Effects of Lightning Electromagnetic Pulse and High Power Microwaves on Military Electric Systems

Sammanfattning: The awareness of the threat posed by Lightning Electromagnetic Pulse (LEMP) and High Power Microwaves (HPM) against the operational reliability of electric systems is rapidly growing. This has led to an increasing need for reliable tools, experimental as well as theoretical, for design, analysis and verification of system immunity against electromagnetic threats. This thesis presents four main studies of electromagnetic interaction:Firstly, we present measurements of common-mode (CM) voltages induced in a residential low-voltage power installation (LVPI) network exposed to LEMP. The sequences of induced voltage events during the complete duration of a negative cloud-to-ground (CG) flash, a positive CG flash, and a cloud flash (CC) are presented simultaneously with the incident electric field. In addition to the return strokes in CG flashes, we found that other discharge events, notably the bipolar pulse trains associated with the initiation of both CG lightning and cloud lightning, determine the transient lightning electromagnetic environment of electric systems and components.Secondly, the induced voltages due to broad and narrow impulse current injection into the shield of 48 m long signal and power cables were studied in order to simulate the coupling of LEMP to shipboard cable networks. Single- and multi-point grounding were studied for proposing an appropriate grounding philosophy for ships.Thirdly, we have studied microwave, 0.5 to 18 GHz, field-to-wire coupling for some basic wire geometries in Anechoic Chamber (AC) and Reverberation Chamber (RC). Receiving parameters, such as the antenna receiving cross section, σw, and the effective antenna length of the wire, he, are presented. The ratio between the maximum and average values of σw may exceed 10 to 15 dB in the AC, the average being equal to σw measured in the RC. These large variations of σw measured in an AC, as a function of the direction and polarization of the incident field, imply a substantial risk for obtaining too low values of σw since, for realistic radiated susceptibility (RS) tests in an AC, only a few angles of incidence can typically be afforded. Furthermore, σw measured in the RC follows a χ2-distribution with two degrees of freedom, which it does not do in the AC. Fourthly, we present measurements of microwave field-to-Printed-Circuit-Board coupling for single-sided PCBs, double-sided PCBs and multi-layer PCBs performed in RC. Receiving parameters are presented. σw measured for PCBs in the RC is found to follow a χ2-distribution with two degrees of freedom. The impedance-matched σw is bounded by λ2/8π. he of the traces on the PCBs is found to be roughly bounded by the wavelength λ.