Question

The leakage reactance of a three-phase, $\mathbf{300}\mathbf{}\mathbf{MVA}\mathbf{,}\mathbf{}\mathbf{230}\mathbf{Y}\mathbf{/}\mathbf{23}\mathbf{∆}\mathbf{kV}$transformer is 0.06 per unit based on its own ratings. The Y winding has a solidly grounded neutral. Draw the per-unit equivalent circuit. Neglect the exciting admittance and assume the American Standard phase shift.

Short answer

The zero, positive and negative sequence diagrams are drawn below:

Step-by-step solution

Determine the phase shift between star and delta connection of transformer.

It is given that, the primary side of transformer has star connection with solidly grounded neutral and secondary has delta connection.

There will be a $\mathbf{30}\mathbf{°}$ phase shift between star and delta connection.

Determine the per-unit equivalent circuit.

The zero sequence, positive sequence and negative sequence per-unit equivalent circuit is drawn below:

In the diagram, the transformer leakage reactance $0.06\mathrm{pu}$is shown.

Also, the phase shift is mentioned.

In zero sequence diagram. As the star connection is solidly grounded, it will be closed and delta will be open.

The positive and negative sequence diagram will be same.