Question

2. The local transformer shown below provides the last voltage stepdown in a power distribution system. A common sight on utility poles in residential areas, it is a single-phase transformer that typically has a 13.8-LV rms line to neutral on its primary coil, and a center tap secondary coil provides both 120 Vrms and 240 Vrms to service several residences. A typical example of this transformer is shown below. Find the tums ratio necessary to produce the 240-V mms secondary voltage. Assuming that the transformer provides 200-A mms service to each of 10 13.8 kV houses, let us determine the minimum power rating for the transformer and the maximum current in the primary. (15 pts) Substation 13.8 kms 120 Vrms 240 Vrms 120 Vrms Local step-down transformer transformer 240/120 V output

Answer 1

Turn ms ratio To 13-8x10? 240 = 0.0174 - Secondary uvrent a = 10 x 200 2000 A Minimum power rating is when output is teken from 120 12o Venus 120x2000 = 240 KVA -> > For morcunum prunery current & neglecting the losses. 4 Vp Ip = Vs Is >> I IPE (mere) 240 x 2000 13.8x16 3 2 34.78A