Question

A single-phase three-winding transformer has the following parameters${\mathit{Z}}_{\mathbf{1}}\mathbf{=}{\mathit{Z}}_{\mathbf{2}}\mathbf{=}{\mathit{Z}}_{\mathbf{3}}\mathbf{=}\mathbf{0}\mathbf{+}\mathit{j}\mathbf{0}\mathbf{.}\mathbf{05}\mathbf{,}{\mathit{G}}_{\mathbf{c}}\mathbf{=}\mathbf{0}$: and${\mathit{B}}_{\mathbf{M}}\mathbf{=}\mathbf{0}\mathbf{.}\mathbf{2}$ per unit. Three identical transformers, as described, are connected with their primaries in $\mathit{Y}$(solidly grounded neutral) and with their secondaries and tertiaries in$\mathit{\Delta }$ . Draw the per-unit sequence networks of this transformer bank.

Short answer

Therefore, the per unit diagram of the system is shown below,

Step-by-step solution

Determine the positive sequence network with the conductance. 

Since single phase three winding transformer’s primary winding is connected in$\mathit{Y}$and secondary in $\mathit{\Delta }$. So, there will be phase shift of for the single phase.

The conductance of the winding is zero and impedance is same. The per unit positive sequence network is given by,

Determine the final sequence after removing the conductance and susceptance.

Since the$G_c$and $B_M$are connected in the parallel and$G_c=0$. So, the parallel combination of this two also becomes equal to zero.

The positive and negative sequence would be the same and shown below.