Predictive maintenance: A step change in transformer monitoring

As leading wind energy organisations grow their operational portfolio, they’re also having to focus on developing the electrical infrastructure needed to support the entire generation site. A key asset within an offshore and onshore wind farm is the power transformer which connects the wind energy to the electricity grid. Power transformers have a design life that nominally is at least the typical 25-year life of the wind farm. However, transformers can develop faults well before the end of their life expectancy, leading to failure and ultimately downtime for the wind farm.

Downtime can be extremely costly due to the loss of energy and impact on availability targets. According to an analysis by Business Electricity Prices, if an offshore windfarm with 5.8p/kWh total power capacity suffers one transformer critical failure, this translates to a cost of £508,800 GBP/year, with an onshore wind farm suffering a loss of £402,960 GBP/year. These figures only reflect the loss of energy production and not the cost it would take to repair or replace the transformer that has failed and the fines ensued from missing targets.

Transformers are a single point of failure when connecting wind farms to the electricity grid. Although they are static assets with a relatively simple working principle, they are complex mechanically, made up of several materials, such as copper, iron, solid and liquid insulating materials like paper, wood, porcelain, resin, and oil. Transformers are prone to critical failure due to their complex components.

The biggest concern of ageing and the life expectancy of transformers is the condition of the insulation system, which can be based on organic products. These products are subject to degradation due to usage and eventually they lose the capability to tolerate the stresses a transformer might see in daily use.

Transformer failure can also appear in different ways, depending on the origin of manufacturer and some forms of failure can arise regardless of construction type. These might include tap changer failures, bushing failures, tank failures, moisture ingress, and other forms of dielectric fluid contamination. Sometimes the failure could be purely due to lack of regular maintenance or lack of awareness.

According to a study on the key causes of transformer failure on the Italian grid, one of the main causes of power transformer failure in transmission grids has been ascribed to unpredictable external events, including over-voltages, lightning strikes and through fault currents. The latter ones can be the indirect cause of winding displacement on autotransformers and of electrical failures of transformers interconnecting HV grids. In the case of wind farms, transformers are regularly in remote locations and often at times facing challenging environmental conditions, combining this with the variable nature of wind energy production transformers on these sites are prone to increased stress, caused by continually thermal cycling and harmonic distortion. Due to these conditions, transformers connecting wind farms to the grid can be susceptible to an increased risk of failure when compared to their use on utility installations.

A trial conducted in 2015 by Kelvatek’s transformer experts demonstrated that transformers are repetitively affected by induced mechanical stresses caused by through fault currents that fault recorders do not reveal, and which could critically jeopardise the winding and blocking their system integrity and reliability. It further demonstrates that the Asset Owner is, in most cases, unaware of the electrical and mechanical stresses affecting the transformer, therefore, unable to schedule further investigation and/or corrective maintenance.

Predictive maintenance ensures that a transformer receives the required maintenance before critical failure occurs. This enhanced level of foresight reduces the total time and cost of maintaining equipment by ensuring that only necessary tests are carried out on transformers displaying the relevant risk profile. It also helps minimise downtime and ensures optimal energy production.

With Kelvatek’s TOTUS transformer monitoring solutions, we offer predictive and real-time assessments of the transformers condition to provide Asset Managers with the power to make informed decisions. Our advanced sensor technology combined with the sophisticated data analysis tools and transformer models, give Asset Managers the ability to monitor all key parameters of the asset and provides a complete picture of transformer health in a single integrated solution.

By investing in our cutting-edge transformer monitoring technology, Asset Managers can gain increased visibility and insight into the health and performance of these assets. With this, the wind farm owner or operator gains a better understanding of the potential risks to availability and the consequences to revenue.

Are you interested in finding out more about Asset Monitoring? Get in touch with Kelvatek today to find out more about how we can partner with you to safeguard your supply of wind power to the electricity grid.