Energization angle of a transformer
The term 'energisation angle' is not familiar, but a guess of what it could mean tallies with affecting the inrush current of a transformer, so here goes.

Most transformers are designed so that their steady state B field almost reaches, and does not exceed, the saturation B field for their core material.

If you turn a transformer on when the voltage is at its peak, voltage = k.cos(0), then the field waveform will settle straight into the steady state of equal positive and negative field peaks. This is because the first quadrant of voltage slews the field to its peak. The next half cycle takes it back to zero, and then to the other peak.

If you turn a transformer on when the voltage is zero, voltage = k.cos(pi/2), then the voltage stays the same polarity for a whole half cycle, and tries to take the field to twice the peak of the previous paragraph. If this field is higher than the saturation field, the inductance will collapse, and the transformer will draw a very large current to try to generate the field. The high current produces a voltage drop in the winding resistance, which works to shift the flux back to the steady state range.

The inrush current will vary depending on the angle of switch-on.