What causes radio interference on high-voltage DC transmission lines?

The correct choice pertains to the pulses created by thyristor valves and corona discharge, which are significant factors contributing to radio interference in high-voltage direct current (HVDC) transmission lines.

Thyristor valves are semiconductor devices used to control the power flow in HVDC systems. They switch on and off rapidly, creating electrical pulses that can emit electromagnetic radiation. This radiation can manifest as radio frequency interference, which can disrupt radio communications and other electronic devices in the vicinity.

Additionally, corona discharge occurs when the electric field around high-voltage lines is sufficiently strong to ionize the surrounding air, producing a visible glow and generating a range of frequencies that contribute to radio interference. The combination of the fast switching of thyristors and the continuous nature of corona effects adds to this form of interference.

Understanding the causes of radio interference is critical in the design and operation of HVDC systems, as it helps engineers mitigate these issues through proper system design and equipment selection. The other factors mentioned in the other choices do contribute to various electrical phenomena but are not the primary sources of radio interference in this context. For example, current flow through converter stations is necessary for operation but does not inherently create interference on its own. Similarly, electrical discharge over the transmission line