The use of a three-phase eddy current flaw detector to control the continuity of the material

The use of single-element eddy current transducers in eddy current testing devices limits the flaw detector performance, since the formed eddy current contour corresponding to the average turn of the eddy current transducer coil is limited by the area of this turn and the scanning speed of the tested surface. The presence of several single-element eddy current transducers inevitably has a negative mutual influence. The paper presents the results of increasing the performance of a three-phase eddy current flaw detector (ECF), including increasing the scanning speed and reducing the mutual influence of single-element eddy current transducers. A three-element three-phase eddy current transducer is used as a source of the informative parameter in the ECF, represented by three single-element transformer transducers, the excitation windings of which are connected to a source of three-phase alternating high-frequency voltage. Based on the Wagner – Evans theory, a mathematical model is proposed that describes the formation of the so-called asymmetric system when the symmetry of a three-phase voltage system is violated. This system can be represented as a sum of symmetric components: direct, reverse, and zero sequences. Taking into account the mathematical model, a structural diagram of the eddy current tester has been developed. The diagram assumes that the exciting windings of the single-element converters that make up the flaw detector are connected to a source of three-phase symmetrical voltage, and the measuring windings receive the introduced voltage in the form of a three-phase system when the eddy current converter interacts with the test object. In addition, using a filter for symmetric components, the voltage of the reverse sequence is isolated, which is formed only when the symmetry of the introduced voltages on the measuring windings of the three-phase eddy current converter is violated and can be used as an informative parameter for detecting such defects as, for example, discontinuities in the test object. The obtained results can be used in eddy current flaw detectors based on electromagnetic non-destructive testing methods to detect defects of various natures.