Transformer Diagnostics | Sweep Frequency Response Analysis
- 1. Transformer Diagnostics SWEEP FREQUENCY RESPONSE ANALYSIS
- 2. Transformer – An Insight
- 3. Transformer – Winding Structure
- 4. Transformer Failure Modes 36% Mechanical 37%… 6% Environmental 5% Maintenance 16% Unknown Failure Modes Mechanical Electrical Environmental Maintenance Unknown CIGRE
- 5. Mechanical Failure Mechanism Transformers under fault or excessive overload conditions
- 6. Mechanical Failure Mechanism Large electromagnetic forces on windings during fault conditions or overloads can cause windings to move and even permanent winding and core deformation • This may result in insulation damage. • Turn to turn faults are the most likely • Insulation damage usually results in a failure of the transformer which is uneconomical to repair
- 7. Mechanical Failure Mechanism CAUSE: • Electromagnetic Forces due to high current flow (FαI2) • Mechanical shocks during transportation or relocation of the unit EFFECT: • Insulation damage – Uneconomical to repair • Compressive Failure of Winding (Hoop Buckling) • Spiral tightening – De-rates fault duty • Coil clamping failure • End insulation collapse
- 8. Transformer - Design Issues Transformers should be designed to withstand through-faults in accordance with AS-60076-5 However, transformer OEMs rarely short-circuit test the units because of the costs involved. Section 10 of AS-60076-1 classifies short-circuit test under the “Special Tests” category. Unfortunately, it is not mandatory for manufacturer's to carry out “Special Tests”, unless, specifically requested by the customer. As a result the fault duty of many transformers often remain unchecked. A high ratio of new transformers fail short circuit tests, so the short-circuit strength of transformer designs must be verified. X
- 9. Transformer – Failure Transformer failed several years after closing on a fault
- 10. Detection Problems Dissolved Gas Analysis Dissolved Gas Analysis will only indicate a problem when the insulation has been damaged (Usually too late to repair). Internal Inspections Internal visual inspections are often inconclusive and require transformers to be transported offsite. (Costly downtime) Electrical Tests Winding failures can usually be diagnosed by various electrical tests such as TTR, Power Factor etc… (But not always).
- 11. Mechanical Faults Mechanical faults are much harder to detect Transformers may be critically damaged without the asset owner being aware of it!
- 12. What is SFRA A Tool that detects Mechanical Distortions in Power Transformers If undetected, the mechanical fault will manifest itself into an electrical fault (dielectric or thermal) which would result in the loss of transformer. Hence periodical testing is recommended for all critical units What are these distortions? Movements in the Core Movements in the HV/LV Windings Release of clamping pressure Why do mechanical distortions occur? Due to a fault Due to an overload During Shipping and/or Relocation
- 13. Fundamentals of SFRA Transformers are complex RLC circuits L & C components have a strong geometric dependence Physical damage results in changes of the RLC network This is precisely what we are looking for! These changes are measured by using SFRA
- 14. SFRA Working How does it work ? A low voltage (10V p-p) signal with varying frequency (10Hz to 2MHz) is injected into the transformer. Both the input and the output signals are measured. The ratio of the two signal gives the frequency response of the transformer. This ratio is called the transfer function from which a change in the geometry of the transformer components can be established.
- 15. Frequency Response of RLC Elements 0 100 200 300 400 0.1 1 10 100 Resistance ( R ) Capacitance ( C ) Inductance ( L )
- 16. Typical Transformer WYE Winding (HV)
- 17. Typical Transformer DELTA Winding (HV)
- 18. Transformer Damage Indication Other phases identical A-Phase bad
- 19. Interpretation through Experience Less than 2 kHz Band Core Deformation, Open Circuits, Shorted Turns & Residual Magnetism 2 kHz to 20 kHz Band Bulk Winding Movement Relative to Each Other, clamping structure 20 kHz to 200 kHz Band Deformation Within the main and tap windings 200 kHz to 2 MHz Band Movement of main and tap winding Leads Certain Frequency Bands Indicate Different Problems
- 20. Case Study SFRA test conducted onsite Results indicated issues with the symmetry of - A and C phase Two phases have shifted to a lower resonating frequency
- 21. Case Study Transformer sent offsite for internal inspection Detanked
- 22. Case Study Clear bulge in winding Inspection of bad transformer revealed hoop buckling on A and C phase LV windings
- 23. Case Study What was found ? Buckling on Damaged Phase
- 24. Conclusion SFRA results are one of the most important tools in making Operational & Financial decisions Data supplied helps with decision making Decisions include: Ranking assets for replacement Justifying mid-life refurbishment Purchase of spare Decision making with respect to transformers is not an easy job SFRA makes it easier for you to make informed decisions at the right time, that would add value to your business
- 25. Companies Harnessing the Benefits of SFRA
- 26. At Integral Power, we can help you understand the true condition of you transformers, helping you make the right decision, every time! Contact us today to learn more !
- 27. Thank You tlF y g vs Follow us: W W W.INTEGR A LPOWER .COM. AU PO Box 1070 Narellan, NSW 2567 Phone: 1300 206 964E info@Iintegralpower.com.au