High Voltage Cable Nitrogen Purging
Nitrogen purging is a system that can be applied to cables that have had ingress of moisture and or water into the conductors and or screens of a high voltage XLPE insulated cable. The dry and very pure nitrogen forces all the moisture from the conductors and the screens of high voltage cables over a period of time which will increase the IR values of the XLPE insulation and deliver a longer lasting installation.
Problems with ingress of moisture into cables.
- Water treeing in the primary insulation in a cable with ingress of moisture
- Electrical treeing of the primary insulation causing failure
- Shortened life expectance of the high voltage cable.
Results after Nitrogen purging
- Vast improvement in IR tests
- Flat lining on Tan Delta tests on the insulation.
How we achieve this
Firstly we engineer the injection method for your requirements, Cable size, cable application, and general spec of the installed cable as some cable joints will have to be dis-assembled and also some terminations will have to be re-worked prior to purging of the cables.
We would firstly complete a Tan Delta test on the installation together with an IR test to give us a true indication of the state of the insulation this is then used as the datum point, prior to purging of the high voltage cables.
The Nitrogen machine we had engineered manufactures 30 cubic meters an hour of 99% pure nitrogen at between -70 to -85 Degree dew point at 30 bar, we then reduce the pressure through a low pressure manifold with 9 outlets enabling us to purge the cables at the required and engineered pressure for the cable installation in regard to head pressure of any moisture in the conductors and screens.
Once the nitrogen purging has started we take a relative humidity reading of the gases coming from the remote end of the conductors and screens.
Depending on the moisture content of the conductors and screens I may take up to 4 days with the machine running 24 hours a day to fully dry the conductors and screens and this is taken on a job by job basis.
After we prove with the RH meter that relative Humidity has been reached, we complete an IR test to give us first results of the improvement. We then re-build any joints and terminations and complete a new Tan Delta test and IR test to the installation giving electrical testing proof, of the purging process.
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