The surface mine where you work receives its power from a 138 KV utility line that is stepped down to 25 KV for pit distribution. Substations make further reductions to 4,160 volts for operation of smaller equipment such as drills. The pit electrical distribution system has worked well. Then a problem develops.
Power leaving a portable substation goes through two boxes to a drill.
The flag was reset and the system held for about a week. Then the ground monitor trips box B. Within a few days box A trips two more times. As a mine electrician you must find and correct the electrical problem so that production and safety can be maintained.