Engineers + Chemists = Reliability for Members

Unless you're a chemist or a technician, there's a good chance you've never heard of dissolved gas analysis. Bust as part of our innovative substation maintenance program introduced in 20202, this specialized process has increased reliability and potentially prevented outages to NNEC members, not to mention time in the dark.

“It’s a great tool for increasing reliability,” explains Steve Minor, manager of engineering services. “With this maintenance program, we catch the problem before it occurs.”

NNEC’s substations have over 100 transformers and voltage regulators. Transformers step down the voltage from transmission levels to distribution levels, while voltage regulators have the ability to finely tune the voltage, by raising or lowering it slightly, in response to demand. When our members get home from work in the summer and turn on their air conditioners, demand goes up, and voltage regulators make an adjust­ment to keep the electricity flowing at the right levels to prevent a service interruption. Transformers and voltage regulators are vital, hard-working pieces of equipment that run 24 hours a day. They’re also expensive; each can cost the cooperative anywhere from $5,000 to $750,000 to purchase, maintain, repair, and/or replace.

In the past, NNEC relied on a time-based maintenance program to care for the critical substation equipment. Each piece of equipment got pulled, refurbished, or replaced on a multi-year cycle, regardless of its condition.

“You can’t tell what’s going on from the outside, and there are not always signs that something is wrong until its too late. It’s important to find new ways to diagnose potential problems.”

NNEC’s new substation maintenance program, which combines visual and operating inspections with dissolved gas analysis, allows our crews to get a precise peek into the internal status of transformers and regulators. Chemical analysis of a sample of the cooling oil within each individual piece of equipment can help determine its current “health”, and identify if action should be taken. This is improving equipment lifespan, lowering costs for the cooperative, and improving reliability. Every year, every single critical piece of equipment inside of our more than 20 substations is checked.

“Instead of changing out a perfectly good transformer or regulator every few years, we can use it for the full seven, eight, 10 years, making only minor fixes,” explains NNEC Engineering Technician Gabe Fearing. “We’re getting a better usage over the course of its lifespan.”

In addition to extending the lifespan of some equipment, the program can catch potential problems before there is a critical failure. Without the program in place, crews would not know to intervene before the equipment fails: meaning that outages, potentially affecting hundreds of members, are being prevent­ed each year with this program.

For the Armchair Scientist

Dissolved gas analysis is a deceptively simple procedure, based upon some exceedingly complex chemical reactions. Substation technicians take a sample of the oil from a regulator and send the sample to the lab. The sample is then run through a gas chromatograph. Basically, the oil is burned and the gases released in the process tell analysts about the state of the equipment.

“The ratio of those gas levels to each other tells us what’s going on in the regulator,” Fearing says.

For example, acetylene is created only at temperatures of 700 Celsius or higher. So if there’s a high ratio of acetylene to other gases in the oil sample, that’s a sign that something inside the regulator is getting very, very hot: an indicator that the regulator needs to be replaced, immediately, to prevent outages.

The oil sample is also analyzed with a dielectric test to determine its conductivity. Throughout the lifespan of transformers and regulators, the oil is a coolant and insulator, it helps prevent overheating and conductivity. Unfortunately, the conductivity of the oil, due to the addition of new gasses, increases, reducing the ability of the oil to insulate and regulate the temperature of the unit.

In both cases, the efficiency and effectiveness of the transformers and regulators can be reduced. That inefficiency gets ultimately transferred to line losses: electricity wasted before it gets used, a cost that is absorbed by NNEC and its members.

In this way, decrypting the complex code of gases lets NNEC engineers see when equipment needs to be repaired and adjusted for peak efficiency.

Delivering Power Reliably

“The biggest thing is, by doing this, our substations and their equipment are going to be more efficient throughout our system, and that’s going to translate into more reliability for the membership,” Brad Hicks, president and CEO says. “Because we can find potential issues before they are a real problem, we can reduce the number of outages impacting our system.”

“We serve our members,” Hicks says, “So, we will continue to search for new and innovative ways to improve reliability for our members. It helps the entire membership.”

Higher reliability: now that’s the cooperative difference.