Hey Gentleman!
Hi
For example , suppose that the frequency of switch is about 120KHZ , if your switch become on -off , the current of transformer will be triangle wave(approx) and the voltage across it will be square wave . ok? so , you can use a function generator to make this square wave with 120KHZ frequency for testing the behavior of your transformer . is your transformer multi secondary? **************(it is important to know for me to answer about phase)
And at first step you don't need to use DC voltage for testing your transformer.
And about ratio of change: consider that you designed transformer with 1.2 ratio of change ( if you give to it a 120KHZ 100 volt , it will give to you a 120KHZ 50volt as well as) with the oscilloscope and function generator, try to know that , is the real behavior of transformer like your calculations?
Best Wishes
Goldsmith