Risk Assessment and Mitigation Strategy of 120 lightly loaded Power Transformers Containing Dibenzyl Disulphide

The paper presents the mitigation strategy of 120 lightly loaded Power Transformers that contains Dibenzyl Disulphide and challenges in terms of failure probability, risk and reliability. A Case Study of the 120 transformers incorporates the guidelines in CIGRE WG A2.40 and applies a statistical method (Weibull distribution) to quantify the risk associated with lightly loaded HVPTs containing DBDS. The results from Insulating oil samples collected over three years were studied, in particularly, the significance of mercaptan, toluene, hydrogen sulphide, peroxide and depletion of DBDS to identify corrosion trends. Based on the failure rate of γ=0.12 % for the most affected batch of transformers from a specific Original Equipment Manufacturer compared to the overall affected population with a failure rate of γ=0.16 %, it is concluded that the risk of failure associated with DBDS is low. Four mitigation solutions were assessed and evaluated from a cost impact and efficiency perspective comprising passivation, oil replacement, selective depolarization and modified alumina-based sorbent. The paper demonstrates the viability of maintenance and risk mitigation strategies at attractive lifecycle cost combined with the collateral benefit of the proposed risk mitigation solution.