With the increasing cost of fossil fuel and the global demand for alternative energy sources, it is paramount that transmission and distribution (T&D) projects are focused on the end in mind – the absolute lowest total cost of ownership (TOC) with the greatest possible asset utilization.
As projects progress along front-end-loading methodology, the time to start developing your reliability and maintainability plan is in parallel with, or part of, your conceptual design phase.
Simply stated, reliability is related to mean time between failures (MTBF) and maintainability is related to the mean time to repair (MTTR). As your reliability and maintainability plan matures, it should allow for comparison between proposed components for a detailed reliability engineering analysis.
When making selections based on the lowest life cycle costs, you need to understand the failure modes of these components. Look at the probability, severity, detectability of their occurrence (the risk priority number associated with failure mode and effect analysis) and the required control plan to ensure the forecasted availability.
Let’s consider power transformers, which are both costly and critical to the power grid. In determining the specifications for your particular application, is lowest initial cost meeting fit, form and function the only consideration, or is the TCO considered?
With a robust reliability and maintainability plan, things like fault rates and controls are key considerations. Take for example a 5-megavolt-ampere (MVA) transformer with a failure rate which is much lower than that of a 15 MVA transformer.
Determine if the increased number of lower power transformers increases the likelihood of a failure in the data set above than that of the higher power transformer. Use the controls and risk for each as part of the selection criteria.
Criticality also plays an important role in your reliability and maintainability plan. Does the transformer’s criticality justify the high cost of on-line dissolved gas analysis (DGA) to better understand the health of the asset and thus ensure improved utility service?
Fault tracking and root cause analysis also are important factors in ensuring a continuous improvement process. Knowing that the predominant failure mode is insulation breakdown and that transformers in the 300-kilovolt-ampere (kVA) to 10 MVA range have the lowest failure rates are great information when developing specifications for your project.
Although the example used here is a power transformer, the important takeaway is that component selection and the overall T&D system architecture of a capital improvement project can benefit greatly from a reliability and maintainability plan.
This helps to create an asset management strategy that can ultimately help you achieve the greatest asset utilization at the lowest total cost of ownership.
This article first appeared in the October 2008 issue of Utility T&D Magazine.
