To reduce power loss in long-distance DC cable transmission, a multi-dimensional technical system needs to be built, encompassing voltage level upgrades, current density control, operational optimization, conductor material improvements, insulation design enhancements, converter station efficiency improvements, and the application of intelligent monitoring technologies. This system combines physical characteristic optimization with intelligent control methods to achieve a systematic reduction in losses.
Increasing the DC transmission voltage is the core means of reducing losses. According to Joule's law, line resistance loss is proportional to the square of the current. When the transmission power is constant, increasing the voltage significantly reduces the current intensity. For example, increasing the voltage level from ±500kV to ±800kV reduces the current by 37.5% while transmitting the same power, resulting in a substantial decrease in line resistance loss. This technical approach has been widely used in UHVDC projects, overcoming the economic bottleneck of long-distance transmission by increasing the voltage level.
Precise control of current density is crucial for loss suppression. With a fixed conductor cross-sectional area, current density is positively correlated with the line loss rate. By adopting a split conductor structure or increasing the conductor cross-sectional area, the current distribution can be effectively dispersed, reducing the current density per unit area. For example, the four-split conductor design can reduce current density to one-quarter that of a single conductor, while also reducing corona discharge and further reducing reactive power losses. Furthermore, dynamically adjusting current density to match load demand avoids additional losses caused by excessive current density during low-load periods.
Optimized operating modes can significantly improve transmission efficiency. Bipolar parallel operation, by sharing a neutral line, reduces line losses by approximately 30% compared to monopolar operation. This mode has become standard in ±800kV UHVDC projects, its advantage being the balancing of currents between the two poles, reducing neutral line current and thus lowering overall losses. In addition, the use of flexible DC transmission technology, through power electronic devices to achieve rapid power regulation, can further optimize power flow distribution and reduce increased losses due to line overload.
Improved conductor materials provide the material basis for loss reduction. Copper conductors, due to their low resistivity and excellent conductivity, have become the preferred material for high-voltage DC cables. Compared to aluminum conductors, copper conductors can reduce resistance losses by more than 40%. In the field of superconducting technology, the zero-resistance characteristic of high-temperature superconducting cables can completely eliminate resistance losses. Although the current cost is relatively high, it has shown application potential in urban power grid capacity expansion and upgrading. For example, a superconducting cable demonstration project in Shenzhen achieved the same transmission capacity as traditional cables, but with losses reduced by more than 70%.
Strengthening insulation design is a key aspect of ensuring transmission efficiency. The insulation layer of DC cables must withstand the space charge effect under a DC electric field. Insufficient insulation performance can easily lead to partial discharge, resulting in increased energy loss. By using new insulation materials such as cross-linked polyethylene (XLPE) combined with nanocomposite technology, the dielectric strength and anti-aging performance of the insulation layer can be significantly improved, reducing leakage losses. In addition, optimizing the ratio of insulation layer thickness to conductor cross-sectional area can reduce insulation losses while ensuring safety.
Improving the efficiency of converter stations directly affects overall transmission losses. DC power transmission requires AC-DC conversion through converter stations, and the power loss of converter stations accounts for 15%-20% of the total system loss. Voltage source converter (VSC) technology can replace traditional thyristor converters, reducing conversion losses by more than 50%.
VSC technology achieves flexible power control through high-frequency switching devices, reducing reactive power loss and improving system response speed, providing a more efficient energy conversion solution for long-distance DC transmission.
The application of intelligent monitoring technology supports dynamic loss management. By deploying a distributed fiber optic temperature measurement system along the cable line, the line temperature distribution can be monitored in real time, promptly identifying localized hotspots and preventing increased resistance and losses due to temperature rise. Furthermore, combined with big data analysis technology, line loss prediction models can be established, dynamically adjusting operating parameters based on meteorological conditions, load changes, and other factors to achieve precise loss control. For example, a State Grid UHVDC project, through an intelligent monitoring system, has controlled line loss fluctuations within ±0.5%, significantly improving transmission efficiency.
