 W 223. 0. If the primary winding resistance is 20 ohms. The ratio of transformation is 10:1 and the mean length per turn of the primary is 15% greater than that of the secondary.50 mWb B. about the same 216. The current densities in the primary and secondary windings of a step don transformer are 1250 and 1500 A per square inch.0 + j10 and 0. 288 A. 80% power actor lagging. A. 100 amperes D. three-phase transformer consisting of two singlephase transformers is operating with a balanced three-phase load of 50 kVA. 36. 330 amperes C. A transformer will have negative voltage regulation when its load is A.8. The secondary of a transformer is connected wye-grounded. 400 V C. 200 amperes B.97-kV autotransformer is 100 amperes. 3:1 C. 220 amperes D. square of the load current of the laminated core D.000 volts.500 kVA. D. calculate the load in kVA.887 lagging 229. The first transformer has an impedance of 3% and a rating of 1. A. A 1 k generator supplies power to the load through a transformer.500 kVA. square of the flux density 230. square of the thickness B. 1792. Assume a phase sequence of a-bc.250 kVA while the second has an impedance of 3% and a rating of 1. capacitive B. 1453. If the load current is 40 amperes.83 kVA. 2:1 238. short circuit test C.97 kV autotransformer is 200 amperes. 0. 80 B. C. The secondary current of a 20 kV/7.887 lagging C. A. 0. 440-V at a lagging pf of 0. 70 amperes B.53 kVA 236. 0. 33. Determine the minimum ratings of the transformers.terminals at full load. The current that flows through the common winding of a 20kV/7. 34. C. A. 1363. 1227.51 kVA D. A transformer has a core loss of 64 W and a copper loss of 144 W when it is carrying 20% overload current. Calculate the load shared by the second transformer. 0. 0. . A. 5.34 kVA D. 237. A. A.19 kVA C. 34.15 kVA C.993 lagging B. The load at which this transformer will operate at the maximum efficiency is ____ percent. 239.48 kVA. B.11 kVA 15.8 p lagging and a single phase load of 10 kW resistive connected across c-a leg. square of the frequency C. D. 9. 38.383 lagging. 50 amperes 235. open circuit test D. inductive circuit test 232. consisting of two-single phase transformers is operating with balanced three-phase load of 50 kVA.383 lagging. Determine the secondary current. An open delta. The voltage from line to neutral is 132 volts. 10:1 B. 394 V D. 385 V B. 8:1 D. 0.52 kVA 228. 66 C. 20.40 kVA C. A. An open delta bank. EE Board Exam April 1990 Copper loss of a transformer are determined by means of a A. 0. B. polarity test B. D.993 lagging D. 60 amperes C. 120 75 A 100 ohms load has a pf of 0.393 lagging.32 kVA. Which of the following given below is the eddy current loss not proportional to A. Best matching will be produced when transformer ratio is approximately A. D. resistive C.06 kVA B.84 kVA 233. 30.28 kVA B. when the primary is supplied with 2. D. 39.393 lagging. Determine the operating pf of each transformer. 0. Two transformer are connected in parallel supplying a load of 2. 379 V 227. Determine the current that flows through the common winding. A.8. inductive both B and C 231. 35. A.80 kVA. 440 V at 0.64 kVA B. 150 amperes 234.