The paper use a new dielectric frequency response method to measure the cable insulation’s complex dielectric spectrum at wide frequency domain. During the experiment, Cross-linked polyolefin insulated cables are accelerate aged under thermal and irradiation environment, and measured with elongation at break, Fourier transform infrared spectrum, oxidation induced temperature, and dielectric spectrum as well, to study the property degradation rule. The result indicate that the thermal ageing mechanism is similar to irradiation ageing, of which is the degradation due to polymer molecular chain unlinking, oxidizing material increase and additives content reduce. This chemical constituent changing in insulation could not result traditional electric property change but could be monitored by dielectric loss spectrum curve among wide frequency domain, which stayed stable but shifted to lower frequency as cable degradation. Finally, the paper discussed the main mechanism of cross-linked polyolefin dielectric property changing while ageing according to the electrophysical characteristic of solid insulation, and provided some suggestions about the non-destructive techniques for nuclear power plant cables using dielectric spectrum.

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