1. Different Utilization Systems:
DC cables are used in direct current transmission systems after rectification, while AC cables are commonly used in power systems operating at the industrial frequency (50Hz).
2. Lower Energy Loss in Transmission:
In comparison to AC cables, DC cables exhibit smaller energy losses during the transmission process. The energy loss in DC cables is primarily due to the direct current resistance of the conductors, with insulation losses being relatively small (dependent on the magnitude of current fluctuations after rectification). On the other hand, the AC resistance of low-voltage AC cables is slightly larger than the DC resistance, and for high-voltage cables, losses are significant due to proximity effect and skin effect, where insulation resistance losses play a major role, mainly generated by impedance from capacitance and inductance.
3. High Transmission Efficiency and Low Line Loss:
DC cables offer high transmission efficiency and minimal line losses.
4. Convenient for Adjusting Current and Changing Power Transmission Direction.
5. Despite the higher cost of conversion equipment compared to transformers, the overall cost of using DC cables is much lower than that of AC cables. DC cables are bipolar, with a simple structure, while AC cables are three-phase four-wire or five-wire systems with high insulation safety requirements and a more complex structure. The cost of AC cables is more than three times that of DC cables.
6. High Safety in the Use of DC Cables:
- Inherent characteristics of DC transmission make it difficult to induce current and leakage current, avoiding electromagnetic interference with other co-laid cables.
- Single-core laid cables do not experience magnetic hysteresis losses due to steel structural cable trays, preserving cable transmission performance.
- DC cables have higher short-circuit and overcurrent protection capabilities.
- When the same voltage electric fields are applied to insulation, a DC electric field is much safer than an AC electric field.
7. Simple Installation, Easy Maintenance, and Lower Costs for DC Cables.
Insulation Requirements for the Same AC and DC Voltage and Current:
When the same voltage is applied to the insulation, the electric field in DC cables is much smaller than in AC cables. Due to the significant structural differences between the two fields, the maximum electric field during AC cable energization is concentrated near the conductor, while in DC cables, it mainly concentrates within the insulation layer. As a result, DC cables are safer (2.4 times) when the same voltage is applied to the insulation.
Post time: Nov-10-2023