Transformer +/- 30 Degree

[EEVA PE]

In a Delta - WYE or WYE - Delta Transformer does the High to Low or Low to High factor in when determining whether to add or subtract 30 degrees. Below is how I see things. I am not sure if I should be factoring in whether a transformer is going from low to high or high to low when determining to add or subtract 30 degrees. Is my understanding below wrong or right?

High Side Delta to Low Side WYE - one subtracts 30 degrees

Low Side Delta to High Side WYE - one adds 30 degrees

High Side WYE to Low Side Delta - one subtracts 30 degrees

Low Side WYE to High Side Delta - one adds 30 degrees

 

[Flyer_PE]

^I've always dealt with the conversion graphically. The rules of whether you are adding or subtracting 30 degrees only hold true for standard connections. I've done a lot of work on non-standard systems. As a result, I always draw out a little phasing diagram and solve it that way.