Characteristic Impedance Modeling of Nuclear Power Instrumentation and Control Cable Shield Breakage

Nuclear Instrumentation and Control (I&C) cables laying in a complex environment are prone to shield damage. And, the traveling wave reflection method can be used to detect and locate damage using the characteristic impedance change caused by I&C cable damage. Therefore, this paper establishes a quasi-coaxial cable shield characteristic impedance calculation model. And, it brings in the defective circumferential angle of the damage coefficient. Then, it builds a quasi-coaxial I&C characteristic impedance model approximation of the multi-core cable structure combined. Finally, the results of this paper through calculations and simulations are as follows. Firstly, the characteristic impedance of the cable with eccentricity e equal to 2.57 mm is stabilized at 37.795 Ω with increasing frequency. Second, the difference in the computational model is 3.88 Ω at 10 MHz of frequency, and a less than 3% difference in model approximation of a four-core cable at 5 MHz of frequency. Third, the calculation model can control the error of the characteristic impedance calculation result within 4 Ω within the defect angle of 270°. These results validate the reasonableness of the model.