Managing transformer lifetime costs with online condition monitoring

The total cost of asset ownership is increasingly an important measure for owners of power transformers. And while operational budgets become tighter, the industry faces a competing need to manage large capital expenditures for new equipment. This puts the onus back on maintenance teams to extend an asset’s useful life, while controlling and preventing unexpected repair and replacement costs that would stretch budgets.

Having a clear and well-planned approach to operations and maintenance (O&M) can help owners of power transformers manage costs properly over the lifetime of their asset. A proper plan should broadly outline its purpose and goals, as well as consider the best approaches to monitoring assets and maintaining them, as there can be significant cost differences between various approaches.

Longer life, lower average costs

To illustrate, while the average lifetime of a power transformer is around 40 years, for individual this can vary by up to +/- 15 years. Though the upfront cost of a transformer represents only part of the total lifetime cost of ownership, which should also include maintenance, repair and replacement. Calculating these across the 55-year lifecycle of a well-maintained transformer as opposed to across a shorten 25 year lifetime can make a significant difference.

Similarly, getting the oil monitoring method right can make significant savings in operational costs. An online monitoring approach to dissolved gas analysis (DGA) collects data on early warning indicators from the transformer oil continuously during the transformer’s operation. This additional data, properly analysed, provides far greater insight into the performance and health of the asset than the limited data that are collected during occasional visits by a technician conducting manual sampling.

With the information from online DGA monitoring teams can identify which transformers are developing faults much earlier and prioritise maintenance for those assets, fitting it into operational windows to minimise costs and reduce revenue losses.

Using continuous data to plan condition-based maintenance not only makes managing resources simpler and cheaper, but can also extend asset lifetimes by allowing operations managers to manage transformer loading until an appropriate maintenance window can be reached. The alternative, a time-based maintenance programme, uses resource to carry out maintenance that may not be needed, and forces assets offline when it is not necessary. (as illustrated in figure 1)

Hidden costs of maintenance

Over the forty -year life time of a transformer online dissolved gas analysis (DGA) monitoring can help manage and extend life. Online technologies offer more insight and greater control over the health and performance of the asset than laboratory testing may do, but not all online monitors are equal and lifetime costs can vary significantly. In particular, some monitoring technologies that have been transplanted from the laboratory, can have highly complex maintenance needs of their own.

Beyond the simple cost of acquiring an online condition monitor, monitors may have ‘hidden costs’. Depending on the technology these could include calibration, the replenishment of consumables and the repair and maintenance of components. Gas chromatography and photo-acoustic spectroscopy in particular, have more quickly wearing components and consumables that need attention. Other non-dispersive infrared-based technologies, OPT100 monitor among them, are designed and built to be maintenance free over their operational lifetimes.  (as illustrated in figure 2)

Balancing probability and consequence

The real cost saving of adopting online monitoring and condition-based maintenance approaches come in the form of the losses that it prevents. While transformers have a low likelihood of catastrophic failure, it’s worth bearing in mind the consequences of such a failure will, for most asset owners, be disproportionately high in comparison to the cost of a simple asset monitoring campaign.

Transformer breakdown can cause interruptions to transmission that have knock on effects up and down the network, as asset owners incur costs for power that goes undelivered, and losses if power is not being produced.

A simple example of how these choices can benefit operational and capital budgets can be illustrate with a Vaisala case study involving a 100MVA transformer. Rapidly-developing insulation damage in this transformer threaten to escalate into a costly unplanned outage. However, using online condition monitoring the team were able to catch the fault early and deal with it at a cost of €55,000. In comparison, the cost of renewing the insulation is estimated at around €150,000. Because the maintenance team are able to identify the fault early and make plans to deal with it, the savings in repair the repairs took only 10 days, instead of a more typical 30. Associated costs savings with this operation include the increased cost of maintenance operations, and a minimisation of operational losses during the time the asset was offline.

When considering transformer maintenance approaches and balancing up its benefits, asset owner’s should take a lifetime costs approach. This should consider all the savings that can be directly attributed to the influence of online condition monitoring technology on maintenance planning and execution.
Read more of Vaisala Online DGA Monitors

Teemu Hanninen
Product Manager