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Watching and Waiting: A Blueprint for Transformer Maintenance

How online monitoring can prevent costly failures.

Fortnightly Magazine - July 2006

Serveron’s latest system, the Transformer Monitor Model TM8, works with the new standard to measure the presence of numerous gases that may indicate an impending problem.

“[The new standard] enables [utilities] to stretch their limited capital expenditure, operation, and maintenance budgets while preventing avoidable power outages and their attendant problems,” Tichelman says. Serveron says the constant monitoring of these transformers—which range in price from $1 million to $6 million (and sometimes more)—reveals whether utilities need to shut down, repair, or replace the transformers.

Water Worries

Catastrophic transformer failure is exactly what Lewis Shaw seeks to avoid. Shaw’s choice for Brunswick EMC, an electric co-op in North Carolina, is GE Energy’s Hydran monitoring device, which continuously monitors transformer insulating fluid, dissolved gases, and moisture. “A catastrophic failure would be a nightmare,” says Shaw, manager of engineering at the co-op. “The collateral costs of clean-up and repair are just so prohibitive. Not to mention the cost of transformer replacement.”

More than 20,000 of the company’s Hydran monitoring units are installed worldwide, continuously measuring hydrogen, carbon monoxide, and other key fault gases. Hydro-Quebec has one of the biggest installed bases of the units, while Manitoba Hydro was one of the earliest adopters of the technology. “Some of the largest utilities in the United States also were early adopters, and continue to use this technology,” says Brian Sparling, principal application specialist at GE Energy.

“Normally, these are very reliable machines,” Sparling says. “Some of them last 40 or 50 years. They’re still in service. The failure rate is about 1 to 2 percent per year, so 98 percent of the time, the transformer is behaving normally. But failures are random in nature. You cannot predict when something is going to go wrong. The virtue of our device is you can remotely communicate with it. The engineers can observe how quickly the gases are increasing in real time. That’s the benefit of continuous monitoring.”

The Hydran M2, introduced in the fall of 2003, added the ability to measure moisture and other critical signals to the Hydran line. If the transformer is wet, the Hydran M2 takes the various sensory inputs and computes the information, alerting the maintenance engineers that the unit needs to be dried out.

“Moisture inside the tank is the worst enemy of the transformer,” Sparling says. “Oil only holds 1 percent of the total water inside the tank. Ninety-nine percent of the moisture is held inside the solid insulation, which is essentially paper. That’s the killer of the transformer. If that gets excessively wet, the aging rate [of the transformer] increases exponentially, so your transformer isn’t going to ‘live’ as long. It also can lead to something no dissolved combustible gas detector will pick up: ‘bubbling,’ where moisture bubbles off the vapor insulation on the conductors of the transformer. That will lead to an immediate failure.”

Backed by Capital

Although the new Serveron standard is voluntary, it’s already being implemented at Arizona Public Service (APS). “[The new standard] gives us better transformer condition knowledge than previous methods, and the technology and software are reliable,”