Calculate the primary phase voltage (3.3.1)

Given:
Primary line voltage $V_{L1} = 6.6 \text{ kV} = 6600 \text{ V}$
The transformer is delta-star connected, meaning the primary side is delta-connected.
For a delta connection, the line voltage is equal to the phase voltage.

The primary phase voltage is $\boxed{6600 \text{ V}}$.

Given:
Primary phase voltage $V_{ph1} = 6600 \text{ V}$
Secondary phase voltage $V_{ph2} = 240 \text{ V}$
The transformer ratio ($a$) is the ratio of primary phase voltage to secondary phase voltage:

The transformer ratio is $\boxed{27.5}$.

Given:
Secondary phase voltage $V_{ph2} = 240 \text{ V}$
The transformer is delta-star connected, meaning the secondary side is star-connected.
For a star connection, the line voltage is $\sqrt{3}$ times the phase voltage:

The secondary line voltage is $\boxed{415.68 \text{ V}}$.

The rating of a transformer is typically expressed in kVA (kilovolt-amperes). To calculate the rating, the current (either line or phase) on either the primary or secondary side is required. Since no current information is provided in the question, the transformer rating cannot be determined.