Guest Article
Four Common Mistakes in Sweep Frequency Response Analysis Testing
Gu e st A r ticle
Jeff Ward, Solutions Director at Doble Engineering Company
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Sweep Frequency Response Analysis (SFRA) testing provides insight into the mechanical and electrical integrity of transformers, reactors, and other equipment with windings. An SFRA instrument sends a signal into the transformer winding at a number of discrete frequencies and measures the returning signals. Damage, physical changes, and electrical changes can be detected by inspection of the graphical results or by comparing them with results from previous test sessions or from testing of similar apparatus. When set up and used properly, SFRA testing is a powerful tool - for baseline testing of a new transformer in the factory, as part of routine diagnostic testing, or after a system fault. SFRA tests are particularly dependent upon consistent test setup for each test session in order to provide accurate and reliable results. Incorrect setup can create variations that may mask changes in a transformer or create a false positive.
Avoid these common mistakes and save time on return trips for additional testing:
1. Poor Grounding Poor grounding practices can have a significant impact on test results. The grounding of the transformer is important, as is the entire signal ground path of the measurement setup. When the grounding path introduces additional impedances due to poor connections, the signal is measured with a different reference, causing changes to the traces – from subtle to extreme. For the best outcomes, ensure all safety and measurement grounds are solid! 2. Poor Test Lead Connections Test leads that are poorly connected to bushing terminals introduce extra impedances into the measurement circuit. These impedance changes impact a wide range of frequencies and will yield poor comparison to prior test results made with good lead connections. SFRA measurements are made at a relatively low voltage. A little extra effort to ensure a clean surface for the measurement lead connections can be critical to getting good results! 3. Inconsistent Tap Changer Positioning When tap changers change position (either on-load tap changers or
ELECTRICAL MIR ROR
|| September 2021 ||
Jeff Ward is a Solution Director at Doble Engineering Company, with a focus on off-line diagnostics. Jeff’s portfolio of Circuit Breaker and SFRA test solutions expanded in 2017 to include the entire Vanguard Instruments product line after Vanguard became a Doble brand. As a Solution Director, he acts as a focal point within the Doble and customer communities, working to satisfy the end-user’s requirements with existing Doble offerings, and by establishing the roadmap for ongoing development of products and services. Jeff has more than thirty years of experience in technology work, starting in the U.S. Air Force maintaining secure communication systems, followed by work at several major defense contractors developing intelligence and communications systems. Jeff’s commercial work has included developing network security products at several startups, and he worked previously at Doble as part of the TDR9000 development team. Prior to rejoining Doble in 2009, he was a Senior Member of Technical Staff at General Dynamics Mission Systems. Before taking on his current role at Doble, Jeff was a Project Manager in Doble’s R & D Engineering group. He holds a Bachelor of Science degree in Electrical Engineering Technology from Northeastern University and a Certificate in Project Management from Villanova University. Jeff is a certificated Private Pilot, but limits his aerobatic maneuvers to his fleet of radio-controlled model aircraft. ||www.electricalmirror.net||
