Study on Development Characteristics of Cavity Discharge in Composite Insulation of Superconducting Cable

Abstract

Superconducting cable is a promising application in future power transmission systems due to the advantage of low power loss, compact dimensions and large current capacity. Cavity discharge is a common defect during cable manufacturing and transportation, which might cause severe damage to superconducting cable. Therefore, cavity discharge characteristics in superconducting cables should be further studied before large scale industrial applications. In this paper, experimental platform was proposed and pulse current method was employed to study the development characteristics of cavity discharge of composite insulation immersed in liquid nitrogen. In the experiment part, a constant temperature and pressure experimental platform was designed and cavity defect specimen were made to simulate the actual operating environment superconducting cable's insulation. Step-up voltage method was used to for specimen testing and discharge signal was collected on each voltage step until breakdown. Accordingly, Q-φ-n three-dimensional graphs of cavity discharge were drawn and typical characteristic parameters were extracted from graphs in the analysis. Results is shown as follows: With the development of cavity discharge of composite insulation at the liquid nitrogen temperature, average amplitude and show a trend of slowly increasing at the beginning stage after initial, decreasing at the medium stage, and increasing dramatically at the before breakdown. Also, discharge phase is gradually widened to 0 ° and 180 ° while discharge initials around 90° in positive half cycle and 270 ° in negative half circle. According to the discharge features, the entire process of cavity discharge in composite insulation of superconducting cable can be categorized into 4 stages by clustering analysis. The study of cavity discharge characteristics might provide a better vision on the understanding and diagnosis of superconducting cable's health statue.