*Article* **E**ff**ect of Polycyclic Compounds Fillers on Electrical Treeing Characteristics in XLPE with DC-Impulse Voltage**

#### **Lewei Zhu 1,2, Boxue Du 2,\*, Hongna Li 1 and Kai Hou 2**


Received: 27 June 2019; Accepted: 16 July 2019; Published: 18 July 2019

**Abstract:** Electrical tree is an important factor in the threat of the safety of cross-linked polyethylene (XLPE) insulation, eventually leading to the electrical failure of cables. Polycyclic compounds have the potential to suppress electrical treeing growth. In this paper, three types of polycyclic compounds, 2-hydroxy-2-phenylacetophenone, 4-phenylbenzophenone, and 4,4-difluorobenzophenone are added into XLPE, denoted by A, B, and C. Electrical treeing characteristics are researched with DC-impulse voltage at 30, 60, and 90 ◦C, and the trap distribution and carrier mobility are characterized. It has been found that although three types of polycyclic compounds can all suppress the electrical tree propagation at different voltages and temperatures, the suppression effect of these polycyclic compounds with the same DC-impulse polarity is worse than with the opposite polarity. As the temperature increases, the suppression effect becomes weak. The energy level and deep trap density are the largest in XLPE-A composite, leading to a decrease in the charge transportation and resulting in the suppression of electrical treeing growth. Experimental results reveal that the polycyclic compound A has grea<sup>t</sup> application prospects in high voltage direct current (HVDC) cables.

**Keywords:** electrical tree; XLPE; polycyclic compound; DC-impulse voltage; temperature; trap distribution
