Detection of electrical corona on low frequency radio transmit antenna systems

Low frequency radio transmitting antennas are used for a variety of applications in marine navigation and submarine communications. In many applications, the limiting output power of the antenna system is determined by the onset of electrical corona, which occurs on antenna elements where electric fields are very high. The corona is extremely damaging to antenna components and drains power from the transmitted signal. The authors discuss electrical corona phenomena, research work done on measurement of signal characteristics of corona onset, and the potential for utilizing frequency domain analysis of antenna current signals for corona onset detection. The method is based on the fact that a corona discharge will excite harmonics of the fundamental frequency being applied to the antenna. It is demonstrated that shunt capacitance between the corona discharge site and the sensor position will make detection of corona very difficult if the sensors are placed outside the corona region. This suggests that sensors with very high dynamic ranges will be required if they are placed some distance from the suspected corona sites