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TABLE 1:   Voltage and Current Ratings of Transformers
Transformer Losses and Efficiency - h1011v4_56

Electrical Science Volume 4 of 4
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Transformers TRANSFORMER THEORY D-Y:   primary phase current = I 3 10.4 1.73 6  amps Example 3: Find  the  secondary  line  current  and  phase  current  for  each  type  of  transformer connection, if primary line current is 20 amps, and the turns ratio is 4:1. D-D:     secondary line current   = 4(20) = 80 amps secondary phase current = aI 3 4  (20) 1.73 46.2  amps Y-Y:    second line current = aI = 4(20) = 80 amps second phase current = aI = 4(20) = 80 amps Y-D:    secondary line current = aI = (1.73)(4)(20) = 138.4 amps 3 secondary phase current = aI = 4(20) = 80 amps D-Y:    secondary line current = aI 3 4  (20) 1.73 46.2  amps secondary phase current = aI 3 4  (20) 1.73 46.2  amps Transformer Losses and Efficiency All  transformers  have  copper  and  core  losses.   Copper  loss  is  power  lost  in  the  primary  and secondary 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  Loss I2P  RP I2S  RS where IP    =    primary current IS    =    secondary current RP  =    primary winding resistance RS  =    secondary winding resistance Rev. 0 Page 11 ES-13







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