Fluid characteristics impact performance capabilities in transformer application

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Morgan Davidson
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1 Fluid characteristics impact performance capabilities in transformer application Mineral Oil Natural Ester Synthetic Ester Silicone Oil Base Fluid Petroleum Oil Vegetable Oil Hydrocarbons Polydimethylsiloxanes Diagnostic Capability Yes Yes Yes Less Fire point 160 C 360 C 310 C 340 C Biodegradability Low Readily Readily No Oxidation Biobased No Yes No No Cellulose-based materials aging Compatibility / Miscibility Non-free breathing Very good Good Very good Good Free breathing Good Not applicable Very good Good Average Excellent Good Average Yes Yes Yes No

2 BDV results Tests results shows BDV equal or higher than Mineral Oil for all tested gaps and electrode shapes, including slightly inhomogeneous fields Permittivity is not the same Permittivity of NE is 35% higher, changing the electrical field distribution. This increases safety margin, since it shifts the voltage drop to solid insulation, reducing stress in the fluid. 2

3 Permittivity affects field distribution Calculation with MO Calculation with NE 3 Uniform in the center Higher concentration in the corners

4 Resultant BDV of NE and MO were equivalent in all cases. Superior to design curve. 4

Long gap tests confirming equivalent BDV 2000 LI 1.2µs x 50µs negative polarity AC 60 Hz (kv) 2000 600 500 400 300 200 100 NE Fluid Withstand (1%) Min.

5 Long gap tests confirming equivalent BDV 2000 LI 1.2µs x 50µs negative polarity AC 60 Hz (kv) NE Fluid Withstand (1%) Min. Oil Withstand (1%) NE Fluid Breakdown (avg) 60 Min. Oil Breakdown (avg) Fluid Gap (mm) SI 250µs x 2500µs - positive polarity Negative Lightning Impulse (kv) Fluid Gap (mm) NE Fluid Withstand (1%) Min. Oil Withstand (1%) NE Fluid Breakdown (avg) Min. Oil Breakdown (avg) Stress between Tap Changer contacts Positive Switching Impulse (kv) NE Fluid Withstand (1%) Min. Oil Withstand (1%) NE Fluid Breakdown (avg) Min. Oil Breakdown (avg) Fluid Gap (mm) 5

6 How much MO is acceptable? If MO content is above 7%, the classification of K class fluid, allowing the benefits for the installation. Fluid properties must be comparative 100% miscible 6 CONFIDENTIAL. This document contains trade secret information. Disclosure, use or reproduction outside Cargill or inside Cargill, to or by those employees who do not have a need to know is prohibited except as authorized by Cargill in writing.

7 CONFIDENTIAL. This document contains trade secret information. Disclosure, use or reproduction outside Cargill or inside Cargill, to or by those employees who do not have a need to know is prohibited except as authorized by Cargill in writing. Moisture Saturation

8 Viscosity 8 CONFIDENTIAL. This document contains trade secret information. Disclosure, use or reproduction outside Cargill or inside Cargill, to or by those employees who do not have a need to know is prohibited except as authorized by Cargill in writing.

9 Pour Point 9 CONFIDENTIAL. This document contains trade secret information. Disclosure, use or reproduction outside Cargill or inside Cargill, to or by those employees who do not have a need to know is prohibited except as authorized by Cargill in writing.

10 Testing / Site filling 10 It can be shown by calculation the design safety margins are sufficient for testing with MO and site filling with NE. The difference increases with the voltage class. Typically, up to 230kV it is not critical. Despite of some OEM s having a significant history of no issues, it is recommended to test and site fill with the same insulating liquid.

11 Annex 11 Presentation Title-Date

Dielectric Design: Partial Discharge Inception Voltage Even at higher moisture contents, NE PD inception voltage is quite superior to MO and SE.

12 Dielectric Design: Partial Discharge Inception Voltage Even at higher moisture contents, NE PD inception voltage is quite superior to MO and SE. NE and SE test with same ppm of water meaning lower % of saturation for SE Limit of Voltage for starting having PD at different temps and water contents (needle disc) for Ester Natural, Synthetic and Mineral Oil. Best results for NE. 12

13 Highly divergent fields study VARIATION OF ELECTRODES AND GAP DISTANCES Polished sphere Ø 13 mm Polished blunt point Ø 3 mm Polished blunt point Ø 0.8 mm Polished blunt point Ø 0.6 mm Gramophone needle Ø 0.12 mm Liquids under test Natural ester: Envirotemp TM FR3 fluid Mineral oil: Nynas Nytro Lyra X Relative moisture rh: Rel. Humidity < 12 % 13

14 Test Results LI Negative Polarity Needle - sphere Blunt point 3 mm - sphere Sphere - sphere Blunt point 0.8 mm - sphere Blunt point 0.6 mm - sphere 14

15 Thermal Conductivity It is a key parameter for defining the heat convection coefficient, especially for nonturbulent flow conditions. The copper to oil gradient benefits the convection inside the winding oil ducts Viscosity Pressure drop along winding must balance the generated pressure due to density difference, the thermosiphonic factor. Higher pressure drop requires larger density gradient, which means slightly increasing the top oil temperature. 15

16 Natural Ester Typical results when Mineral Oil transformers are filled with NE The balance between the cooling improving due to higher thermal conductivity and specific heat, versus the higher pressure drop due to higher viscosity 19 CONFIDENTIAL. This document contains trade secret information. Disclosure, use or reproduction outside Cargill or inside Cargill, to or by those employees who do not have a need to know is prohibited except as authorized by Cargill in writing.

Dr Joerg Friedel Product Application Specialist Shell Technology Centre Hamburg, Germany

Dr Joerg Friedel Product Application Specialist Shell Technology Centre Hamburg, Germany An inhibited transformer oil based on Shell gas-to-liquids (GTL) technology The evolution of hydrocarbon transformer