Transformers TRANSFORMER THEORYD-Y: primary phase current =I310.41.736 ampsExample 3: Find the secondary line current and phase current for each type of transformerconnection, if primary line current is 20 amps, and the turns ratio is 4:1.D-D: secondary line current = 4(20) = 80 ampssecondary phase current =aI34 (20)1.7346.2 ampsY-Y: second line current = aI = 4(20) = 80 ampssecond phase current = aI = 4(20) = 80 ampsY-D: secondary line current = aI = (1.73)(4)(20) = 138.4 amps3secondary phase current = aI = 4(20) = 80 ampsD-Y: secondary line current =aI34 (20)1.7346.2 ampssecondary phase current =aI34 (20)1.7346.2 ampsTransformerLossesandEfficiencyAll transformers have copper and core losses. Copper loss is power lost in the primary andsecondary windings of a transformer due to the ohmic resistance of the windings. Copper loss,in watts, can be found using Equation (13-7).(13-7)Copper LossI2P RPI2SRSwhereIP = primary currentIS = secondary currentRP = primary winding resistanceRS = secondary winding resistanceRev. 0 Page 11 ES-13
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