Now is the Time

Disruption Risk Drives Transformer Monitoring Changes

By Senja Leivo, Vaisala Corp.

Power transformers are integral in the operation of today’s electric power grid. Failures carry not only the risk of extended downtime, but also significantly impact a company’s finances and reputation. In today’s climate, these risks are more pressing than ever, with a number of influential factors peaking at the same time. Identifying the current risks and understanding how to mitigate them, is crucial in maintaining the smooth operation of power transformers, protecting a company’s fiscal position and safeguarding its reputation.

Online Monitoring-Why Now?

Online monitoring of transformers enables companies to track moisture, temperature and gas levels, and thus eliminates the risk of improper oil sampling. Source: Vaisala

Proper maintenance of power transformers is not a new issue. What is new is the combination of risks facing utility companies, industrial plants, service providers and others for whom transformer performance is a direct concern.

Foremost among these risks is the rising demand for electric power together with an aging infrastructure. While environmental drivers for energy efficiency have helped stabilize overall power demands at a more constant level, electricity is making up a growing proportion of global energy consumption.

According to the U.S. Energy Information Administration (EIA), the proportion of energy delivered in the form of electricity in the U.S. has risen “significantly” in the past six decades. In 1950, it stood at 4 percent; in 2010 it was 29 percent. These figures demonstrate not only that the modern world consumes more electricity, but it’s also becoming more reliant on it for day-to-day living.

Transformer failures, therefore, have greater potential to be disruptive than ever before. The fact that this increased reliance is placed on the shoulders of transformers already operating outside of their extended lifetime is one of the industry’s key challenges-the average age of substation transformers is now 42 years; their designed lifespan is 40 years.

Compounding concern is the fact that investment in new transformers is not currently keeping up with demand. In developed countries, the 1950s, 60s and 70s saw significant investment in power transformer infrastructure. This then dropped off in the 80s, 90s and 2000s. In the U.S., for example, investment peaked in 1974 and reached a low in 1996, according to a presentation from SPX presented at the Electrical Products Group Conference in May 2010. This dearth of investment in recent decades, not just in the U.S. but across the world, is a major contributing factor to driving up the average age of transformers.

Globally, power transformers’ failure rate is typically 0.3 percent per year, which statistically equates to six transformers in a fleet of 2,000. Which transformers will develop faults and eventually fail is impossible to predict without condition-based assessment of every transformer.

This brings us to another pertinent factor as to why transformer maintenance and monitoring is such a topical issue. Technological advancements have brought us to the next era in transformer upkeep-online monitoring. Representing a significant leap forward in what is possible in terms of measurement, online monitoring for the first time enables real-time feedback on transformer condition. This allows the owner to spot developing faults as they appear, discern trends that may indicate declining performance and, crucially, provide the power to prevent failures.

Modern monitoring systems also make it possible to manage the risks presented by the environment. Weather can have a significant impact on power supply, with lightning and hurricanes posing the greatest risk to transformer operation. While the weather may be out of our control, it is possible to monitor conditions more accurately than ever before. Taking advantage of systems that provide early indications of developing storms, their severity, expected path and predicted lightning threats allow companies to stay ahead of unfolding weather risks.

Maintenance, Monitoring, Risk Management and Failure Prevention

The landscape of transformer monitoring and maintenance has evolved in line with emerging technologies and power demand.

Initially, faults were fixed as they were discovered. As world reliance on electric power increased, maintenance strategies turned into prevention plans, with annual oil testing implemented to detect and diagnose developing faults. This eventually evolved into condition-based maintenance, which allows companies to prioritize which transformers require attention most urgently. Based on this information, budgets can then be allocated in the most effective manner.

The next step in this evolution is online monitoring-a more efficient way to identify developing faults and address them early before they become major maintenance issues. Benefits include:

“- Real-time knowledge of the condition of all monitored transformers

“- Early detection of developing faults and associated cost savings in repairs

“- Accurate data to determine conditioned-based maintenance strategies

“- Performance optimization of assets

“- Reliability of data

Through online monitoring, it’s possible to access more data on transformers than ever before-all in real time. Enabling companies to track moisture, temperature and gas levels, online monitoring devices eliminate the risk of improper oil sampling.

Online monitoring devices make it possible to track a variety of key fault indicators. For example, it’s possible to measure online hydrogen levels in transformers, as well as the speed with which hydrogen forms, indicating a potential developing fault. Similarly, it’s possible to record moisture content to track decrease in dielectric strength. Vaisala’s research indicates that when oil’s moisture saturation is below 20 percent, breakdown voltage remains high, but falls significantly when moisture levels increase.

In addition, online monitoring can provide historical data. This empowers companies to spot trends, which again is vital in identifying potential problems and determining the right course of action.

Part of what makes online monitoring so powerful is that it is possible to combine this trend monitoring with the detection of early fault warnings for more effective maintenance through condition-based maintenance strategies.

Identifying trends and having a thorough knowledge of transformer conditions are essential in deploying effective annual condition-based maintenance plans. Accurate, real-time data provides the most up-to-date picture of which transformers need immediate attention and the potential consequences of inaction. The result is a sound basis for making the most cost-effective maintenance decisions.

Implementing an Online Monitoring System

Online monitoring systems are designed to help tackle some of the power industry’s key challenges. From that perspective, they are an exciting development and are likely to move us into a new era of transformer maintenance.

When on the cusp of change, however, a lot of questions always exist. What is the best way to implement an online monitoring system? What will be the return on investment? How can we harness it to reduce transformer repair costs?

These questions still have no concrete answers. As the industry moves into this new era, however, utilities and their vendor partners are working to find them. As more companies adopt online condition monitoring, more assessments on its return on investment will be available. This information will help stop developing faults in their tracks and prevent failures.

This is particularly pertinent when considering current personnel trends. In developed countries, many utilities will see a significant number of existing experienced personnel retire in the next five years. The future picture is one populated by fewer staff and increased automation.

Reduced staff numbers have several implications. Chief among them is that companies must find a way to continue to understand the state of the assets with dwindling human resources. Online monitoring is a solution that can provide much-needed data without the need to invest in more personnel actively engaged in oil sample testing and similar manual operational tasks.

Online monitoring also 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 through online monitoring devices can provide vital historical context to any new information.

These devices also will be a tool with which newer staff can interact-staff whose modern training will be less focused on manual work.

There are several steps to the successful implementation of online monitoring. The first is to understand that internal processes need to be developed in tandem with the implementation of online monitoring devices.

The devices themselves will alert companies to faults, but action to address these faults before they evolve into significant failures can only come from the personnel overseeing the data.

Also crucial is finding the right kind of online monitoring device. Any such system being implemented into a transformer fleet needs several particular attributes.

Above all, it must be reliable. It is not only crucial that it provide good-quality data, but that it does not raise false alarms and thereby create unnecessary work. Companies must be able to trust that an alarm will be raised only when there is actual cause for concern.

Equally important is that such devices are simple to set up, so it is possible that a company’s own field technician can handle the installation. This is vital in ensuring the devices are both accessible and practical. In addition, online monitoring systems must be able to handle a wide range of environmental conditions, from tropical climates to freezing conditions, to ensure that they do not fail when faced with environmental hurdles.

Close cooperation and discussion between the utility company and the supplier is the only way to create an effective working solution. Knowledge sharing and harnessing the expertise of both parties to build custom-made solutions is the best way to succeed.


Senja Leivo is senior industry expert at Vaisala Oyj, Finland. Vaisala is a global leader in environmental and industrial measurement with 80 years of experience in the field. Leivo’s specific focus is on condition-based monitoring of power transformers. She holds a master’s degree in materials engineering from the Tampere University of Technology, Finland.

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