Question

1. Three single-phase step-up transformers rated at 75 MVA, 13.2 kV/80 kV are connected in delta- wye on a 13.2 kV transmission line. If they feed a 180 MVA load, calculate the following: a. The secondary line voltage b. The currents in the primary and secondary windings C. The incoming and outgoing transmission line currents

Answer 1

a) Secondary phase voltage is 80 kv.

As it is y connected, line voltage Vline = √3Vph

= √3×80 =138.564Kv

b) Secondary phase current

I2 ph = 180 × 10^ 6/ ( √3× Vline)

= 180×10^6/(√3× 80×10^3)

= 1299.038 A

Primary phase current I_{​​​​​​1ph}= 180×10^6/(√3×V1 line)

I_{​​​​​​1ph} = 180×10^6/(√3× 13.2× 10^3)

= 7872.958 A.

C) incoming current I_{​​​​​​1 line} = √3× I1ph = √3×7872.958

= 13636.363 A.

Outgoing line current =secondary phase current = 1299.03A