Examiner: Yuriy Serdyuk, Dept of Electrical Engineering
Opponent: Erik Andersson
In the modern society, complex electronic devices are widely used that, either intentionally or unintentionally, radiate signals imposing a risk of interferences with other electronics. To meet a growing urge for uninterrupted operation of electronic devices and systems, testing for approving sufficient electromagnetic compatibility are essential. Such tests, including radiated susceptibility tests, are described in the globally used military test standard MIL-STD-461G. This project aimed to develop a testbed for radiated susceptibility testing for objects sized up to 1x1x1 m3. The test procedure comprises generation of a high voltage pulse and injection of the pulse into a radiation system for creating a transverse electromagnetic field to which the test object is exposed. For the test to be valid, the electromagnetic pulse should provide the front time of maximum 2.3 ns, full width at half time of maximum 18-28 ns and the electric field amplitude of minimum 50 kV/m.
The testbed materiel produced within this project includes a radiation system constituted by a 3 m high transmission line composed by 21 conducting wires arranged in a parallel plate resembling structure, a water resistor to make a matched termination of the transmission line, a pressure vessel including a pulse trigger spark gap and field derivative sensors for measuring both electric displacement field and magnetic flux density. FEM based simulations were performed to verify design parameters of the transmission line and the spark gap.
In the experiments, a low inductance, 200 kV rated capacitor bank of 4 nF was charged with a voltage impulse of 900 ns front time originating from a Marx generator. Further, electromagnetic pulses were generated by rapidly discharging the capacitor bank into the transmission line via the pulse trigger spark gap enclosed in the vessel filled with SF6 gas at pressure up to 3 bar. Prominent scattering in the trigger voltage was observed, which probably was caused by impurities in the gas system. Electromagnetic pulses with the front time of 8 ns were successfully generated. The pulse amplitude of 173 kV was obtained, but only occasionally due to issues with external flashovers in the pulse generator. The amplitude of reliably repeatable pulses was 132 kV. Consequently, the electric field requirement of minimum 50 kV/m was not fully fulfilled that was shown by the compilation of the results from the electric field simulations and measured signal attenuation in the transmission line.
The analysis of the results suggests the ways for further improvements. Thus, it is found that the testbed premises (the high voltage laboratory with grounded walls, floor and ceiling) implicated undesired waves reflections, which need to be damped. Further, an evaluation of different measurement cables emphasized the need of using properly shielded cables to suppress noise level. Various types of transmission line termination resistors were tested and it was concluded that a water resistor was preferred as it features low inductance and its resistance value could easily be adjusted to make a properly matched termination. In addition, the used field sensors would need to be calibrated to give absolute values of the electric field amplitude.
Student project presentation
16 April, 2021, 14:00
16 April, 2021, 15:00