Rishi Kant Sharma ELECTRICAL ENGINEERING DEPARTMENT (EED) Assignment V SUBJECT: ELECTROMECHANICAL ENERGY CONVERSION I SEMESTER:III YEAR: 2nd yearSESSION: 2014-15 SECTION: EE-B SUBJECT CODE:Date of submission: UNIT-5: Three phase Transformers. Q.1:Anidealthreephasestepdowntransformer,connecteddelta/stardeliverspowertoa balancedthreephaseloadof120kVAat0.8powerfactor.Theinputlinevoltageis11kV and the turns ratio of the transformers, phase to phase is 10. Determine the line voltage, line currents, phase voltages and phase currents on both the primary and secondary sides. Q.2:A2400/220V,300kVA,threephasetransformershasacorelossof33kWatrated voltage.Its equivalent resistance is 1.6%.Calculate the transformer efficiency at 0.8 pf at (i) full load (ii) at half load. What is the load at which the transformer efficiency would be maximum? Calculate its value at a pf of 0.8. Use pu method. Q.3: Two transformerseach rated 250 kVA, 11/2kV and 50 Hz are connectedinopen delta on both primary and secondary. (a) Find the load kVA that can be supplied from this transformer connection. (b)Adeltaconnectedthreephaseloadof250kVA,0.8pf,2kVisconnectedtotheLV terminalsofthisopendeltatransformer.Determinethetransformercurrentsonthe11kV side of this connection. Q.4:Explaindifferentmethodsofconnectionswithphasordiagramforconvertingthree phases to six phases. Q.5: Explain three phase to twelve phase conversion methods using phasors diagram. Q.6:A3phase,100kVA,6600/1100Vtransformerisdeltaconnectedontheprimaryand starconnectedonthesecondary.Theprimaryresistanceperphaseis1.8ohmandthe secondary resistance per phase is 0.025 ohm. Determine the efficiency when the secondary is supplying full load at 0.8 p.f. and iron loss is 15 kW.