The transformer has a primary coil with 480 turns and decreases the voltage from U1 = 880V to U = 220V. To determine the transformation ratio and the number of turns in the secondary coil when the transformer is unloaded, we can use the formula:

K = N2/N1 = U1/U2 = N1/(N1+N2)

Substituting the values given in the problem:

K = 480/(480+N2) = 880/220 = 4

Solving for N2, we get:

N2 = 480

Therefore, the transformation ratio is 4 and the number of turns in the secondary coil is 480 when the transformer is unloaded.