Application of polyethylene sheath and swelling powder against water treeing

It is feasible to calculate the water permeation into a cable with a plastic jacket and a swelling tape underneath. The combination of a PVC jacket and swelling tape hardly gives any relief. However, MDPE jackets are certainly promising. If cables are operated with a low load the jackets are approximately isothermal. In that case, they can be adequately protected against water by means of a combination of a jacket with low water permeability and a water absorber within the jacket, e.g. swelling tape. At high load, the temperature gradient makes the water intrusion faster, but the humidity remains lower. Therefore, possibly the critical relative humidity level of 70-75% within the jacket will not be reached.