In per-unit sequence models of three-phase three-winding transformers, for the general zero-sequence network, the connection between terminals \(\mathrm{H}\) and \(\mathrm{H}^{\prime}\) depends on how the high-voltage windings are connected:

(i) For solidly grounded Y, ____________ \(\mathrm{H}\) to \(\mathrm{H}^{\prime}\).

(ii) For grounded \(\mathrm{Y}\) through \(Z_{n}\) connect ____________ from \(\mathrm{H}\) to \(\mathrm{H}^{\prime}\).

(iii) For ungrounded \(\mathrm{Y}\), leave \(\mathrm{H}-\mathrm{H}^{\prime}\) ____________.

(iv) For \(\Delta\), ____________ \(\mathrm{H}^{\prime}\) to the reference bus.