Investigation of GPT Phase Angle for Tan δ Measuring Method of Hot-Line Power Cable

Abstract

As a diagnostic apparatus of deterioration of 6kV class XLPE cable on the hot line, a practical apparatus has been developed, which detects the voltage signal from a potential divider contacted with a high voltage live part and the charging current from a grounding conductor current and displays tan δ and electrostatic capacity. The authors have investigated the various methods, which are adopted to the state of cable line, in order to find the most important input procedure of the voltage signal for the application of this apparatus in the work site operation. We have proposed a method of using the secondary voltage of the GPT (ground potential transformer), which are installed especially at the many places such as substations and the like, and have developed and proved the method. We can expect that it can be applied not only for the 6kV class XLPE cable but also in the broad areas such as the continuous monitoring system for the cable and electrical equipments because it has outstanding properties especially in safety, operability and so on.
The following items are discussed in this paper:
(1) development of the new method/program, which can calculate the phase difference (phase angle) between the primary and secondary voltage signals of GPT, (2) method/equipment for measuring the burden of GPT, which is required for calculation of the phase angle, and the measuring results, and (3) the proven results in the field.