Development of scientific and technical means of non-destructive diagnostics of domestic superhigh-voltage cables of world level to improve their operational reliability and service life

Application of cables with nano-hardened cross-linked polyethylene (XLPE) insulation is a strategic way to improve the reliability and ecological compatibility of systems of power supplies in all countries. However, there is no normative base for the diagnosis of these cables in Ukraine. Besides there is no necessary diagnostic equipment, despite the fact that the plant "Pivdenkabel" (Kharkiv, Ukraine), the first in the CIS mastered their industrial production for voltages up to 330 kV.

Experiments performed at the plant "Pivdenkabel" have demonstrated that test with direct voltage (2–5 times greater than operational voltage) speeds up the XLPE insulation degradation, reducing the reliability and service life of cables. Its degradation is also accelerated in case of inadmissible increase of the amplitudes and frequency of harmonic voltages and test duration.

Therefore, a new concept of nondestructive diagnosis of high-voltage cables with XLPE insulation has been developed. In this concept it is determined that such cables not expediently, and cables of 110 kV and higher is absolutely not admissible to test with direct voltage.

It is proved, that the use of alternating voltages of industrial frequency (50 Hz) is possible if they exceed the operational voltages no more than 1.5 times at the test duration of just made cables less than 30 minutes, and the aged cables (i.e. cables, which were in operatione) less then 15 minutes.

For the practical implementation of the concept we developed the circuit diagram and the mathematical model of the resonant installation. Using these diagram and model we determined the modes of installation blocks for generation of low-frequency (50 Hz) voltage to 160 kV and decrease conditions of input power and short circuit currents 20-60 times at electric breakdowns of cables insulation. Results implemented at the plant "Pivdenkabel" at creation of installation for diagnostic just made cables with XLPE insulation for voltages up to 110 kV.