Hey, I have to know are you a professional singer or do it more as a hobby?
4 years, 10-15 concerts every Christmas, state competitions, formals, tuxedos. I tend to have an alto or tenor range. What background do you have?
Wow, that is definitely professional! I only have Songburst competional under my belt. You are so lucky to be able to do what you love. 
5 to 10 hours of training a week for 4 years... and all the trips, practice to be sure. I've heard it said, talent, skill, discipline.... Michael Phelps was an Olympic swimmer, due to his showing up every day for years. Also, singing for hobby, that can be wonderful too. 
How do you train to sing? Do you use a certain song that you sing or have a melody that you use to practice?
Usually, practice starts with a group of 15 or more of us, up to 80 sometimes in the larger groups. I was in the top 20 voices of 1000 students for a few years. Scales are usually the way you start practice, different tones. 
That is incredible, I am so impressed! Singing in unison with a group can transcend people into another place.
It seems like, when you perform regularly, it is the rule of thirds. A third of the performances, would be average, another third would just be awful, and the last third - that would be the transcendence you speak of. 
Some of the feature chorus in America would be lucky to have you, have you ever thought of singing at the super bowl or something like that?
I sing with a few friends, more acoustic these days, for fun. Less pressure. Maybe you enjoy singing by yourself too.