As mentioned above, one of the major goals of any Electricity Distribution Network Operator is to improve the quality of the energy supply, which is assessed by improving the SAIDI and SAIFI quality indicators.

Improvement of these quality indicators is achieved at comparatively small costs, by reducing the time to track failures in the Medium Voltage (MT) network through the use of Fault Passage Indicators. These devices are installed at appropriate locations on the overhead and underground MV networks and provide local or remote readings in the event of a short circuit current passing through.

Despite the simplicity of the idea, it has proven to be a cost-effective solution in improving the distribution network’s reliability. Many studies have linked the development of Fault Passage Indicators technology with significantly improved SAIDI and SAIFI quality indicators.

In particular:

• Improved SAIDI: Improvement is proportional to the number of Fault Passage Indicators installed and the degree of prior existing network automation.
• Improved SAIFI: By using Fault Passage Indicators, we avoid identifying the fault point trough successive electrification trials in fault conditions, a practice that puts strain on network components (cables, coupling and protection devices, insulators, etc.) resulting in reduced life span and an increase in the number of fault passages (increased SAIFI).

In the event of a fault passage, the reading is provided:

• Locally: For example, if a Fault Passage Indicator is installed on a MV/HV Substation indoors (Substation inside a building), a local light indicator lights up (e.g. on the façade of the building housing the Substation) so that the technical crew may locate the point of failure easily.
• Remotely: New technology Fault Passage Indicators transmit fault detection results through a telecommunications network to the local RDCCs. The use of Fault Passage Indicators with telecommunication leads to an even greater increase in network reliability, by reducing the time needed to locate the point of the fault further.

On the basis of the above, it is concluded that the installation of Fault Passage Indicators, apart from improving the SAIDI and SAIFI quality indicators and ensuring compliance with the relevant regulations set by the Regulatory Authority for Energy (Regulatory Decision), can also give rise to considerable financial benefits, i.e. a decrease in the cost of Undistributed Energy and a decrease in the level of investments required for network improvement as mentioned with regard to MV/HV Substation Control Units (MV underground Substation  network).