Predicting Fatigue Damage and Vulnerability of a Shunt Reactor Due to Structural Vibrations

In this work, an actual failure case of a 50MVAr, 245kV, three-phase oil filled Shunt Reactor has been assessed. In this unit, multiple weld-cracks were observed in tank body and clamping structure. Investigation of manufacturing and test records confirmed that these failures were not related to workmanship and manufacturing quality. This led to a detailed vibration-fatigue investigation. As a result, a vibration-fatigue assessment technique is developed and applied that enables the designers to predict fatigue damage, crack initiation and propagation in welded structural parts of a Shunt Reactor. This novel approach integrates vibration data, electromechanical excitation mechanisms, 3-D finite element analysis and fracture mechanics based crack growth simulation and analysis.

Vibration measurements were collected and referenced to validate the numerical model.

Loading criteria derived from Maxwell forces and magnetostriction forces were considered as vibration source. Harmonic, modal and random vibration simulations were carried out to evaluate structural frequency response and stress distributions across the steel structure. Paris’ law was then used with region-specific material parameters for base metal (BM), weld metal

(WM) and heat affected zone (HAZ) to evaluate fatigue crack growth in the identified highstress zones. The results show that weld metal regions show significantly lower fatigue resistance as compared to base metal and heat affected zones. Once crack is initiated, crack propagation is observed to accelerate rapidly under continuous cyclic vibration loads from 0.1 mm to more than 4.0 mm within a small cycle range. Random vibration analysis identifies critical weld locations with cumulative damage values as high as 0.52, clearly indicating fatigue-critical regions within the clamping structure.

The proposed methodology enables early identification of vibration-sensitive weld locations during the design stage and provides a practical tool for failure prevention, design improvement, and inspection planning of high-voltage shunt reactors. By directly linking field vibration measurements to fatigue crack growth behaviour, this work fills an important gap in structural integrity assessment of shunt reactors under operational vibration conditions.