Extraction of cable joints tangent delta from bulk tangent delta measurement using HFAC method

• Main Authors: Shafi, H., Anthony, T.M., Basri, A., Raj, A., Chakrabarty, C.
• Format: Conference Paper
• Language: English
• Published: 2018

Tangent delta measurement is a well-known diagnostic used by many utilities for condition assessment. Guides on field diagnostic testing are well established by North American society through IEEE standards and guideline. Tangent delta, also called loss angle or dissipation factor (δ) measurement, is a diagnostic method of testing underground cables to determine the quality of the cable insulation in which value from the measurement will be used to compute dielectric loss within the cable insulation system. The higher the dielectric loss thus creates higher localized heating which leads to insulation degradation. However, dielectric loss measurement test technique is a global or bulk insulation condition assessment. It gives an overall condition of the complete cable system that includes cable, joints and terminations. A good dielectric loss result thus means that the overall condition of the complete cable system is in good condition whereas such high dielectric loss will just give unhealthy indication of the overall condition of the cable without revealing the weakness component within the insulation system. It is important to distinguish the dielectric loss of cable and its accessories within the system for the ease of maintenance works and such knowledge is an added advantage and greatly needed by the network owner. This paper presents the method of determining the tangent delta of cable joint from the total overall or bulk tangent delta measurement by using higher frequencies (>100Hz) at voltages above 1 kV. In this direct measurement method, the current (I), voltage (V) and phase (θ) were obtained by connecting a linear high voltage probe across the cable cross-section. The phasor diagram is then constructed and by some trigonometric exercises the actual phase across the joint is extracted. Hence, the tangent delta values were calculated. © 2016 IEEE.