ScottyUK
Electrical
- May 21, 2003
- 12,915
I've just had a fun-packed evening investigating a fault on a generator excitation transformer. In the course of the investigation we removed the HV (15.5kV) cable box cover and found a real mess.
The HV supply from the generator terminals is via 3x single-core aluminium, XLPE insulated, wire screen, aluminium armoured, PVC sheathed cable.
The lugged connection onto each of the three porcelain phase bushings of the transformer had been wrapped in a self-amalgamating rubber tape over the metal parts. The reason for the tape wrapping, and those who authorised its use, is not known at present.
There appears to have been a chemical reaction taking place within the cable box which has evolved some highly corrosive vapour or gas which has attacked the steel cable box interior, the brass glands, and the copper earthing bar. The steel in locations where the liquid had breached the paint coating was in a severely corroded state. There was also a significant volume of liquid - I am reluctant to say water - over all internal surfaces of the cable box and the cables, yet all gaskets and gland washers appear intact. It is almost as though the liquid appeared within the box and condensed on every internal surface. We treated the liquid as a chemical release, took samples, then flushed the whole lot with water into the bund before investigating further.
The rubber tape - which normally becomes a homogeneous hard rubbery mass over time - has deteriorated into something with the consistency of chewing gum. The Raychem heatshrink termination - which had been made off correctly so far as can be determined - shows signs of major PD activity with large-scale treeing visible and some surface burning and material loss also being evident in the area where the overlap to the rubber tape occurred.
Has anyone seen anything like this before? Also, can anyone suggest what the liquid might be? I think it is likely to be some sort of acid - sulphuric or nitric - although I can't account for its presence unless it is a byproduct of the chemical breakdown. I believe the rubber tape is a natural rubber (latex) based material which is (was?) presumably vulcanised, hence my suspicion of sulphuric acid. Any other comments about any part of what I have described are very welcome too.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
The HV supply from the generator terminals is via 3x single-core aluminium, XLPE insulated, wire screen, aluminium armoured, PVC sheathed cable.
The lugged connection onto each of the three porcelain phase bushings of the transformer had been wrapped in a self-amalgamating rubber tape over the metal parts. The reason for the tape wrapping, and those who authorised its use, is not known at present.
There appears to have been a chemical reaction taking place within the cable box which has evolved some highly corrosive vapour or gas which has attacked the steel cable box interior, the brass glands, and the copper earthing bar. The steel in locations where the liquid had breached the paint coating was in a severely corroded state. There was also a significant volume of liquid - I am reluctant to say water - over all internal surfaces of the cable box and the cables, yet all gaskets and gland washers appear intact. It is almost as though the liquid appeared within the box and condensed on every internal surface. We treated the liquid as a chemical release, took samples, then flushed the whole lot with water into the bund before investigating further.
The rubber tape - which normally becomes a homogeneous hard rubbery mass over time - has deteriorated into something with the consistency of chewing gum. The Raychem heatshrink termination - which had been made off correctly so far as can be determined - shows signs of major PD activity with large-scale treeing visible and some surface burning and material loss also being evident in the area where the overlap to the rubber tape occurred.
Has anyone seen anything like this before? Also, can anyone suggest what the liquid might be? I think it is likely to be some sort of acid - sulphuric or nitric - although I can't account for its presence unless it is a byproduct of the chemical breakdown. I believe the rubber tape is a natural rubber (latex) based material which is (was?) presumably vulcanised, hence my suspicion of sulphuric acid. Any other comments about any part of what I have described are very welcome too.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!