tutorial singlephase transformer

Rishi Kant Sharma ELECTRICAL ENGINEERING DEPARTMENT (EED) TUTORIAL-4 SUBJECT: ELECTROMECHANICAL ENERGY CONVERSION –I SEMESTER: III YEAR: 2 nd year SESSION: 2014-15 SECTION: EE- SUBJECT CODE: UNIT-4: Single phase transformers Q.1: (a) A 2200/220 V, 50 Hz, 1 phase transformer has exciting current of 0.6 A and a core loss of 361 watts, when its h.v. side is energized at rated voltage. Calculate the two components of the exciting current. (b) If the transformer of part (a), supplies a load current of 60 A at 0.8 pf lag on its l.v. side, calculate the primary current and its power factor. Q.2: A 10 kVA, 2500/250 V, single phase transformer has resistances and leakage reactances as follows: r1= 4.8 ohm, r2= 0.048 ohm, x1= 11.2 ohm and x2= 0.112 ohm. With primary voltage held constant at 2500 V, calculate the secondary terminal voltage, when (a) the l.v. winding is connected to a load impedance of 5+j3.5 ohm. (b) The transformer delivers its rated current at 0.8 pf lagging on the l.v. side. Q.3: The open circuit and short circuit test on a 10 kVA, 500/250 V, 50 Hz, single phase transformer gave the following results, Open circuit test: 500 V, 2A, 100 W (L.V. side) Short circuit test: 25 V, 20 A, 90 W (H.V. Side), Determine: (a) Components of no load current. (b) Approximate equivalent circuit referred to the primary. (c) Efficiency at full load and 0.8 pf lagging. Q.4: A 400/100 V, 10 KVA, 2 winding transformer is to be employed as an auto transformer to supply a 400 V circuit from 500 V source. When tested as a 2 winding transformer at rated load of 0.85 p.f. lagging, its efficiency is 97%. Determine its KVA rating and efficiency as an auto transformer. Q.5: Two single phase transformers of rating 10 kVA, 230/400 V and 10 kVA, 230/410 V are employed for back to back test. The l.v. side is fed from 230 V supply mains whereas a voltage regulator connected to the same 230 V mains feed 25 A in the series connected h.v. windings. For a core loss of 200 W in each transformer, calculate the reading of wattmeter connected on l.v. side. Each transformer has its reactance equal to three times its resistance. Q.6: A 10 kVA, 2500/250 V, single phase 2 winding transformers is used as an auto transformer to raise the supply voltage of 2500 V to an output voltage of 2625 V. the low voltage winding of the 2 winding transformer consists of two equal parts of 125 V each. If both parts of the low voltage winding are used, determine autotransformer kVA output. Also calculate kVA transformed and KVA conducted. Q.7: Two single phase transformers rated 1000 kVA and 500 kVA have per unit leakage impedance of (0.02 +j0.06) and (0.025+j0.08) respectively. What is the largest kVA load that can be delivered by parallel combination of these two transformers without overloading any one? Q.8: A 2000/1000/500 V, single phase transformer three winding transformer is to be used as an auto transformer, with supply voltage of 3000 V. two loads, one of 1050 kVA at 3500 V and the other of 180 kVA at 1000V, are to be energized from this auto transformer output. Draw a suitable diagram of connections and find the currents in various parts of the circuit. Assume loads to have the same power factor.

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Tutorial for practicing numerical questions on single phase transformer subject: EMEC-I

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Rishi Kant Sharma ELECTRICAL ENGINEERING DEPARTMENT (EED) TUTORIAL-4 SUBJECT: ELECTROMECHANICAL ENERGY CONVERSION I SEMESTER:III YEAR: 2nd yearSESSION: 2014-15 SECTION: EE-SUBJECT CODE: UNIT-4:Single phase transformers Q.1: (a) A 2200/220 V, 50 Hz, 1 phase transformer has exciting current of 0.6 A and a core lossof361watts,whenitsh.v.sideisenergizedatratedvoltage.Calculatethetwo components of the exciting current. (b)If the transformer of part (a), supplies a load current of 60 A at 0.8 pf lag on its l.v. side, calculate the primary current and its power factor. Q.2:A 10 kVA, 2500/250 V, single phase transformer has resistances and leakage reactances asfollows:r1=4.8ohm,r2=0.048ohm,x1=11.2ohmandx2=0.112ohm.Withprimary voltageheldconstantat2500V,calculatethesecondaryterminalvoltage,when(a)thel.v. windingisconnectedtoaloadimpedanceof5+j3.5ohm.(b)Thetransformerdeliversits rated current at 0.8 pf lagging on the l.v. side. Q.3:Theopencircuitandshortcircuittestona10kVA,500/250V,50Hz,singlephasetransformer gave the following results,Open circuit test: 500 V, 2A, 100 W (L.V. side)Short circuit test: 25 V,20 A, 90 W (H.V. Side),Determine:(a)Componentsofnoloadcurrent.(b)Approximateequivalentcircuit referred to the primary. (c) Efficiency at full load and 0.8 pf lagging. Q.4: A 400/100 V, 10 KVA, 2 winding transformer is to be employed as an auto transformer to supply a 400 V circuit from 500 V source. When tested as a 2 winding transformer at rated load of 0.85 p.f. lagging, its efficiency is 97%. Determine its KVA rating and efficiency as an auto transformer. Q.5: Two single phase transformers of rating 10 kVA, 230/400 V and 10 kVA, 230/410 V are employedforbacktobacktest.Thel.v.sideisfedfrom230Vsupplymainswhereasa voltage regulator connected to the same 230 V mains feed 25 A in the series connected h.v. windings.Foracorelossof200Wineachtransformer,calculatethereadingofwattmeter connected on l.v. side. Each transformer has its reactance equal to three times its resistance. Q.6:A10kVA,2500/250V,singlephase2windingtransformersisusedasanauto transformertoraisethesupplyvoltageof2500Vtoanoutputvoltageof2625V.thelow voltagewindingofthe2windingtransformerconsistsoftwoequalpartsof125Veach.If both parts of the low voltage winding are used, determine autotransformer kVA output. Also calculate kVA transformed and KVA conducted. Q.7:Twosinglephasetransformersrated1000kVAand500kVAhaveperunitleakage impedance of (0.02 +j0.06) and (0.025+j0.08) respectively. What is the largest kVA load that can be delivered by parallel combination of these two transformers without overloading any one? Q.8: A 2000/1000/500 V, single phase transformer three winding transformer is to be used as an auto transformer, with supply voltage of 3000 V. two loads, one of 1050 kVA at 3500 V andtheotherof180kVAat1000V,aretobeenergizedfromthisautotransformeroutput. Drawasuitablediagramofconnectionsandfindthecurrentsinvariouspartsofthecircuit. Assume loads to have the same power factor. Rishi Kant Sharma Q.9:Asingle-phasepowersystemisshowninFigureP2-1.Thepowersourcefeedsa100-kVA 14/2.4-kV transformer through a feeder impedance of 40.0 + j150 . The transformers equivalent series impedance referred to its low-voltage side is 0.12 + j0.5 . The load on the transformer is 90 kW at 0.80 PF lagging and 2300 V. (a) What is the voltage at the power source of the system?(b) What is the voltage regulation of the transformer?(c)How efficient is the overall power system? Q.10: The maximum efficiency of a single phase 250 kVA, 2000/250 V transformer occurs at 80% of full load and is equal to 97.5% at 0.8 p.f. Determine the efficiency and regulation on full load at 0.8 p.f. lagging if the impedance of the transformer is 9%. References: 1. P.S.Bhimbra, Electrical Machinery, Khanna publication India. 2.I.J.Nagrath&D.P.Kothari,ElectricalMachines,TMHoutlineseries,TataMcGraw Hill.

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