By Tony McGrail, Doble Engineering Co.
There is no denying that electric utilities and owners of large transformers have more data at their fingertips than ever before. This can be both a blessing and a curse: More data should bring clarity, but it also can bring confusion.
Condition monitoring can supply more data more frequently to support asset condition decisions. The reality is that all assets will eventually fail, and deteriorating condition is a major contributor to an increasing likelihood of failure. That doesn’t mean, however, that a utility shouldn’t do everything it can to manage the health of its assets. Well-done condition monitoring is key to a holistic view of asset health, and can immediately alert the transformer owner of an important condition change.
Planning, strategic thinking and cross-functional collaboration are required to avoid confusion and gain value from condition monitoring programs. Following are four questions that should be answered before implementing a condition monitoring program:
1. How do I know condition monitoring is right for my organization?
Condition monitoring platforms are on-line systems that can yield real-time information to support up-to-the-minute decisions and long-term asset replacement plans. For many years, asset owners have relied on scheduled testing, maintenance and inspections to obtain asset condition data to support decisions. System constraints have made outages more difficult to plan, however, and the ability to perform conventional testing to generate condition data has been reduced, making it difficult to obtain even barely adequate data for justifiable and reliable decisions.
The reality is that asset conditions can change more rapidly than scheduled off-line testing can identify, leaving organizations vulnerable to costly damages and potential outages. Having information delivered in real time gives asset owners the power to target their intervention activities, reduce operating and maintenance costs, avoid preventable failures and reduce business interruptions costs. Condition monitoring targets known and identifiable deterioration mechanisms, so when choosing a monitoring system, it’s important to take the following steps:
“- Identify likely failure modes. Understand the state of the assets, where vulnerabilities exist and what will most likely result in a failure mode.
“- Know what to look for. Identify symptoms that result from the failure mode and measure parameters which relate to them.
“- Pick a sensor: Use a sensor that can respond to changes in the measured parameter in a reasonable amount of time to allow preventative action to take place.
Condition monitoring is a powerful tool that can provide great value, but no monitor will detect every failure mode because they are not universal and failures may come from external causes. For example, condition monitoring cannot identify weather-related issues or animal incursion problems-unless they lead to a degree of deterioration rather than complete failure.
Overall, it’s important to understand that applying condition monitoring does not remove the need for someone in the organization to understand the data and the implications for the asset. Someone must know what’s going on and how to fix it.
2. What problem are we trying to solve?
This is by far the most important question organizations need to discuss prior to applying condition monitoring. Condition monitoring platforms are flexible and robust tools, but organizations need to have a clear plan and goals for what they hope to achieve with the platform for it to be a success. If an organization has not identified the appropriate symptoms to monitor, it is quite possible for a monitoring system to “miss” a failure. Other common issues that occur from skipping this step are an inadequate frequency of measurements and “limits” for alerts and alarms that are too loose.
Power transformers can fail due to a variety of dielectric, thermal and mechanical causes, making it hard to predict what will cause trouble in your own transformers. If there are particular issues with a transformer, such as overheating due to a winding hotspot, or a deteriorated bushing from a particular manufacturer, targeted condition monitoring could be needed. If you are looking to monitor the overall health of a transformer, general condition monitoring, including dissolved gas analysis (DGA) and temperatures, may be sufficient. This won’t detect all potential problems, however, and a risk that certain failure modes can occur without warning still exists. For more comprehensive monitoring, bushing “True Power Factor”/Tan-Delta data, operational (SCADA) data, partial discharge (PD) data, DGA and a means to correlate all data to mine for anomalies and indications of a failure mode in operation will be needed.
3.What should you look for in a solution?
The condition monitoring platform should be able to gather and analyze data from an individual asset or several assets across multiple stations. The benefit of using a condition monitoring platform is that it provides a single point of access to data from all data sources. In addition, it allows for interrogation of root data and derived values both locally and remotely using a simple interface. It also increases the availability and use of monitoring data within an organization.
Two additional characteristics to look for in a condition monitoring platform are flexibility and scalability. You might want to monitor one measurement parameter, such as bushing leakage currents, on one transformer at a station, but down the road you might need a comprehensive view of all transformers at that particular station. Preparing now for future needs will save time, money and headaches down the road.
4. What is your response plan?
Hooking up monitors for DGA, PD and temperature is important, but without a response plan strategy in place, they can actually cause more chaos than good. Clear processes and plans for how to respond to every possible alert, alarm and notification must be in place. That plan should go beyond purely engineering response or asset management response and also coordinate with operations and system management.
In addition, a clear plan for response and communication chain should be in place so that everyone is on the same page regarding who is best equipped to review alerts and information that comes from the condition monitoring platform. Creating this sort of plan provides the team with a plan of action and allows swift, smart actions. Imagine that through a condition monitoring program an alert comes in for a bushing leakage current, and according to the limits set by your plan this is a high-level alert. A successful response would involve the system operators switching out the transmission class transformer within two minutes-following a pre-agreed plan without further question or discussion. This exact scenario is a true story, and ultimately saved at least two transformers from failure.
Condition monitoring is a great tool to support asset decisions, and when applied with care has demonstrated ability to detect failure modes and avoid failures. Organizations that apply condition monitoring successfully have thought through their business cases, identified cost benefits and applied condition monitoring to target known failure modes, thus reducing the likelihood or reality of failures. Ultimately, condition monitoring allows you to plan responses to changes in condition and quickly act on that plan when the time comes.
As solutions director of asset management and monitoring technology for Doble Engineering Co., Tony McGrail provides condition, criticality and risk analysis for utility companies. Previously Tony spent over 10 years with National Grid in the UK and the U.S. He has been both a substation equipment specialist, with a focus on power transformers, circuit breakers and integrated condition monitoring, and has also taken on the role of substation asset manager and distribution asset manager, identifying risks and opportunities for investment in an ageing infrastructure. McGrail is a Fellow of the IET, a member of the IEEE and the IAM, is currently chair of the Doble Client Committee on Asset and Maintenance Management and a contributor to SFRA and other standards at IEEE, IEC and CIGRE. He holds a bachelor’s degree in physics, master’s and doctorate degrees in electrical engineering and an MBA. McGrail is an adjunct professor at Worcester Polytechnic Institute (Massachusetts), where he teaches power systems analysis.