Sweep Frequency Response Analysis (SFRA) and Transformer Diagnostics M5100 Product Series Doble Engineering Knowledge Is Power SM Apparatus Maintenance and Power Management for Energy Delivery

SFRA Presentation Introduction  This is an S weep F requency R esponse A nalysis presentation:  A tool to investigate mechanical integrity of transformers  When: after relocation, after an incident, or to get a baseline Signal & Reference Leads M5100 Shield Ground Test lead

SFRA Presentation Bushing failure…. This bushing failed catastrophically SFRA showed that the transformer windings were in good shape. The transformer did not need to be scrapped.

SFRA Presentation Bridge Impact Paint scrapes on delivery are suspicious? How did the scrapes get there, and what does the impact recorder say? Do we know if anything moved inside the transformer? SFRA helps you decide...

SFRA Presentation SFRA is really a lot of measurements... Overview Individual measurement made at each frequency of interest to produce a fingerprint Frequency in MHz Some individual resonances

SFRA Presentation If we can measure: changes in the frequency response of a winding caused by winding movement then we can detect winding movement. Overview of test A good repeatable SFRA measurement will detect this problem Bulge in winding caused by electrical fault

SFRA Presentation  Experience: Certain Frequency Bands Indicate Different Problem Conditions Interpretation 400kHz to 2MHz: Movement of main and tap winding leads 2kHz to 20kHz: Bulk Winding Movement Relative to Each Other, clamping structure <2kHz: Core Deformation, Open Circuits, Shorted Turns & Residual Magnetism 20 kHz to 400kHz: Deformation Within the main and tap windings

SFRA Presentation Transformer: Normal Response Three phases respond differently at low frequencies Three normal open circuit responses Results as expected and acceptable

SFRA Presentation One year later Variation is clear indicator of shorted turn on A phase After an incident - one year later... One phase has clear inductive roll off associated with short circuit measurement

SFRA Presentation Null result has value Four results overlaid on this graph from four different years Clearly - the transformer has not changed 1994, 1997, 1999, 2002

SFRA Presentation There are two traces here - suspect phase of suspect unit and same phase of sister transformer Bushing Failure Sister unit has exactly the same shape The two traces are clearly very similar - can just see one trace behind the other No variation between traces implies this phase is OK, despite bushing failure

SFRA Presentation One winding tested twice with each method Method Comparison The impulse responses are ‘roughly’ OK but the huge variability loses the value of the test Two SFRA responses Two impulse responses

SFRA Presentation The VALUE of an SFRA measurement is in the Repeatability: we can avoid false positives and false negatives in decision making The Range and Resolution, from 10 Hz to 2 MHz, and +/- 1dB, means we can make confident diagnoses Used as a decision making tool, SFRA can bring a lot of value in practice 10. Conclusions Decision making with respect to transformers is not an easy job: SFRA helps

SFRA Presentation Thank You. Any questions?

SFRA Presentation Doble’s Application Support  SFRA User Group meets twice a year  On-line User Forum  On-line Client Reference Library  On-line resource center  Telephone application support  Interpretation of all results during first year  Client training

SFRA Presentation Support - User Forum

SFRA Presentation Support - on line results library

SFRA Presentation  Here are some technical questions which informed clients may ask Difficult Technical Questions?

SFRA Presentation  Does your test set guarantee repeatability to +/- 1 dB?  Yes - it means we can trust the results  Does your test set give a resolution of less than 10 Hz below 1 kHz?  Yes - so we can see shorted turns and see the detail in short circuit measurements  Does your test set measure up to 2 MHz?  Yes - so we can see variation caused by tap and winding lead movement Difficult Technical Questions?

SFRA Presentation  Does your test set have an interference band width of less than 1/5 of frequency?  Yes - so we minimize effects of noise at each frequency we measure  Does your test set give a response measured down to -80 dB within 1 dB?  Yes - so we can see details of large HV windings  Does your test set use three leads?  Yes - to remove effects of leads on the measurements Difficult Technical Questions?

SFRA Presentation  Does your test set use coax all the way to the bushing terminals  Yes - so we can remove the effect of incorrect terminations  Do different M5100’s give the same results?  Yes - so we don’t have to use the same test set on each transformer each time  Do results change if you move the test set or rearrange test leads?  No - the results are independent test set location and lead disposition Difficult Technical Questions?