Risk Based Inventory Management of EHV Equipment Through Failure Modes and Effects Analysis

Conventional spare parts inventory practices in transmission utilities are generally based on equipment population or voltage class and often do not adequately consider component-level failure risk, leading to either excess inventory or insufficient availability of critical spares. This paper proposes a risk-based inventory management approach for EHV substation equipment based on Failure Modes and Effects Analysis (FMEA). The methodology integrates operational failure experience, life-cycle effects, and structured risk evaluation to support risk-informed inventory allocation. The approach is demonstrated using failure data of our organisation. The study primarily focuses on circuit breakers, while the proposed methodology is applicable to other substation equipment such as CTs, CVTs, etc. Actual failure data of 219 circuit breakers with service age of up to 25 years were used. Based on analysis of these data, ten major circuit breaker components were identified as significant contributors to failures. Conventional FMEA was applied to these components to identify failure modes, failure causes, and failure effects.

Risk assessment was carried out using occurrence, severity, detectability, and ageing parameters, which were combined to compute the Risk Priority Number (RPN) for individual components. The resulting RPN values enabled systematic ranking of component-level risks.

Based on the RPN-based classification into Low, Medium, and High risk categories, an inventory allocation matrix was developed to align spare provisioning with assessed risk levels. This matrix provides guidance on standard, limited buffer, and critical buffer inventory strategies to support effective restoration and optimized spare management. The proposed framework demonstrates that FMEA-based risk assessment can be effectively used to support risk-informed inventory management for EHV substation equipment. The approach enables prioritization of critical components, optimization of spare inventory, and improved asset management, and can be extended to other substation equipment within transmission networks.