How grounding technique of substation varies with voltage rating?

The grounding technique depends primarily on how the system is earthed, and configuration as well as the voltage. This varies between country, and local practices, but sees below for a general idea.

MV systems like 3.3, 6.6, 11, and 33kV are generally impedance earthed so the earth fault current is limited, which means that the grounding design is relatively straightforward unless it's a small rural substation fed via overhead lines.

HV systems like 66, 132,230, 380kV tend to be solidly grounded so the fault current is much higher, in addition these networks are often meshed, ( multiple sources) so fault current distribution can be quite complex. This means that designing a grounding system has to be done much more carefully as the touch and step voltages can become very high, and in particular the step voltages can exceed the substation boundary fences.