Consider the per-unit sequence networks of \(\mathrm{Y}-\mathrm{Y}, \mathrm{Y}-\Delta\), and \(\Delta-\Delta\) transformers with neutral impedances of \(Z_{N}\) on the high-voltage Y-side and \(Z_{n}\) on the low-voltage Y-side. Answer the following:

(i) Zero-sequence currents (a) can or (b) cannot flow in the \(\mathrm{Y}\) winding with a neutral connection; corresponding zero-sequence currents (a) do or (b) do not flow within the delta winding; however zerosequence current (a) does or (b) does not enter or leave the \(\Delta\) winding. In a zero-sequence network, (a) 1, (b) 2, or (c) 3 times the neutral impedance comes into play in series.

(ii) In \(\mathrm{Y}(\mathrm{HV})-\Delta(\mathrm{LV})\) transformers, if a phase shift is included as per the American-standard notation, the ratio ____________ is used in positive-sequence network, and ____________ the ratio ____________ is used in the negative-sequence network.

(iii) The base voltages depend on the winding connections; the per-unit impedances

(a) do or (b) do not depend on the winding connections.