With reference to three$-$phase, insulated neutral marine electrical distribution systems:

$($a$)$ explain the meaning of insulated neutral;

$($b$)$ state the advantage of this system compared to an earthed neutral system;

$($c$)$ sketch a labelled circuit diagram of ONE arrangement for detecting phase to earth faults;

$($d$)$ describe the indication from the arrangement sketched in Q$8($c$)$ for EACH of the following conditions:

no earth fault;

a phase to earth fault.

$($e$)$ explain the voltage stress experienced by the insulation of the two healthy phases while there is an earth fault on the other phase.