On the book is written that generally Is and It are equal to 0 during a single-phase fault ground, and I really don't get the reason behind this statement.
The line prior to the fault event is supposed to be symmetric and connected to a load, therefore after the fault I don't get why Is and It should be equal to 0. I would say that Is and It are affected by the fault but not necessary are equal to 0 and their value depends on the characteristic of the load (i.e if the load is grounded or not).
Furthermore, if we suppose that the system is not grounded (So R is very large), how does the fault evolve?
Hope that my questions are clear. Have a good day!