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Fibre optic based clamping force monitoring system for power transformers

The preservation of the initial clamping forces or mechanical stability of the power transformers during their whole active life in very different conditions appearing in operation (mechanical stresses during short-circuits, inrush currents and transportation, frequent heating/cooling processes, paper-oil moisture and ageing) has not been completely kept under control though in the technical literature there are presented and applied many on-line and off-line, intrusive or non-intrusive methods which by means of the offered results try to get into the “black box” represented by the transformer from this viewpoint. The paper present a new direct measuring system for the axial clamping forces of power transformer windings enabling an objective assessment of their mechanical stability. The system is based on an optical intrinsic technology with high electromagnetic compatibility and independent transducers which does not influence in any way the original mechanical / dielectric design of the transformer. There are presented the principle and application of these solution, the performed experiments and the application software enabling measured values correction depending on insulation condition at the measurement moment.