Sorry to be rude fellow members, but some of your advice IS WRONG AND WILL KILL HIM OR THE OPERATOR. As Bruce has said use a hall effect CT which is the safest option that is commercially available. Any material/ component you use should be designed for this voltage and I don't mean just 900VDC but with at least CAT1 surge rating capability which is 2500V and preferably CAT3 which 6000V, since your load is highly inductive. Preferably go for ready made equipment made by a regular certified manufacturer to measure and isolate the current. Then you can connect it to whatever stuff you want.