Assessment on capacity expansion of AC XLPE cable under DC operation with the constraint of temperature and electric field intensity

Abstract

The effective design of controlling parameters in AC–DC conversion in power cables has played an important role in transmission security. The state-of-the-art studies determining the voltage level and ampacity of cables are mostly based on the core temperature at 70 ℃. Accordingly, this paper proposed a technique to determine the cable DC voltage level and ampacity of AC–DC conversion by taking operational temperature, the steady and the transient state electric field intensity constraints and the critical reversal temperature difference (CRTD) into account. The results of the research indicated that the voltages of 66 kV AC cable can be transformed to ±55 kV, ±50 kV and below, the voltages of 35 kV AC cable can be transformed to ±50 kV, ±30 kV and below, the voltages of 10 kV AC cable can be transformed to ±20 kV, ±10 kV and below. Although one of three phases is idle, the capacity of transmission line has improved effectively, and the idle phase could be an alternate to enhance the reliability. Compared with AC operation, the maximum transmission capacity of DC operation increased on different levels. The design results and the approaches of AC-DC conversion in this paper can contribute a valuable recommendation to the electrical engineering field.