Eddy current testing of the side walls of current-carrying joints of stators of electric machines accounting for the interfering factors

Eddy current testing of the quality of soldering of current-carrying joints of stators of hydro- and turbogenerators is carried out when commissioning new units, as well as after their scheduled repairs. The objective of this study is to investigate the specific electrical conductivity of connecting strips of current-carrying joints made of M1 copper semi-finished products and to eliminate the influence of adjacent joints on the testing results. When hot-rolled busbars are used as connecting strips in current-carrying joints of turbogenerator stator windings, significant variability (from 2 to 4.4%) in their electrical conductivity across their thickness and from product to product is observed. The error in determining the solder integrity of sidewalls using an eddy current transducer (ECT) can reach 52.8%. This must be taken into account when developing eddy current testing tools for soldering such joints, with electrical conductivity determined at the same frequencies at which the testing will be performed. It has been demonstrated that conductivity variability does not affect solder quality testing results when inspecting current-carrying joints in hydrogenerator stator windings, as the current-carrying rods and connecting strips in this case consist of soft copper busbars manufactured from rod using the upward casting method. However, the influence of adjacent connections on the ECT signals is significant. A method for eliminating this influence is proposed, consisting of shielding the ECT windings with a two-layer screen made of transformer steel. The obtained results can be used to improve the reliability of solder joint inspection in power equipment and to refine the methodology for use with other types of connections, as well as in conditions of complex electromagnetic interference.

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