Interested in people's thoughts/experience here. I've just been testing out the insulation resistance on a 20 year old surface water pollution control facility. It has a large number of penstocks with Auma actuators.
Here's the puzzle: on a few of them, the resistance - although passable - is conspicuously low at 3-4MR in one case, between phases, but absolutely fine phase to earth. The cables are SWA four core, with CPC and the armour connected to CPC both ends.
I don't see how the insulation resistance can measure 3-15 MR between phases, but several hundred MR or even GR phase-earth in the same cable? Any thoughts? The only thing I can think is if an overcurrent occurred at some point and heated up the phase conductors and left the CPC insulation relatively unscathed? All the actuators are healthy.
The actuators were complete disconnected during the test, of course, so this is purely cable insulation, although there is a plug-type connector on one end that would be onerous to remove.
Interested if people with more experience than me see this all the time or is it odd?
Here's the puzzle: on a few of them, the resistance - although passable - is conspicuously low at 3-4MR in one case, between phases, but absolutely fine phase to earth. The cables are SWA four core, with CPC and the armour connected to CPC both ends.
I don't see how the insulation resistance can measure 3-15 MR between phases, but several hundred MR or even GR phase-earth in the same cable? Any thoughts? The only thing I can think is if an overcurrent occurred at some point and heated up the phase conductors and left the CPC insulation relatively unscathed? All the actuators are healthy.
The actuators were complete disconnected during the test, of course, so this is purely cable insulation, although there is a plug-type connector on one end that would be onerous to remove.
Interested if people with more experience than me see this all the time or is it odd?
