I suggest to distinguish two points:
- the operation of the circuit in the link
- is there any way to perform TDR measurements on a powered 10 kV cable
The circuit generates short rectangular pulses of a few volts, as shown in the waveform diagrams. There's no way to operate this simple circuit on a powered AC line.
It's most likely possible to make TDR measurements on a powered HV AC cable. Besides a suitable signal coupler, you'll need a sufficient high signal voltage that can be detected over the AC voltage and respective noise level. Instead of a simple rectangular pulse, the measurement would use a complex signal that's optimized both to the limited cable bandwidth and expectable noise spectrum.