Experimental study on cable coupling effects of lightning strikes on a metal mast

Abstract

[Objective] This paper carries out an experimental study on the coupling response characteristics of the internal cables of a metal mast when struck by lightning. [Method] A lightning induction coupling test platform is built for the cable system inside the mast. The induced voltages of the coaxial cables, two-core single shielded cables and multi-core double shielded cables are measured under four kinds of termination load characteristics (open circuit at both ends of core wire; end of core wire near to the ground connected to the load; end of core wire far from the ground connected to the load; and both ends of core wire connected to the load). From the perspective of time domain and frequency domain, an analysis is made of the influence of load characteristics on the induced voltage and shielding effects. [Results] The induced voltage of the cable reaches its maximum value when the far ground terminal is grounded by the load. When the near ground terminal is grounded by the load, the main frequency band of the induced voltage frequency response exceeds the lightning current, whereas they are similar under other load characteristics. Grounding the inner shielding layer can reduce the peak value of the induced voltage, but does not affect the main frequency band of the frequency response. The voltage peak value is most significantly reduced when both ends of the core wire are open-circuited or when the end of the core wire far from the ground is connected to the load (approximately 59.3% and 77.2% of the value when the inner shielding layer is ungrounded). In addition, the induced voltage peaks of the three types of cables exhibit considerable differences. However, the rise time and half-peak time of the induced voltage for each cable show insignificant differences. [Conclusion] This study reveals the influence of terminal load characteristics on cable coupling induced voltage when lightning strikes the metal mast of a ship, as well as providing basic data support for the subsequent calculation of the coupling effect.

Keywords

• metal mast
• cable coupling
• termination load characteristics
• lightning current waveform
• induced voltage