By Randy Schrieber, North America Region Manager, Service Marketing & Sales for ABB's Power Products Division
Electric utilities across the country are being squeezed by similar situations to the one at Minerva Power & Light. Jim should prioritize maintenance activities by taking a systematic approach that analyzes the status of Minerva’s fleet of power transformers. By performing a quantified risk assessment, the utility can focus its maintenance dollars and people on units with a higher risk of failure. A broad-brush approach to service resource allocation wastes money by over-servicing good equipment and neglecting assets that have a high potential of failure. Understanding the difference is the key.
Large power transformers have many potential causes of failure. Such failures are often triggered by the cumulative result of loading, system disturbances and the environment. A general assessment of potential failure based solely upon equipment age is too simplistic. Risks of failure can be categorized into four areas.
- Mechanical. It is fairly common for a transformer to fail due to a through-fault. Each unit needs to be evaluated for the risk of a short circuit. Risk factors include transformer design, dielectric and thermal condition of the windings, reclosing practices and the average number of through faults in a given year.
- Thermal. An aged transformer with brittle insulation and loose windings is more likely to fail. Risk factors include temperature, age of the transformer insulation, load profile and MVA size.
- Electric. Dielectric failures can be caused by both equipment design and condition. Design knowledge and historical information are important, as well as diagnostic data, such as the amount and types of dissolved gasses in oil.
- Accessory failure. This includes risks of the operational breakdown of an accessory, such as coolers, load tap changers, bushings and controls.
ABB uses over 60 factors to calculate the risk of transformer failure for maintaining a power grid. Similar analyses can prioritize maintenance on other equipment, such as HV breakers and LV and MV switchgear. Such assessments improve the ability to identify the most critical conditions and highlight the maintenance tasks required to reduce that risk. The end result is fewer service disruptions and lower overall maintenance costs.
Randy is North America Region Manager, Service Marketing & Sales for ABB's Power Products Division. His responsibilities include asset assessment, upgrades and life extension as well as repair and maintenance for switchgear, protection and control, HV breakers and power transformers.
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