Question

A single-phase three-winding transformer has the following parameters : Z₁ = Z₂ = Z₃ = 0 + j0.05, G_c = 0 and B_m = 0.2 per unit. Three identical transformers, as described, are connected with their primaries in Y (solidly grounded neutral) and with their secondaries and tertiaries in $\mathbf{∆}$. Draw the per-unit sequence networks of this transformer bank.

Short answer

The zero-sequence diagram of the system is as follows,

The positive-sequence diagram of the system is as follows,

The negative-sequence diagram of the system is as follows,

Step-by-step solution

 Write the given data from the question.

Write the impedance as follows:

Z₁ = Z₂

Z₁ = Z₃

Z₁ = j0.05 pu

The conductance is G_c = 0.

The susceptance is B_m = 0.2pu.

Draw the zero, positive and negative sequence diagram of the single phase three winding transformer.

Consider V_X, V_H and V_M are the primary, secondary and tertiary winding voltage respectively. Assume I_X, I_H and I_M are the primary, secondary and tertiary winding currents respectively.

The zero-sequence diagram of the system is obtained as follows :

The positive-sequence diagram of the system is obtained as follows :

The negative-sequence diagram of the system is obtained as follows :