Ageing transformers – mitigating risk

Power transformers play an integral role in the operation of the electric power grid. Failures carry not only the risk of extended downtime, but also significantly impact a utility’s finances and reputation. Understanding what the current risks are and how to mitigate them is crucial in maintaining the smooth operation of a power transformer fleet. 

Online monitoring – why now?

Global transformer infrastructure is aging. Designed with an approximate lifespan of 40 years, substation transformers now have an average age of 42 years. Expectations for failures increase proportionally with age and are predicted to peak towards the end of the decade.

While the environmental drive for energy efficiency has helped stabilise overall power demands at a more constant level, electricity is making up a growing proportion of global energy consumption. In addition, rising demand for renewable energy has increased the amount of distributed power generation, which means new challenges for ageing infrastructure.

The modern world is reliant on electricity. The fact that this increased power demand is placed on transformers already operating at their extended lifetime is one of the key challenges facing the industry today. 

Transformer maintenance and monitoring is a topical issue due to technological advancements that have reached the next level. Representing a significant leap forward in what is possible, online monitoring enables real-time feedback on the condition of transformers. This allows the spotting of developing faults as they appear. In particular, multi-gas DGA (Dissolved Gas Analysis) monitors can detect all types of internal faults, even in their early stages. Following gas formation trends in real time can even mean preventing failures.

Detecting faults with online DGA

Initially, faults were fixed as they were discovered. Later maintenance strategies turned into prevention plans. This then evolved into a more holistic approach of condition-based maintenance (CBM), which allows companies to prioritise their service actions, and for budgets to be allocated in the most effective manner. The next step in this evolution is to integrate online monitoring into CBM schemes – an unparalleled way to spot faults developing and stop them in their tracks.

Monitoring devices make it possible to track a variety of key condition indicators. For example, it is possible to have real-time feedback on the dissolved gases in oil; the speed of gas formation can alert an operator to a developing fault. Similarly, it’s possible to record moisture in oil to track potential decrease of dielectric strength. Online monitors eliminate the risk of human errors related to improper oil sampling and handling.

Comprehensive online DGA enables tracking of which gases are being formed. For example, material aging can be detected by the presence of gases created through the degradation of cellulose. DGA can also provide warning signs of thermal faults, partial discharges and overloading when comparing the DGA data to the transformer’s load pattern. Through the types and ratio of gases present, it is possible not only to detect the presence of a fault, but also identify its type. 

Implementing online monitoring

Monitors are used to help in tackling some of the key challenges facing the industry today. With transformer risk levels increasing, monitoring and preventive activities become more important to protect the transformer fleet. This is particularly pertinent when considering personnel trends in the future – fewer staff and increased automation.

Online monitoring offers continuity in the face of personnel changes. While the next decade may see the departure of experienced personnel with personal knowledge of particular transformers, the data collected can provide vital historical context to any new information.

There are several steps to the successful implementation of online monitoring:

• The first is having internal processes in place before the monitors are implemented. The devices themselves will alert faults – but action to halt these can only come from the personnel.

• Finding the right kind of online monitor is crucial. Above all, it must be reliable. It should provide quality data and not raise false alarms and thereby create unnecessary work. Companies need to be able to trust that an alarm will only be raised when there is actual cause for concern.

• Such devices should be simple to set up, so that companies’ own or subcontracted field technicians can install and operate the unit. Similarly, the monitors must be able to handle the harsh environmental conditions they may be exposed to.

Close discussion between the utility company and the monitor supplier is the key to create an effective working solution. Knowledge sharing and harnessing the expertise of both parties to build bespoke solutions is the best way to succeed.

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