The purpose of the continuous on line diagnostics is to highlight incipient problems before these can cause power system outage with the goal of better handling maintenance intervention. In order to achieve this goal it is necessary to set up a continuous monitoring system: any further off line tests with dedicated test equipment can be programmed depending on the actual apparatus conditions.
ISA has developed EDS – Expert Diagnostic System for the continuous monitoring of substation devices.

EDS units are designed to continuously monitor the condition of:
• High Voltage and Medium Voltage Circuit Breakers
• Current and Voltage Transformers
• High Voltage Surge Arrestors (MOV’s)
The EDS is easy to install and, once configured, operates continuously. EDS units are designed to operate reliably under extreme weather conditions and electrical interference found in normal substation operations. In particular:
• Modules mounted outdoor are IP 65 and designed to work over an extended temperature range (from - 40°C to + 85°C).
• Self-diagnostics continuously tracks the condition of the EDS and issues alerts if an abnormality is detected in the system.
• By the continuous monitoring of the key parameters, EDS detects malfunctions in early stage and issues prioritized alarms communicating abnormal conditions and guiding maintenance decisions.