Mapping as risk and cost assessment methodology
Proactive transformer mapping assists in operational and financial decision-making
Our January 2020 article  focused on the use of the mapping process as a starting point to determine the appropriate remediation and conservation measures that your maintenance team needs to take to ensure a transformer block subjected to accelerated aging performs over the long-term. This article expands on mapping and risk assessment to identify the actions required to extend the operating lifetimes of transformers subjected to other forms of risk, such as design and random external risks. In cases of these risks, the mapping process generates different remediation and conservation strategies to ameliorate and control them. These strategies are then compared so that the option that best balances risks can be implemented with an evaluation of operational and financial considerations. We use a hypothetical example, based on typical field experience, to illustrate these concepts.
Mapping is a robust, proactive process that provides an overall picture of potential risks and worst-case scenarios, including financial risks and cost comparisons
2. Types of risk
A transformer block is a complex system. The transformers and auxiliary equipment that comprise an operating block are interconnected and must function as designed for the block to meet operational objectives over an extended period. The issues of accelerated aging and its effect on premature failure have already been addressed in previous articles. A transformer block can also be at risk due to poor design and / or workmanship that create functional weaknesses in a transformer. These, in turn, can cascade throughout the system to cause outages, fires, or other system performance issues in the transformer block. Defects, such as poor welded joints or a defective head gasket sealing, can increase the risk of failure of an individual piece of equipment or the entire transformer block. Random factors, such as lightning strikes, natural disasters, or short-circuiting, create another form of risk that is difficult to predict.
The term End of Life (EOL) is commonly used to describe the time at which a transformer becomes inoperable. This term is imprecise as it does not convey the actions that can be taken to reduce the risks that most affect a transformer block. These actions could include oil reconditioning and monitoring in the case of accelerated aging or creating redundancy in the system to protect from the abrupt failure of critical assets. A useful term used in this article is the remaining substance (RS), which conveys the concept of a valuable asset that can be consumed or conserved, depending on how the risks are managed. RS was introduced by DTC (Daemisch Transformer Consult company) as a more actionable term instead of relative terms like lifetime or lifespan. It is based on the complete picture taken from the condition assessment resulting from DGA, Furan analysis, oil condition monitoring, and all other available information. It, therefore, is not a simple “index,” rather a concise analysis based on the interaction of indicators, experience, and expertise. The decline in RS is exponential if the appropriate measures are not proactively taken. It is important to institute the remedial and / or conservation measures early enough so RS can be preserved in good operating condition throughout the required operating lifetime of the transformer. Field experience suggests that once RS reaches 60 %, the remaining operating life of the transformer is only six years. By taking proper and timely action to manage risk factors, the transformer’s lifetime can be extended by another 10 to 15 years. The chart in Fig.1, created by the author, depicts the trajectories of RS with and without conservation measures.