Simulation Study on Impedance Spectroscopy of Cables of Various Aging Statuses and with Local Defects

Existing cable insulation condition assessment technologies, such as Dielectric Loss (tanδ) measurement and Partial Discharge (PD) Monitoring can only reflect the integral condition of, or local defects in, a cable circuit. From late 1990's, the cable impedance spectroscopy (CIS) method, a measure of the magnitude and phase angle of impedance over a range of frequencies, has been explored for cable condition assessment and fault detection. The paper aims to build on previous research and present an in-depth study of the CIS method for use in condition assessment of total insulation and to investigate its ability to detect and locate the positions of local defects. Simulation results indicated that the objectives can be achieved via CIS. General insulation aging and local defects both cause decreases in the amplitude of cable impedance and increase or shift in the phase of cable impedance. General aging of insulation and the existence of local defects can be distinguished via the rate of decline of the magnitude of CIS. By comparing the integral operations on the CIS results of a healthy cable and the ones having a insulation of general aging and with defects at a series of pre-set locations, criteria are established to locate local defects.