THE OLTC AS AN "OIL ISOLATED SYSTEM" IN THE TRANSFORMER & OIL ANALYSIS IN OLTC. I Hr. Dr. Hurm, Hr. Dr. Schübel I I

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1 THE OLTC AS AN "OIL ISOLATED SYSTEM" IN THE TRANSFORMER & OIL ANALYSIS IN OLTC MR Hr. Dr. Hurm, MESSKO Hr. Dr. Schübel Seite 1 von 39

2 Table of contents Part 1: 1. Introduction: working principle of an OLTC 2. Differences between OILTAP and VACUTAP OLTCs 3. The insulating oil as a key design parameter for OLTCs 4. Future development: Common Oil compartment? 5. Summary Seite 2 von 39

3 Table of contents Part 1: 1. Introduction: working principle of an OLTC 2. Differences between OILTAP and VACUTAP OLTCs 3. The insulating oil as a key design parameter for OLTCs 4. Future development: Common Oil compartment? 5. Summary Seite 3 von 39

4 Tap-changer U1 Kern core U2 Function of a regulating transformer: The voltage regulation in a power transformer will be achieved by changing the ratio of the transformer by adding turns to or subtracting turns from either the primary or the secondary winding U1 n1 = U2 n2 n1+n2 n2 Therefore, the transformer is equipped with a so called regulating or tap winding. The selection of the taps is carried out with a tap-changer. tap winding U1 n1+ n2 = U2 n2 different ratio Seite 4 von 39

secondary winding U1 n1 = U2 n2 n1+n2 n2 Therefore, the transformer is equipped with a so called regulating or tap

5 An On-load Tap-changer typically consist of some different components diverter switch own oil compartment: function: switching from one tap selector level to another tap selector level. pre-selector (optional) transformer oil: function: e.g. reverse switch reversing the polarity of the regulating winding to duplicate the regulating range tap selector transformer oil: function: connecting the different taps of the regulating winding to the diverter switch; preselecting the next tap postion. Seite 5 von 39

reverse switch reversing the polarity of the regulating winding to duplicate the regulating range tap selector transformer oil:

6 Ideal ratio between transformer coil winding and OLTCs Seite 6 von 39

7 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa I L R R TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 7 von 39

8 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa I L R R TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 8 von 39

9 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa I L R R TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 9 von 39

10 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa I L R R TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 10 von 39

11 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 Ic MCa MSCa I L 2 R R I L 2 TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 11 von 39

12 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa R R I L TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 12 von 39

13 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa R R I L TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 13 von 39

14 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa R R I L TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 14 von 39

15 Function of a diverter switch: from tap position n to n+1 tap n tap n+1 MCa MSCa R R I L TCa1 TCb1 MSCb MCb n approx. 60 ms n+1 MCa MSCa TCa1 TCb1 MSCb MCb Seite 15 von 39

16 Important: OLTC switching sequence (open-close of different contacts) must remain widely constant: - independent of the type of insulating oil - independent of the oil temperature (within specified range) MCa MSCa TCa1 independent of the oil viscosity independent of the oil lubricating effect TCb1 MSCb MCb n approx. 60 ms n+1 Mechanical challenge for OLTC manufacturers! Seite 16 von 39

(within specified range) MCa MSCa TCa1 independent of the oil viscosity independent of the oil

17 Table of contents Part 1: 1. Introduction: working principle of an OLTC 2. Differences between OILTAP and VACUTAP OLTCs 3. The insulating oil as a key design parameter for OLTCs 4. Future development: Common Oil compartment? 5. Summary Seite 17 von 39

18 Two examples: electric arc in oil an in vacuum I=0,6 A (capacitive current at pre-selector) I= 2600 A Reference: Siemens AG Seite 18 von 39

19 OILTAP : Tungsten-Copper arcing contacs VACUTAP : Vacuum Interrupters two typical diverter switch contact systems Seite 19 von 39

20 OILTAP M-type after operations, installed in a network transformer VACUTAP VM-type after operations, installed in an electric arc furnace transformer Seite 20 von 39

21 VACUTAP: conservative switching behavior relating to the insulating oil HVDC-applications Key success factors for all applications electric arc furnace operation sealed power transformers alternative liquids operation at explosion prone sites Seite 21 von 39

22 Table of contents Part 1: 1. Introduction: working principle of an OLTC 2. Differences between OILTAP and VACUTAP OLTCs 3. The insulating oil as a key design parameter for OLTCs 4. Future development: Common Oil compartment? 5. Summary Seite 22 von 39

23 Key Design Parameter Transformer Tap Selector Tap Changer arc-breaking in oil Diverter Switch vacuum switching type Electrical Insulation Cooling Arc-breaking capability Viscosity Lubrication Material Compatibility : very important : important The tap-changer requires additional capabilities of the liquid The tap-changer is the decisive component for the applicability of alternative insulating liquids Seite 23 von 39

24 Table of contents Part 1: 1. Introduction: working principle of an OLTC 2. Differences between OILTAP and VACUTAP OLTCs 3. The insulating oil as a key design parameter for OLTCs 4. Future development: Common Oil compartment? 5. Summary Seite 24 von 39

25 VACUTAP technology enables possibility for common oil compartment I No oil dissociation by electric arcs I Less gassing I due to special dimensioning of the transition resistors I no influence on transformer DGA measured I First 40MVA pilot applications are already online 40 MVA power transformer with common oil compartment source: Newsletter In-sight, 01/2014, 40 MVA hermetically sealed transformer with common oil compartment source: Stirl, Harthun, Frotscher: Offshore-Einsatz - Eine Herausforderung für den Transformator, Stuttgarter Hochspannungs-Symposium 2012 Seite 25 von 39

26 Table of contents Part 1: 1. Introduction: working principle of an OLTC 2. Differences between OILTAP and VACUTAP OLTCs 3. The insulating oil as a key design parameter for OLTCs 4. Future development: Common Oil compartment? 5. Summary Seite 26 von 39

27 Summary Part 1 1. Fluctuating mechanical parameters of the insulation oil are a challenge for each OLTC manufacturer. 2. In general, the OLTC requires additional capabilities of the insulation liquid. 3. VACUTAP OLTCs are treating the oil more conservative than OILTAP OLTCs due to the missing electric arc in the insulation oil. 4. Prospect: VACUTAP will enable common oil compartments. Seite 27 von 39

28 OIL ANALYSIS IN OLTC Table of contents Part 2: 1. Chemical reactions of the oil 2. Analyses 3. Integrated Systems 4. Advantages 5. Summary Seite 28 von 39

29 SCHEMATIC DIAGRAM OF THE SYSTEM - TRANSFORMER WITH ON-LOAD TAP-CHANGER VAC barrier board R transformer tank selector tank Seite 29 von 39

30 REACTIONS IN THE OIL OLTC BASED ON CONTACT WITH AIR AND HUMIDITY Influence Reaction Air/Oxygen (O 2 ) Water/Oxygen (H 2 O)/(O 2 ) Water (H 2 O) C C C OH C C C C C C O-O. C C C CHO O C C C COOH C C C COO-H + Mineral oil Effects Highly reactive peroxide radicals Alcohols, aldehydes, ketones and organic acids Separated organic acids Commencement of oil aging Oil degradation products (Sludge) Corrosion Analysis Interfacial tension Neutralization number/acid number Seite 30 von 39

31 REACTIONS IN THE OIL ON-LOAD TAP-CHANGER BASED ON ENERGY Influence Energy (thermal or electrical) Reaction Mineral oil C C C C C. H 2, CH 4, C 2 H 2, C 2 H 4, CO Effects Highly reactive carbon radicals Dissolved gases Analysis Commencement of oil aging Dissolved gases due to breakup of oil structures Thermal energy DGA analysis Electrical energy DGA analysis of gas sample: H 2 C 2 H 2 CH 4 C 2 H 6 C 2 H 4 CO H 2 C 2 H 2 CH 4 C 2 H 6 C 2 H 4 CO Seite 31 von 39

32 OVERVIEW OF ANALYSIS SCOPE ON-LOAD TAP-CHANGER OIL DGA (dissolved gases in the oil) Colour number Interfacial tension Moisture content Disruptive voltage Solids Neutralization number/ acid number Impurities Seite 32 von 39

33 INTEGRATED MONITORING SYSTEM WITH COMPETENT PARTNERS LABORATORY ANALYTICS I Disruptive voltage I Interfacial tension I Acid number I ONLINE ANALYTICS I I I DGA (2-5 gases) Humidity Temperature with simple and robust systems TECHNICAL EXPERTISE I Transformer I On-load tap-changer I Chemistry I Physics I Data evaluation INTEGRATED MONITORING SYSTEM TECHNICAL EXPERTISE ONLINE LABORA- TORY I I Bringing together laboratory and online data with technical expertise results in increased operating reliability and plannable maintenance in the short-term Together with further qualification of the employees, cost reductions and longer operating times can be expected in the medium term I In the longer term, the establishment of a large database of normal and faulty operating conditions leads to an extended knowledge base, improved analysis methods, better interpretation models and improved standards. Seite 33 von 39

34 ADVANTAGES AT A GLANCE High Influence Operating reliability Plannable maintenance Cost reduction Optimization of operating time Buildup of knowledge Buildup of qualifications Low Short-term Medium-term Long-term Operating time Seite 34 von 39

35 OIL ANALYSIS IN OLTC Summary Part 2 I Oil analysis helps to gain knowledge about the OLTC I A clever combination of laboratory and online analysis and expertise can help optimizing operation I Growing knowledge about the OLTC leads to continuous improvement Seite 35 von 39

36 CASE STUDY VACUTAP VR in a Power Transformer I Sudden increase of acetylene and hydrogen content monitored with an online DGA system in the selector compartment I Inspection of was done I Result: A nut had come loose and fallen off the terminal for the tap lead. Seite 36 von 39

37 CASE STUDY: DGA DATA Seite 37 von 39

38 CASE STUDY: PICTURES Seite 38 von 39

39 Seite 39 von 39

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