Numerical Analysis of Thermo-Electric Field for AC XLPE Cable in DC Operation Based on Conduction Current Measurement

Abstract

With rapid development of renewable energies and dc loads in distribution grids, converting ac distribution grids into dc operation has become a promising method to utmost utilize the present ac distribution grid in large cities. This paper reports a numerical investigation of thermo-electric fields of a three-core 10-kV ac cross-linked polyethylene (XLPE) cable and cable joint in the dc operation. DC conduction current for the XLPE and silicon rubber (SiR) was evaluated at different temperatures and electric fields. The thermo-electric field simulation was performed by COMSOL Multiphysics according to the measured data. The obtained result showed that the threshold of XLPE at 65 • C is 3.1 MV/m, whereas the threshold of SiR at 60 • C is 2.2 MV/m. It was found that the maximum electric field of the cable operated in dc voltage up to 12.5 kV was below the threshold of 3.1 MV/m. The maximum electric field in the cable joint appeared at the high voltage screen tube, whereas the maximum electric field at the high voltage screen tube was less than the threshold of SiR at a temperature difference of 25 • C. Moreover, the maximum transmission power of the three-core 10-kV AC XLPE cables running at the ±10-kV bipolar dc operation was 1.36 times of the power in the ac operation. It was elucidated that the three-core ac 10-kV XLPE cable could be operated reliably at ±10 kV in bipolar dc topology with sufficient safety margin. It is beneficial to upgrade the ac distribution grid to the dc distribution grid.INDEX TERMS XLPE cable, cable joint, bipolar DC operation, conduction current, space charge, thermo-electric field.

Thermo‐electric field analysis of AC XLPE cable in monopole, bipole, and tripole DC operation modes

“…The threshold of the 35 kV XLPE was consistently decreased with an increase of the temperature. Moreover, the electric field thresholds for the 10 kV AC XLPE materials are also shown in Table 4 according to the data reported in [13]. It could be seen that the threshold of the 35 kV XLPE was higher than the 10 kV XLPE at the same measured temperatures.…”

“…Detailed information about the DC conduction current measurement system was described in [13]. The conduction current of the 35 kV XLPE was recorded for 30 min under 2–20 MV/m with controlled temperatures of 30, 40, 50, 60, and 70°C, respectively.…”

“…Chen et al [13] presented a numerical analysis of thermo‐electric field for the 10 kV AC XLPE cable in the bipole DC operation. The feasibility and benefits of converting the 10 kV AC cable into ± 10 kV DC application were evaluated.…”

“…Moreover, the thermo‐electric field of the AC cable in different DC operation modes was also not compared. As reported in [13], space charges would accumulate in the insulation of the AC XLPE cable in the DC operation, leading to considerable endurance problems for the cables [14]. In order to avoid the problem of accelerated insulation aging caused by space charge accumulation, the electric field in the AC XLPE cable in DC operation should be limited to below the electric field threshold of space charge accumulation [13–15].…”

Temperature Analysis Based on Multi-Coupling Field and Ampacity Optimization Calculation of Shore Power Cable Considering Tide Effect

“…The calculation of cable temperature mainly includes the electromagnetic-thermal coupling and the thermal-flow coupling. Many scholars [12][13][14][15] have studied the electromagnetic thermal flow coupling model of the cable to calculate the flow field and temperature field distribution of the cable accurately. The purpose of calculating the cable temperature is to accurately calculate the ampacity of the cable.…”