Upon receiving an alarm for low oil pressure on an underground transmission cable, what is the first step to protect the line?

To protect an underground transmission cable following an alarm for low oil pressure, the appropriate first step is to isolate the line. The reasoning behind this is that low oil pressure can indicate a significant issue, such as a leak or failure in the cable's insulation system. This can pose risks not only to the integrity of the transmission line itself but also to the safety of the surrounding environment and equipment.

By isolating the line, operators can prevent further damage from occurring while they assess the situation. This action ensures that the electrical system remains stable, avoiding potential faults that could arise from operating under compromised conditions. Once the line is isolated, further actions can be taken, such as monitoring the pressure or addressing the oil supply, but isolation is the immediate priority to safeguard the infrastructure and personnel.

Monitoring the pressure or resetting the alarm would not address the immediate issue posed by low oil pressure and could lead to exacerbation of any underlying problems. Increasing the oil supply may be necessary later, but only after confirming that it is appropriate and safe to do so.