HVDC Transmission Systems
HVAC v/s HVDC
In AC Transmission, the direction of voltage and current change continuously which causes overheating in the lines, thus resulting in significant power loss. Unlike AC transmission, current and voltage flow in one direction only in DC Transmission. So, when we convert HVAC into HVDC we observe a significant reduction in power loss hence increasing the efficiency of the transmission lines.
Comparison of AC and DC Transmission
The merits of two modes of transmission (AC & DC) should be compared based on the
1. Economics of transmission
2. Technical Performance
Classification of HVDC Links
The high voltage dc links may be classified into:
1. Monopolar Link: monopolar link has only one conductor and return path is provided by permanent earth or sea.
2. Bipolar Link: This is the most widely used dc link for overhead long-distance HVDC transmission systems and also for back-to-back HVDC system. This link has two conductors— one operating with positive polarity and the other with negative polarity with respect to the earthed tower structure.
3. Homopolar Link: A homopolar link has two or more conductors having the same polarity.