30kv ? it is pretty familiar for me ! i think it is for another thing ! anywhere . why that way to achieve 0-30kv ? why not an SMPS ? it will be pretty simpler . and a notation , be careful , when you want work with this voltage . and remember , at least one millimeter instead of each kv ! at low frequencies and DC ! anywhere , if you need bilateral circuit to measure , you won't need to measure both cycles . because both are the same ! hence , you can use two dividers and then rectify it , and then a linear opto coupler such as IL300 . . don't forget that resistors should be for this voltage and with high value such as 100Mohms , or 1Gohms .
Best Wishes
Goldsmith