Wavelet aided monitoring of thermal ageing of thyristor working in AC regulator

Thyristors working in power converters tend to operate under thermal and environmental stresses which degrade their performance. If the degree of degradation due to such stresses remains undetected at its early stage, then critical processes may lead to unwanted shutdown and consequential economic loss. Work presented in this paper proposes a scheme to monitor the degree of degradation due to thermal stress experienced by thyristor working in an AC voltage regulator. A series of experiments have been performed on an implemented hardware circuit where a thyristor was subjected to operate under gradually elevated thermal stress till it failed. Load current signals were captured under different thermal stress conditions of the thyristor. Load and firing angles were also varied for comprehensive analyses of the thyristor characteristics under artificially imposed thermal stress conditions. Captured current signals under different operating conditions were then analyzed by employing continuous wavelet transform (CWT) as signal processing tool to extract suitable indictor of degree of thermal stress imposed on the thyristor. Results presented by analyzing load current signals have been found to be encouraging to assess the degree of performance deterioration of thyristor due to its operation under consecutive thermal cycles.