Integral condition assessment by dielectric response diagnosis of service aged external gas pressure HV power cables

Already existing knowledge about aging phenomenon in type insulated power cables as well as measuring criteria has been continuously improved during last 20-30 years. Nowadays many HV power circuit with paper insulation reach their end of service life time due to extensive deterioration of insulation under high operational temperatures and electrical, mechanical overstressing. Growing demand of energy market for new sources of energy and increment of current loads on existing serviced HV power transmission cables change aging rates and lead to often unexpected failures. Accelerate in this way insulation deterioration processes in many cases need new interpretation of diagnostic parameters related to aging of cable insulation to support condition assessment decision and foreseen failure development. Additionally when costs of repairs, cable replacement and customer claims due to breakdown and blackouts are taken into consideration, finance balance for the repair of a single failure in a 150 kV link can costs around 75 kC. For this reason reliable judgment of actual cable condition with available on market diagnostic methods is in great of importance from utility point of view. In this contribution effort was put to estimate actual service condition of four sections of external gas pressure 110 kV-150 kV power cables with two integral diagnostic methods. Interpretation of diagnostic data has been done with aspect to several diagnostic parameters. All relevant diagnostic parameters were obtained during on-site tests in with low-voltage method based on recovery voltage phenomena and high voltage method based in DAC voltages to estimated dielectric losses.