Utilities Medium Voltage fault detection methods

[Joaopato]

I'm trying to determine how other utilities identify the faulty medium voltage cables after a switchgear trip in a main substation. Assuming that a network is entirely underground, do you measure each segment of the network and a progressive feed oh healthy sections or you do live connection of the switch gear until you find the faulty one?
Can you help?

 

[MAS2000]

We use earth fault passage indicators (EFPI) or fault passage indicators (FPI) on the secondary substations on underground open ring distribution circuits. EFPI or FPI indicate the passage and path of fault current. Based on their indication the faulty cable section between two secondary substations is identified and isolated; restoring supplies to all other healthy cable sections via operation of the ring open points and/or main substation CB.

In some cases where EFPI are not yet installed; then faulty section is identified by energizing the cable section in sequential way starting from main substation. This could result in re-tripping of the restored customers or sometimes healthy customers.

M.A.Sh.
Elect. Engr.