mv cable terminations
mv cable terminations
(OP)
i would like to get opionion on attached photo showing some damage to cable terminations. application vsd, secondary of 12 pulse transformer, 1.7kv, cable is 3.3/6kV grade. installation is 1yr in service
this was noticed as part of routine inspection.
terminations on one winding seem to be ok but other winding seems to be heat damage around earth screens
what are thoughts on leaving this vsd in service with this, there is insulation monitor on DC link with early alarm for low insulation and also trip for too low earth faults.
this was noticed as part of routine inspection.
terminations on one winding seem to be ok but other winding seems to be heat damage around earth screens
what are thoughts on leaving this vsd in service with this, there is insulation monitor on DC link with early alarm for low insulation and also trip for too low earth faults.






RE: mv cable terminations
RE: mv cable terminations
RE: mv cable terminations
RE: mv cable terminations
My first thought was same as Scotty's.
Question: These are single-conductor cables, correct? How many amps is each cable carrying? (Actually that makes 2 questions).
I understand that the cables are only 10m in length, but if I am surprised to see both ends of the shields grounded. I would think that the harmonics might be contributing to the induction of current to the shields. (ie don't forget that each conductor is carrying 6-pulse type of current waveform - very high in harmonics).
I would be hesitant to leave this for too long. Is this part of the circuit within the protection zone of the ground-detection circuit? (sorry, that is Q3).
Your saving grace is the fact that the cable is rated for 6kV, but operated at 1.7kV.
Regards,
GG
"Wish I didn't know now what I didn't know then." -- Bob Seger
RE: mv cable terminations
I was in process of working out derate for bunch, temp and circ current losses. Run is actually more like 20m. Run is not ideal either last 2m either end comes out of three times trefoil arrangements to three x 3 parallel conductors of each phase, so 20% of run is non trefoil.
Was using the guide for cable circ current losses as found in oxonite engineering handbook (as referenced in another thread i found).
So for 6 pulse content should i factor in an additional margin in the circuit load for non-linear waveform, e.g +10% ??
RE: mv cable terminations
Re q1. Yes single core