The purpose of acoustic emissions testing is to detect problems that might develop before the regular, scheduled annual maintenance and to avoid a failure or detect problems well in advance “before they get out of control,” according to Jay Garnett, substation maintenance engineer at National Grid USA.

National Grid wants to show other utilities that there are ways to be proactive before you have a failure, and acoustic emissions diagnostics is one way to do that.

“Reliability is very big with the utility business—being a large provider, we want to make sure that we have a reliable system, and that if we have a problem, we can service it before it fails,” Garnett said.

The AE diagnostic technique is a non-intrusive in-service test used for monitoring acoustic signals produced by partial discharge and loose components. It captures and processes AE signals primarily in the ultrasonic domain. Characteristics are extracted from the measured AE signals. This information is used to determine the nature of the AE source, which can be matched to various incipient faults within tank circuit breakers.

National Grid and Doble Engineering participated in a collective study of SF₆ filled dead tank circuit breaker diagnostics using the AE diagnostic technique, and they are presenting their experiences at the Finepoint Circuit Breaker Test and Maintenance Training Conference in October.

Garnett will be speaking with Charles Sweetser, product manager for the SFRA and Circuit Breaker Test products at Doble Engineering.

According to Garnett, National Grid experienced a failure of an ABB PME 362-50-30 SF6 filled dead tank circuit breaker on April 4, 2005, at its New Scotland substation in the Albany, New York, area. The failure occurred on Phase A, which had approximately 3200 operations on it. This particular unit is used to switch 345 kV, 135 MVAR capacitor bank. According to digital fault recorder analysis, the pole opened but then arced across the interrupter with it, finally faulting in a phase-to-ground fault. In response to the failure, this unit was identified as a good candidate for AE testing.

Now, National Grid is implementing AE by introducing the Doble DFA100 into its maintenance program.

Sweetser said that AE can definitely expand diagnostic ability. “The user is ultimately responsible for determining the necessary requirements for field test and maintenance justification of SF6 filled dead tank circuit breakers. Assessing the condition of dead tank breakers is often difficult. Diagnostic testing is considered limited for dead tank breaker technology,” he said. AE helps to identify and locate incipient failure modes, such as PD, particles, and mechanical defects.

The presentation will provide a detailed investigation including in-service AE testing and teardown associated with an ABB PME 362-50-30 SF₆ filled dead tank circuit breaker. This investigation was performed in reaction to the New Scotland failure. The presentation will show that the two remaining poles associated with this unit were exhibiting a similar incipient failure mode that can be traced back to the original failed pole.

“They’ll know what to look for when you go inside one of these–what partial discharge looks like inside of a breaker, some of the mechanical problems that you can have with a breaker,” Garnett said.

The presentation will include several photos, along with charts from the software “so you can see the patterns of the different types of particle discharges, the mechanical particles flying around, or electrical discharges going on. They all have different signatures,” Garnett said.

The end user will have a better understanding for applying the following to SF6 filled dead tank circuit breakers after this session.

Jay Garnett has worked in the utility industry for over 24 years and has experience in substations, hydroelectric, geothermal, fossil fuel, and nuclear generation construction, maintenance, and testing. He worked for Pacific Gas and Electric from 1983 until 1992 when he moved to the East coast to work with Niagara Mohawk which is now National Grid.

Garnett has completed six years of apprenticeships, holding certificates as a journeymen electrician and a journeymen electrical technician. He also was a supervisor for substation crews, and then supervising relay technicians for five years before joining the O&M Services group in February of 2007. Jay is a member of IEEE and is the current vice-chairman of the Doble Engineering Bushings, Insulators, and Instrument Transformers Committee.

Charles Sweetser received a B.S. of Electrical Engineering in 1992 and a M.S. of Electrical Engineering in 1996 from the University of Maine. He joined Doble Engineering Co., Watertown, Massachusetts, in 1996, where he presently holds the position of Product Manager for the SFRA and Circuit Breaker Test (TDR) products, which includes research and development of new products and applications. While at Doble Engineering Company, he has published several technical papers for IEEE and the Doble Client Committees. As a member of the IEEE Power Engineering Society (PES) for 14 years, he actively participates in the IEEE Transformer Committee, and presently holds the position of Chair of the FRA Working Group PC57.149.