Parasitic Magnetic Coupling in Voltage Measurement Setups for Impulse Current Tests

Voltage measurement setups for impulse current tests have to deal with the unintended coupling of magnetic fields into the test probes. As a result induced voltages can lead to a misinterpretation of the measured voltage curve which is essential for the whole development process of components like surge protective devices (SPD). To investigate the influence of the magnetic coupling a test setup, consisting of a surge current generator and a conductor arrangement representing the device under test (DUT), is implemented. A printed circuit board (PCB) with different conductor loops specifically designed for the investigation is used as a probe to measure the voltage drop across the conductor. Additionally, the conductor loops provide a well-defined coupling behaviour. The area which is permeated by the magnetic flux can be adjusted in order to evaluate the influence of the conductor loop-area on the induced voltage. Furthermore, the injected impulse current is varied to analyse the effect of the respective current value on the parasitic coupling in the measurement setup. For a deeper understanding of the magnetic coupling behaviour a field simulation of the test setup is carried out. The parametrised simulation model is validated by the respective measurements. In further studies the obtained results could be used for a more exact determination of the voltage drop solely across the DUT due to the fact that the parasitic induced voltages can be considered separately in the simulation process.