Critical Review of Voltages Applied for Quality-Acceptance and Diagnostic Field Tests on High-Voltage and Extra-High-Voltage Cable Systems

Extruded cable systems are assembled on site. The quality of their components (cable lengths, joints, and terminations) is carefully verified by quality-acceptance tests in the factory (prequalification tests, type tests, and routine tests). These tests are completed by a quality-acceptance test in the field, which verifies the quality of the cable system under service conditions. After the successful commissioning, the cable system is handed over from the supplier to the user. During the decades of operation of the cable system, off-line diagnostic field tests including PD, dielectric measurements, or both are useful for condition assessment of the insulation. The complexity of diagnostic methods demands the application of knowledge rules and has not so stringent requirements to test voltages as qualityacceptance tests. Often the differences between quality-acceptance and diagnostic field tests are not clear. In the following, the suitability of the usual test voltages, applied for extruded cable systems in the field, will be investigated for both, for quality acceptance during commissioning and for condition assessment during operation. The comparison has to consider the remarkable differences of the design field strength of medium-voltage (MV) cables on the one and high-/extra-high-voltage (HV/EHV) cables on the other side. Often no quality-acceptance tests on MV cable systems are performed with separate test-voltage sources, but a great variety of diagnostic off-line tests is applied. The practice of MV cable systems should not simply be transferred to HV/ EHV cable systems. Therefore, this investigation is limited to HV/EHV cable systems, which are of increasing importance for power systems. It has to be mentioned that there is no sharp limit between the MV and HV/EHV range; it shall be assumed in the range of rated voltages between 50 and 72.5 kV. © 2006 IEEE.