High Voltage Direct Current (HVDC) Transmission

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 as compared to AC transmission. It interconnects the networks that have different frequencies and characteristics.

In AC transmission, alternating waves of voltage and current travels in the line which change its direction every millisecond; due to which losses occur in the form of heat. Unlike AC lines, the voltage and current waves don’t change their direction in DC. HVDC lines increase the efficiency of transmission lines due to which power is rapidly transferred.

How does HVDC transmission system work?

In generating substation, AC power is generated which can be converted into DC by using a rectifier. In HVDC substation or converter substation rectifiers and inverters are placed at both the ends of a line. The rectifier terminal changes the AC to DC, while the inverter terminal converts DC to AC.

The DC is flowing with the overhead lines and at the user end again DC is converted into AC by using inverters, which are placed in converter substation. The power remains the same at the sending and receiving ends of the line. DC is transmitted over long distances because it decreases the losses and improves the efficiency.

Advantages of HVDC transmissions

»    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.

»    Power loss is reduced with DC because fewer numbers of lines are required for power transmission.

»    The 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.

»    The very accurate and lossless power flows through DC link.