The no-load secondary voltage (V₂, NL) is 250 V.

Step 6: Calculate the secondary voltage at full load
The no-load secondary voltage ($V_{2, \text{NL}}$) is $250 \text{ V}$.
The secondary voltage at full load ($V_{2, \text{FL}}$) is:

$$V_{2, \text{FL}} = V_{2, \text{NL}} - \Delta V_2$$ $$V_{2, \text{FL}} = 250 \text{ V} - 53.89 \text{ V}$$ $$V_{2, \text{FL}} = 196.11 \text{ V}$$

The approximate value of the secondary voltage at full load is $\boxed{196.11 \text{ V}}$.