How one electric co-op reduced operations and maintenance costs with versatile DGA monitoring

The client:

KAMO Electric Cooperative, Inc. based in Oklahoma and Missouri. 

Vaisala solution:

A robust combination of the OPT100, MHT410 and Indigo520 allowed this grid operator to ensure suspicious fault gas trending would not lead to an outage.

KAMO Power primarily uses manual sampling and outside labs for dissolved gas and moisture monitoring for its transformer fleet. This process is performed at least once a year, depending on the criticality of the transformer and its DGA history. The breadth of the KAMO territory, however, often requires taking two technicians off regular work to pull samples, not to mention allocating resources for the testing, including aggregating the DGA data results and the interpretation processes.

KAMO wanted to reduce this cost while improving confidence in the interpretation of the DGA monitoring data. This need for actionable insights was especially pronounced for transformers with questionable fault gassing patterns discovered during routine manual lab testing.

In these situations where a potential transformer fault needed to be more closely monitored and the data more carefully analyzed because repair/outage decisions had to be made, KAMO realized that it could use a combination of multi-gas online DGA monitors and single gas and moisture monitors to replace more costly manual sampling.

What follows is the first example of when KAMO integrated these DGA solutions into its standard lab sampling operations, and how it improved operational effectiveness and proved out the concept for further implementation and roll out. This case shows how the integration of fixed and mobile online DGA not only provided more actionable DGA data for better analysis of faults, it does so at a lower net cost, while also reducing the risks to personnel.

Detecting acetylene in an 84 MVA transformer

KAMO has an 84 MVA Waukesha transformer manufactured in 2012 that was installed and energized in September of that same year. This unit was DGA sampled once a year for dissolved gases. In July 2022 the DGA lab results for the transformer showed a concerning gassing trend, as the acetylene content had increased from 0 ppm to 1.2 ppm between the samples taken in July 2021 and July 2022. Up until this point, there had been no acetylene detected in annual DGA lab tests since the transformer had been placed in service. As an immediate response, per the lab recommendations, KAMO maintenance team increased the manual lab sampling frequency to every two weeks. After only a month, with two more samples pulled and tested, the DGA results indicated the acetylene had increased to 3.7 ppm.

Following a consultation with the manufacturer, KAMO ran a series of field tests to determine what could be causing the fault gases to form. Power Factor, Transformer Turns Ratio, Winding Resistance, Insulation Resistance, and Oil Power Factor tests were performed. Also, all of the transformer DETC no-load taps were exercised, the ratios tested and the reactor core ground and main core grounds were resistance tested. No abnormalities were found, but the lab generated DGA results still indicated acetylene was increasing, and had risen to 4.3 ppm.

The decision was made to not remove the unit from service for draining and internal inspection because of the winter weather they were experiencing at the time. Instead, KAMO planned to continue monitoring the unit until next spring, anticipating that the weather would be milder and more suitable for an internal inspection. The maintenance team instituted a monthly sampling routine, even as the concerning acetylene level continued to climb.

Manual sampling costs persist despite an improving gas trend

Regularly sending staff to pull DGA samples for the lab created a lot of administrative work, as well as increased operations and maintenance (O&M) costs. There was also the lurking risk of injury to personnel going out to the site. Yet without another option, the maintenance team continued this manual sampling process. After a few months, in January 2023 the acetylene maxed out to 19 ppm, and then unexpectedly began to drop. The subsequent lab sampling tests showed it was leveling off, but it was hard to determine why.

Luckily during 2023 the acetylene levels continued to settle, and it was decided the manual sampling could be cut back to every other month. By August of 2023, the levels had dropped to 9.7 ppm, which was still high, but trending in the right direction.

The management of this sampling protocol, however, continued to be burdensome and expensive. More troubling was a clear picture of the situation was still not evident to the maintenance managers. Without this confidence, it was believed that continued manual sampling was the only option.

Installing a continuous multi-gas DGA monitor for real-time transformer insights

At this point the maintenance managers decided to install a Vaisala online multi-gas DGA monitor, the Optimus™ OPT100. The goal was to get real-time data on the condition of the unit while it was in operation. As the OPT100 DGA monitor is installed and stays continuously connected, it provides data 24/7 on the fault gassing levels, allowing patterns to become more readily visible and cross referenceable to other factors. Also, with real-time data, the fault severity is easier to evaluate as it shows the gassing trend slope which visualizes the rate of change.

The online monitor was installed in the spring of 2024 to run and assess the transformer during the summer high load period. It took less than a half day to have it installed and running. The robust sensor provided the maintenance team with the confidence to cut back on the O&M manual sampling costs while improving and increasing the amount of transformer gassing data. The key goal was to get more regular gas level information and thereby obtain some insight and confidence in their decisions on what do to do next, including the reduction of manual sampling frequency. With the DGA results provided every hour by the monitor, the maintenance managers had a much clearer picture of the situation and how it changed with loading and temperatures.

The OPT100 revealed to KAMO that the acetylene gassing had settled and even though the transformer was on a higher load for the summer months, by the end of the season the acetylene was down to 6.5 ppm and remaining stable. The team was satisfied with the real-time data, and appreciated it came with no added O&M costs as the OPT100 monitor does not require consumables or scheduled maintenance to operate. Additionally, the measurement information was available remotely, simplifying data acquisition and viewing. Most importantly, however, this data set allowed the maintenance and asset health managers to more closely analyze the gassing situation across a high load operational period and thereby gain the confidence that the fault issue was not an ongoing concern.

The mobile online DGA monitor provided ample data for the KAMO maintenance managers to determine the situation had resolved itself and the transformer could be left in service, with no need to plan for another round of testing, or to move in back up units.

After the mobile OPT100 unit confirmed the condition was stable, the KAMO team installed a Vaisala MHT410 hydrogen gas and moisture monitor. The MHT410 continues to serve as a real-time alarm in case hydrogen starts forming, as this is a key fault indicator gas. In other words, it is one of the first gases to show up when faults begin to develop so it can be used as a “smoke detector” for the development of new faults. It was agreed that this would give sufficient warning if the old issue started to reappear and cause internal deterioration again, or if a new fault developed. This also gave the maintenance managers the confidence to cut the manual sampling down to twice a year, instead of monthly.

Lower operations and maintenance costs through a layered transformer monitoring strategy

This case shows how KAMO was able to achieve better monitoring and more reliable data with the combined use of the mobile multi-gas DGA monitor and the permanently installed single fault gas monitor, while also allowing them to reduce lab sampling to twice a year. By applying each DGA option in a specific time and place, the KAMO maintenance team realized they could better maximize operational efficiency and cut O&M costs. KAMO estimates that it saved tens of thousands of dollars in O&M and testing costs on this one fault case alone, and the savings could have been multiplied if the OPT100 had been commissioned sooner.

As a result, KAMO is now investigating adding fixed DGA monitors and portable units into its maintenance and asset health operations.