I found this paper which may be of help. It does not answer your question directly but it could give you some pointers as to how to solve the problem.

Article High-Voltage Testing Fundamentals: A Cable Testing Perspective

As regards the safety aspects with the foreseen arrangement, in my mind you should at first consider that in case of a dielectric breakdown, the electrostatic energy of the cable is suddenly released, may be, with a power arc in air. More over a breakdown of the longitudinal insulation of the series inductance implies the application of the test voltge at the 11kV side of the transformer (and associated measurement devices, if any) with a transfer of voltage to the LV side also.