Life Extension by Refurbishment of Transformers

Transcription

1 Life Extension by Refurbishment of Transformers C. JAYASENAN by and SHIRISH KANUNGO SIEMENS, India SIEMENS, India 1

2 6th International Conference on Large Power Transformers Modern Trends in CURRENT STATUS OF TRANSFORMER SERVCE Absence of governing standard Closure of some OEMs Improper root cause analysis before refurbishment Repeat of existing design Opt for nearby economic service providers Absence of detailed refurbishment evaluation Modern technological advances rarely used for performance improvement With symptom of early failure, further insights of transformer refurbishment by OEMs is beneficial. 2

3 SUCCESS STORY OF LIFE EXTENSION BY REFURBISHMENT CUSTOMER SPECIFICATION Replacement of failed winding Change voltages (100 to 110kV) Load loss gtd with penalty Many mechanical design improvements Replacement w/o foot print changes (Fans, BR, MOG, SPRR, PRV, OTI, WTI, OFI, Breather, Ladder, Safety railing,cts, Gasket sealing) Replacement of Marshalling box Shot blasting and repainting of tank Repainting of radiators and accessories Rated power Before 90/45/45 MVA After 90/45/45 MVA Ratio (kv) 100/23.1/ /23/11.5 Vector Dyn11yn11 Dyn11yn11 Cooling ODAF ONAF Freq. 50 Hz 50 Hz Phases 3 3 Tapping kV@ 2.5kV steps steps Load loss No data Guaranteed 3

4 CHALLENGES FACED ENGINEERING LL gtd in absence of test data Complicated multilayer wdg with taps at 100kV line end Rare / Complex OCTC schematics & physical connection Reuse of OCTC due to commercial impact. No clue on health of various parts Proper storage, traceability of reused items & disposal of scrap items like windings 4

5 OCTC Schematic OCTC connection 2-pole bridging type rotary switch with Multi-layer winding with taps on 100kV line inter connection end Winding type changed to interleaved disc with regulating winding at middle of 110kV without increase to dielectrics stress with due consideration of step voltage and across tap. 5

6 6th International Conference on Large Power Transformers Modern Trends in CHALLENGES FACED LOGISTICS & MANUFACTURING Transport restriction Additional accessories with minimal change to existing foot print. Tools not suitable for hardware Frequent checks leading to many unplanned action. Sludge removal w/o compromising shop floor cleanliness. DOCUMENTATION Unreadable drawings, absence of dimensions Closure of original manufacturer (YOM : 1960) Modified with minimal records (e.g. No Buchholz relay!) Absence of existing bushings, pumps, fans details 6

7 6th International Conference on Large Power Transformers Modern Trends in REFURBISHMENT ACTIVITIES Joint inspection and scope freezed Re-designed to meet customer spec (ratio, tap steps, loss) Remnant life check of GOES before re-use (though not specified) Re-design evaluated using SIEMENS global engg tool for Electromagnetics Electrostatics 100% dielectrics level - PD free Thermal performance SC withstand (Thermal & Dynamic) Creation of Engg documentation HV winding changed from layer to disc Replacement of windings, insulation, bushings, accessories Re-processing of active part 7

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13 6th International Conference on Large Power Transformers Modern Trends in Information required with refurbishment enquiry Reference Standard (IEC/ANSI / IS) Installation (indoor/outdoor) Rated frequency (Hz) Vector group Rated power (MVA) in different cooling types Rated voltage HV/MV/LV (kv) Voltage regulation (Type, range, steps) Insulation levels on HV / LV / N (U m /AC/LI/SI) Type of insulating oil Rated short circuit duration (s) Loss evaluation (NL/LL/AL ---per/kw) Penalty and Bonus for improvement Impedance u k (%) at rated power, frequency, principal tap position Type of Termination Transport dimensions, weight and mode. Rating & Diagram plate photos Test certificates (Routine/Type tests) Details of cooler (radiator, fans, pumps) Nature of failure, investigation report, conditions before failure 13

14 Customer benefits (Tangible & Intangible) TANGIBLE: Life extended (Proved by test at 100% level PD free!) Up-graded performance (e.g. LL reduced by ~12.5%) Reduced maintenance & Reduced Cooler loss (cooling ODAF -- ONAF). INTANGIBLE: All fabricated parts re-painted after shot blasting to give brand new look Old GOES re-used after proper evaluation (sample test instead of physical examination) Ensured leak proof performance (Gasket design change!) Fresh set of Engg documents. Improved availability of spare parts. No major changes to existing foundation (faster re-installation) 14

15 CONCLUSION Real benefit achieved only with use of latest technology For fair refurbishment evaluation, utilities should consider a) Cost of shot blasting for surface preparation & associated transport cost. b) Cost of sample tests: Material reuse based on sample tests. c) Cost of technology used in refurbishment d) Flexible bidding to allow design improvement during re-design. (To encourage performance improvement instead of mere repeat of existing design) a) Bonus clause for losses in addition to penalty 15

16 THANK YOU!!! 16