Design Improvement by Diagnostics of Transformers still in Operation and of Apparatuses taken out of Service

Transcription

1 Weidmann-ACTI Inc. Fifth Annual Technical Conference, Albuquerque, Nov 2006 "New Diagnostic Concepts for Better Asset Management" Weidmann-ACTI Inc. Fifth Annual Technical Conference, Albuquerque, Nov 2006; Christoph Krause: Design Improvement by Diagnostics of Transformers still in Operation and of Apparatuses taken out of Service Christoph Krause Weidmann Transformerboard Systems, Switzerland 1 A Member of the Group

2 Contents 1. Power rating enhancement by elimination of the limitation set by induced tank heating through a complex, three-dimensional electromagnetic-thermal study of a transformer still in operation, and subsequent design adaptation. 2. In-depth diagnostics of aged transformers by forensic investigations after having been taken out of service before being scrapped provides accurate information about the cooling efficiency of the apparatus. enables better assessment of the status of similar transformers in the grid 2

3 Contents 1. Power rating enhancement by elimination of the limitation set by induced tank heating through a complex, three-dimensional electromagnetic-thermal study of a transformer still in operation, and subsequent design adaptation. 2. In-depth diagnostics of aged transformers by forensic investigations after having been taken out of service before being scrapped provides accurate information about the cooling efficiency of the apparatus. enables better assessment of the status of similar transformers in the grid 3

4 3D case study: Electromagnetic re-design to 185 MVA 1ph GSU Transformer prevent tank overheating Target: Upgrade MVA-performance by > 20% of name plate rating Problem: Tank flange hot spot = 96 C at 190 MVA The enhanced oil cooling could not cope with the local tank hot spot 4

5 Thermal scan at 190 MVA 5

6 Shorting plate disassembled 185 MVA 1ph GSU Transformer ¾ No Mag Steel Cover Bushing Inspection on site 6

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8 Plane of symmetry Modeling the zone of interest Flux Tangential Boundary Condition Technical challenges: Aluminum shields inside the tank Mild steel tank wall Non-magnetic steel cover parts 3-dimensional modeling 8

9 Creating the FEM mesh: (number of tetraedra) 9

10 Infrared scan 3-D calculation of losses 10

11 Acting together with the manufacturer of the current bus enclosures, a different design was developed with significantly lower losses in the critical area of the tank Original Design Improved Design 11

12 Creating the FEM mesh (number of tetraedra) The mesh was generated using only standard mesh controls, i.e. no special methods were needed. Detail view 12

13 Loss distribution Design Improvements Original Model Modified Model scale: from 0 to 2.5x10 5 W/m 3 Losses in the zone of interest 13

14 3D case study: Electromagnetic re-design to prevent tank overheating Original Design at 190 MVA, tank flange hot spot = 96 C at 228 MVA, tank flange hot spot = 72 C Re-Design 14

15 3D case study: Electromagnetic re-design to prevent tank overheating Summary: Localized tank cover flange heating detected by infrared scan Diagnosis technical challenge: aluminum shields inside the tank, mild steel tank wall, non-magnetic steel cover parts 3D modeling The simulation provided excellent match with the measured tank temperatures The solution consisted in moving the crossover shorting plate to shift flux induced currents from the tank cover flange to the middle of the tank cover Redesigned busbar enclosure permits transformer upgrade from 185 MVA to 228 MVA. 15

16 Other types of simulations / calculations being performed Losses (with/without harmonic currents) and impedance of: Windings (including foil windings and complex circuit arrangements) 3D bus bars arrangements Reactors (with/without core, with/without magnetic shielding) Current distribution in high current windings as occur in industrial applications (arc furnace AC & DC, rectifiers) (3D): Losses in tanks, electromagnetic shields and conductive structures Temperature distribution on tanks (3D) Short circuit: computation of (transient) currents and peak forces on windings Switch-on: computation of transient currents forces on primary winding Electric field studies 16

17 Today, we are performing magneto-thermal calculations regularly local overheating is a problem that occurs frequently. Here another example of such calculation of a GSU transformer. The results are shown on left hand side and the thermal scan is shown on right hand side. 17

18 Reference list ABB Cordoba, Spain ABB Industrial Transformer Legnano, Italy and Bad Honnef, Germany ABB Rectifiers, Turgi, Switzerland ABB Research Center, Baden, Switzerland ABB Varennes, Canada AREVA T&D, Stafford, UK AREVA, Dubai, U.A. Emirates ASA Trafobau GmbH, Bad Arolsen, Germany Crompton Greaves Ltd, Mumbai, India DUBAL, Dubai, U.A. Emirates Dynegy, Houston, TX, USA FRIEM Rectifiers, Segrate, Italy France Transfo, Metz, France Matelec Group, Lebanon Pioneer Transformers Ltd, Canada PII GE, UK Portland GE Company, Oregon, USA STEM Transformers, Trento, Italy Tamini Group, Melegnano, Italy Transpower, New Zealand Wilson Transformer Company, Victoria, Australia (some of our customers) 18

19 Contents 1. Power rating enhancement by elimination of the limitation set by induced tank heating through a complex, three-dimensional electromagnetic-thermal study of a transformer still in operation, and subsequent design adaptation. 2. In-depth diagnostics of aged transformers by forensic investigations after having been taken out of service before being scrapped provides accurate information about the cooling efficiency of the apparatus. enables better assessment of the status of similar transformers in the grid 19

20 Motivation for in-depth diagnostics of aged transformers by forensic investigations: Compare real aging with laboratory accelerated aging experiments (DP, water and acid content, tensile and bending strength, dissipation factor tan δ, resistivity) Verify the cooling performance of the transformer active part Assess the initial DP values of different solid insulation components (when the transformer was put in service) Identify the location of the true hot spot(s) Detect unintended, hot spot areas / design flaws Appraise of the aging condition of similar transformers still in operation 20

21 Equipment and tools Work clothes Work safety 21

22 Equipment and tools Knives Scissors for cutting paper samples 22

23 Equipment and tools Cutting Sawing 23

24 Equipment and tools Pincers of any kind 24

25 Equipment and tools Plastic bags Paper tags Pens (oil and water resistant) 25

26 Equipment and tools Oil container Plastic foil Boxes and crates 26

27 Determination of the aging status by measuring the DP (Degree of Polymerization) of cellulose samples In operation, the cellulose degrades continuously with time This degradation alters (shortens) the cellulose molecules The DP is a good measure of the aging status, because it is proportional to the average length of the cellulose molecules The DP of new Kraft pressboard and -paper is about 1200, that of completely aged (end of life) about 200. DP DP (t) time (years) 27

28 Measurements of the aging status of cellulosic insulation samples taken from three power transformers Transformer A Voltage: 110 / 63 kv Rating: 31.5 MVA Phases: 3 Cooling: ONAF Manufacturer: Siemens Schuckert, Berlin, Germany Operating utility: E.ON, Germany In service: Transformer C Voltage: 380 / 220 kv Rating: 600 MVA / 3 Phases: 1 Cooling: OFAF Manufacturer: MFO, Zurich, Switzerland Operating utility: NOK, Switzerland In service: Transformer B Voltage: 220 / 110 kv Rating: 140 MVA Phases: 3 Cooling: OFAF Manufacturer: TRO, Berlin, Germany Operating utility: Vattenfall, Germany In service: one phase region of sample taking (top to bottom along axial height) 28

29 Transformer A Voltage: 110 / 63 kv Rating: 31.5 MVA Phases: 3 Cooling: ONAF Manufacturer: Siemens Schuckert, Berlin, Germany Operating utility: E.ON, Germany In service:

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31 Transformer A Voltage: 110 / 63 kv Rating: 31.5 MVA Phases: 3 Cooling: ONAF Manufacturer: Siemens Schuckert, Berlin, Germany Operating utility: E.ON, Germany In service: Core LV HV Tap > < 200 Degree of Polymerization LV HV Tap bottom middle top Windings 0 31

32 Transformer B Voltage: 220 / 110 kv Rating: 140 MVA Phases: 3 Cooling: OFAF Manufacturer: TRO, Berlin, Germany Operating utility: Vattenfall, Germany In service:

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34 Degree of Polymerization Transformer B Voltage: 220 / 110 kv Rating: 140 MVA Phases: 3 Cooling: OFAF Manufacturer: TRO, Berlin, Germany Operating utility: Vattenfall, Germany In service: LV HV Tap 0 bottom middle top Core Tert LV HV Tap DP > < 200 Windings 34

35 Transformer C Voltage: 380 / 220 kv Rating: 600 MVA / 3 Phases: 1 Cooling: OFAF Manufacturer: MFO, Zurich, Switzerland Operating utility: NOK, Switzerland In service:

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37 Transformer C 1200 cylinders Voltage: 380 / 220 kv Rating: 600 MVA / 3 Phases: 1 Cooling: OFAF Manufacturer: MFO, Zurich, Switzerland Operating utility: NOK, Switzerland In service: laminated strips Core Tertiary LV HV DP > < 200 Degree of Polymerization Tertiary LV HV bottom middle top Windings 0 37

38 Frequency B C A Degree of Polymerization 38

39 Influence of water on the ageing rate Degree of Polymerization % water content <0.5% water content 40 C 50 C 60 C 70 C 90 C 80 C Degree of polymerization C C C C 0 60 C 70 C Aging time (years) Aging time (years) Aging kinetic equation: Due to the moisture increase during transformer life, the determination EA of the operational temperature, 1 at different locations in the transformer, = A e R T is not precise. t DP(t) 1 DP 0 39

40 Summary The DP profiles matched the expectation: lower DP-values at the winding top and around the conductors, higher values at the bottom and of the inter-winding insulation. The insulation of transformers A (50 years) and C (40 years) was still in relatively good condition. The youngest transformer B (30 years) had reached its end of life - continuing operation would have been associated with catastrophic failure hazard. The moisture content was high, perhaps right from the beginning? The DP of paper at the beginning of life time was lower, due to overheating during drying? The cooling design was insufficient? The transformer was operated beyond name plate? 40

41 Remarks It takes relatively little effort to collect solid insulation samples, when power transformers are scrapped. The findings may be of high value. For a comprehensive aging replica, it is necessary to take samples systematically throughout the transformer. With the water content information of the samples, it is possible to assess the operating insulation temperatures with better precision. Yet, measuring the moisture of the samples requires quick handling on-site, due to inevitable water absorption when exposed to the (humid) air. 41

42 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents 42

43 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents Plan (sequence of dismantling): winding, top to bottom, radial orientation, inter-winding insulation, different phases 43

44 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents Plan (sequence of dismantling): winding, top to bottom, radial orientation, inter-winding insulation, different phases Assigned responsibilities on site: who is doing what Experts shall take the samples 44

45 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents Plan (sequence of dismantling): winding, top to bottom, radial orientation, inter-winding insulation, different phases Assigned responsibilities on site: who is doing what Experts shall take the samples (local) Work safety instruction and strict adherence to 45

46 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents Plan (sequence of dismantling): winding, top to bottom, radial orientation, inter-winding insulation, different phases Assigned responsibilities on site: who is doing what Experts shall take the samples (local) Work safety instruction and strict adherence to Time (patience). Envision unforeseen difficulties and effects. Teamwork! 46

47 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents Plan (sequence of dismantling): winding, top to bottom, radial orientation, inter-winding insulation, different phases Assigned responsibilities on site: who is doing what Experts shall take the samples (local) Work safety instruction and strict adherence to Time (patience). Envision unforeseen difficulties and effects. Teamwork! Transformer operation records: temperatures, oil moisture, maintenance (oil reclaiming etc.), power flow Co-operate with transformer manufacturer - difficulty: old apparatuses Respect (local) working hours (unions!) 47

48 Preconditions for valuable forensic analysis of power transformers Acceptance of project and orientation of the transformer scrapping staff, surplus time is about 1 day Transformer drawings for determination of sampling; transformer design & calculation documents Plan (sequence of dismantling): winding, top to bottom, radial orientation, inter-winding insulation, different phases Assigned responsibilities on site: who is doing what Experts shall take the samples (local) Work safety instruction and strict adherence to Time (patience). Envision unforeseen difficulties and effects. Teamwork! Transformer operation records: temperatures, oil moisture, maintenance (oil reclaiming etc.), power flow Co-operate with transformer manufacturer - difficulty: old apparatuses Respect (local) working hours (unions!) 48

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