Three single-phase transformer are connected as a transformer bank rated at 18MVA, 13.8kV(delta)/120kV(Y) // one side of the transformer bank is connected to a 120 kV transmission line and the other side is connected to a three-phase load of 12MVA at 0.8 lagging power factor compute the following

  1. I'm keep confusing with what value is for 13.8kv(delta)/120kv(Y), for (Y) sometimes its V_phase and sometimes its V_line-to-line.. How do you decide this

  2. Is turn ratio N1/N2 = VAB(delta) / Vphase(wye) ??

  • \$\begingroup\$ Not sure I understand your question. What don't you understand? Do you understand why the delta and Y ratings are different? \$\endgroup\$
    – Michael
    Commented Dec 20, 2013 at 5:53

1 Answer 1


"Is the equipment rating in line-neutral volts or line-line volts?"

Nominal voltages for three-phase equipment are always specified as line-to-line voltage, regardless of if the equipment is intended for connection in delta or wye.

In your case, the transformer is 13,800V line-to-line LV, and 120,000V line-to-line HV.

Occasionally, both the line-to-line and the line-to-neutral voltage are specified; as in a three-core cable labelled "11/6.6kV", with 11kV worth of insulation between phases, and 6.6kV of insulation between each phase and ground.

What is the turns ratio across a delta-wye transformer?

In a three-phase Dy transformer with voltage ratio 1:1, the delta winding will have \$ \sqrt{3} \$ more turns than the wye winding.

  • \$\begingroup\$ NOTE in aerospace they cite the phase voltage as oppose to line-line voltage: 115V 3ph 400Hz as oppose to ..200V \$\endgroup\$
    – user16222
    Commented Dec 20, 2013 at 11:14

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