maintenance issues of bus ducts from transformer secondaries to MV switchgears

[gunther]

It is a common problem that bus ducts from power or distribution transformer secondaries connected to medium or low voltage switchgears suffer catastropic failures due flashover cause by water or moisture ingress as well as dust. The common solution that we do to avoid this problem is to open these bus ducts for inspection , maintenance or cleaning which is time consuming and sometimes only disturb the bus insulation integrity which also causes voids and then cause partial discharge. Now my question . Is there a way to monitor these bus ducts to avoid some of these time consuming but also neccessary maintenance issues?

I would surely appreciate some good ideas folks. Thank you.

 

[big john]

Online monitoring can be done with partial-discharge detection; I've seen permanent PD detectors in iso-phase and non-segregated bus duct because the open frame designs make for easy installation.

Offline monitoring, at the bare minimum you need to be doing insulation resistance testing, NETA also lists regular dielectric withstand testing. Obviously doing DC hipots on insulation systems requires a bit of care because it's considered a destructive test, so if you go that route do a ramp or tip-up test.

Since this is MV gear, I might consider doing power-factor testing instead. It is not considered a destructive test, but the problem is because this gear apparently exists in high-humidity environments and the insulation is likely hygroscopic, it makes it difficult to get baselines or do reliable trending. While we might look for results within a few percent, it's not uncommon to see dry-type gear in these environments upwards of 10% PF, even for brand new equipment.