​By Chris Lyles

WAPA’s Asset Management and Maintenance teams have recently improved the reliability of the data they receive from dissolved gas analysis. This process is crucial in determining transformer health and can predict failure years in advance, helping WAPA plan its maintenance and capital replacement activities appropriately. 

Improved data means greater efficiency for Maintenance crews, with time and money saved in the process. As such, it’s a great time to discuss how oil testing and dissolved gas analysis assist in determining transformer health, and how the reliability of the resulting data has been improved.

Large and in charge

Large power transformers constitute a significant part of WAPA’s portion of the bulk electric system.  The primary purpose of a power transformer in a transmission system is to transform voltage. For example, voltage may be transformed from 230,000 volts down to 69,000 volts, or from 13,800 volts up to 115,000 volts. 

Transformers take high-voltage electricity with a small current and change it into low-voltage electricity with a large current, or vice versa.  

Having reliable and healthy transformers is a primary goal for any robust, resilient and reliable transmission system. Large power transformers are often difficult to obtain due to their size and are expensive to procure. For context, most of WAPA’s transformers weigh more than 100 tons, range in cost from $1.5 million to $3.5 million and take 18 to 24 months to acquire.  

For these reasons, determining transformer health as accurately as possible is important. 

Blood and oil

Dissolved gas analysis on transformers is similar to the blood tests doctors perform on people. WAPA’s Maintenance crews draw oil samples from transformers and send those samples to a lab for analysis. The lab analyzes these samples to help determine the overall health of the transformer.  

Transformers each contain primary tanks, which house up to 30,000 gallons of mineral oil. The oil’s purpose is to insulate internal electrical components, suppress corona discharge and arcing, and serve as a coolant to draw heat away from the core of the transformer. 

During sampling, a small amount of mineral oil is withdrawn from the transformer and analyzed for dissolved gases, moisture and breakdown of cellulose products.  

The Asset Management team takes these results into account when calculating the health index for each of WAPA’s approximately 400 transformer assets. The calculations are then used by Asset Management and Maintenance to identify the transformers that are most in need of attention.  

This suite of tests performed on the oil samples is commonly called dissolved gas analysis, or DGA testing, and the results provide detailed information about the internal performance of a transformer. DGA testing is one tool WAPA uses to predict potential failure of a unit within the next few years.

Improving the data

Asset Management has recently improved the way DGA test data is entered into Maximo, an application in which health calculations are performed and which stores results for users to reference.  

Prior to this year, maintenance personnel would receive sample results from the offsite contract lab and manually input them into Maximo. This introduced the possibility of human error, which could have a significant impact on the accuracy of health calculations. 

Now, the analyzing lab uploads DGA test results to an online, third-party database accessible by both the lab and WAPA’s asset managers. An asset manager reviews the results, confirms that they are accurate, and “pushes” those results directly into Maximo. 

This improvement allows Maintenance personnel to focus more on their actual maintenance activities and less on data entry. It also provides asset managers with consistent, reliable data to help regions make informed decisions about their maintenance and replacement activities.  

All current and previous test results are now available in Maximo for each of WAPA’s large power transformers.

A process improvement such as this is just one way Asset Management is living up to WAPA’s core value of “be curious, learn more, do better.”

Photo of a transformer

Accurately assessing the health of WAPA’s transformers is crucial to providing reliable power to more than 40 million customers throughout the West (Photo by Chris Lyles). 

Photo of a dissolved gas analysis being performed

​Dissolved gas analysis is performed on oil samples taken from transformers (Photo by Dave Haskin).

Last modified on September 12th, 2023