Measurement of High-Current Impulses

Abstract

For the conventional measurement of impulse currents during tests of power apparatuses up to a few 100 kA, low-ohmic resistors or magnetic coils are used in combination with digital recorders enabling computer-aided processing of the recorded data. The theoretical background, different constructions of measuring resistors and coils, the measuring circuits, their advantageous and disadvantageous are described in detail. The requirements on approved measuring systems and reference systems as specified in IEC 62475 are given. The current to be measured generates a magnetic field, by which interference voltages can be induced in coaxial cables and measurement loops. Interference is avoided by special means, e.g., by using double-shielded measurement cables and installation of the recorder in a Faraday cage. Furthermore, the magnetic field causes skin effect in tubular shunts and thus, a limitation of their bandwidth. Depending on the type of the magnetic coil used, integration of the output voltage is essential before data processing. Integration can be achieved either by hardware or by software as is shown on the example of a Rogowski coil. With sensors working on the basis of the Hall effect, currents up to a few 10 kA can be measured. The future application of magneto-optic sensors, whose measuring principle is based on the Faraday effect, is promising. However, their application for impulse current measurements is still in the experimental stage.