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Option 4 : 1, 2 and 3
High voltage direct current (HVDC) power systems use D.C. for transmission of bulk power over long distances. For long-distance power transmission, HVDC lines are less expensive, and losses are less i.e. more efficient as compared to AC transmission.
Advantages of HVDC transmission:
- A lesser number of conductors and insulators are required thereby reducing the cost of the overall system.
- It requires less phase to phase and ground to ground clearance.
- Their towers are less costly and cheaper.
- Corona loss is less as compared to HVAC transmission lines of similar power.
- Power loss is reduced with DC because fewer numbers of lines are required for power transmission.
- HVDC system uses earth return. If any fault occurs in one pole, the other pole with ‘earth returns’ behaves like an independent circuit. This results in a more flexible system.
- HVDC acts as the asynchronous connection between two AC stations connected through an HVDC link, i.e. it interconnects two substations with different frequencies.
- Due to the absence of frequency in the HVDC line, losses like skin effect and proximity effect does not occur in the system.
- It does not generate or absorb any reactive power. So, there is no need for reactive power compensation.
- Very accurate and lossless power flows through the DC link.
Disadvantages of HVDC transmission:
- Converter substations are required at both the sending and the receiving end of the transmission lines, which result in increasing the cost.
- Inverter and rectifier terminals generate harmonics which is reduced using active filters which are also very expensive.
- The inverter used in Converter substations has limited overload capacity.
- Circuit breakers are used in HVDC for circuit breaking, which is also very expensive.
- It does not have transformers for changing the voltage levels.
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