Online vs Offline Testing

There is a world of difference between offline monitoring (the annual testing of a cable circuit while it is out of service) and online monitoring (continuous monitoring while the cable is in normal use).

Offline monitoring is like a security camera that takes a picture once a year, while the online method involves constant surveillance. Partial discharge activity often varies in time for example because of loads and season and/or climate changes.
Some types of cables are "self-healing" due to migrating oil inside while others can develop crucial partial discharge activities within several days.
One measurement per year will not give the required accurate information on the cable condition. Using offline testing to locate the cables that are doubtful or weak and then applying KEMA Smart Cable Guard® on those cables to monitor those doubtful or weak cables for a longer time is a logical step of combining offline and online testing.

Online vs offline testing:
Online                                             
No switching (safe)         
No power supply interruption, no rerouting   
No generator needed          
Testing under normal operating conditions   
Cable under normal load monitored     
Continuous monitoring         
Easy installation             
Cost reduction  
         
Offline
Switching (not safe)
Power supply interruption, rerouting
Generator needed
Testing under special test conditions
Cable not under load when tested
Snapshot measurement
Specialist needed for installation
Costly