When a corona discharge occurs around a high-voltage conducting part of any equipment or around conductors, RIV appears. The corona discharge is nothing but a partial discharge that happens in the air surrounding a conductor at a high voltage level. This corona discharge creates electromagnetic waves of very high frequency. This high-frequency electromagnetic wave is in the range of kilohertz and megahertz. This high frequency electromagnetic waves may influence the radio communication system nearby. In other words, this high-frequency electromagnetic wave may create noise in the nearby radio and communication signals.
So, we can define Radio Interference Voltage (RIV) as the electrical noise produced by high-voltage equipment during corona or partial discharge phenomena that can disrupt radio and communication systems.
Very high-voltage conducting parts of transmission lines and equipment are the main source of RIV. Rough conducting surfaces under high-voltage stress and a humid atmosphere increase corona and hence RIV. Contaminants or damage in the insulation system can cause partial discharge. Obviously, this partial discharge also creates RIV.
Effects of Corona
However, corona is the main source of RIV. There are mainly three effects of corona.
Audible and Visual Effects: Corona produces hissing and cracking noises along with a visible glow on transmission lines.
Power Loss: Since corona is a partial discharge in air, it consumes electrical power. Therefore, it causes power loss in transmission systems.
Electromagnetic Interference: Corona generates very high-frequency electromagnetic waves that can affect nearby communication systems.
RIV is measured using a special measuring instrument connected to a coupling capacitor and a filter network. The meter measures interference voltage in microvolts at a specified frequency, commonly between 0.5 and 2 MHz.
RIV Test Procedure for HV Conductor
Generally, we measure RIV for 400kV systems and above. So, we go to the test for 400 kV conductors.
Here, we take two samples of conductors of a minimum 5-meter length each. We strung these conductors in a horizontal twin bundle configuration with a spacing of 450 millimeters between sub-conductors. We fit this arrangement with required insulators at a height not more than 8.84 meters above the ground. 8.84 meters is the ground clearance of 400 kV systems. Then we apply a 50 Hz 305 kV line to the ground power-frequency voltage under dry conditions to that bundle conductor arrangement.
After that, we measure the radio interference voltage with an RIV meter. If the measured RIV is below 1000 microvolts at 1 megahertz, the test is passed.
