Problem 81-3    Source:  Problem elaborated by the author of the site.

Be the voltage V_AC = 380 ∠250°. Find the phase voltage V_BN.

Solution of the Problem 81-3

In this case, to find the phase voltage modulus, simply divide the line voltage by root of three (eq. 81-02). Note that there is no correspondence between the letters that make up the first index of the tensions. On the other hand, it is known that V_BN is advanced by 90° in relation to V_CA as can be seen in the Figure 81-03.1 and confirmed Here!

So we can write that:

Note that by inverting the index letters, we must subtract (or add, whichever is more convenient) 180° from the phase of the voltage. It is like V_BN is advanced by 90° in relation to V_CA, besides having a phase voltage equal to 380 / √3 = 220, so we can write V_BN as: