1. JWG A2/B4-28 HVDC Converter Transformers Progress Report Convener: Milan Saravolac IEC SYMPOSIUM DELHI, January 2009

2. JWG A2/B4-28 Progress Report, January 2009 Contents  Meetings  JWG Members – current status  JWG Report Summary

3. JWG A2/B4-28 Progress Report, January 2009 Meetings  Paris, 30 th August 2004, Inaugural  Arnhem (KEMA), 27 th January 2005  Bangalore, 21 st September 2005 (SC B4 Colloquium)  Rapperswil (Weidmann), 27 th January 2006  Paris, 28 th August 2006  Sao Paulo, 15 th & 16 th February 2007  Osaka, 29 th & 30 th October 2007  Ludvika, 11 th and 12 th March 2008  Nuremberg, 10 th and 11 th June 2008  Paris, 25 th August 2008  Delhi, 27 th January 2009

4. JWG A2/B4-28 Progress Report, January 2009 JWG Members – January 2009

5. JWG A2/B4-28 Progress Report, January 2009  Reliability Questionnaire – Update for 2005 & 2006 JWG Progress Summary 2005 – 2006 vs 2003-2004 The total failure rate decreasing…

6. JWG A2/B4-28 Progress Report, January 2009  Reliability Questionnaire – Update for 2005 & 2006 JWG Progress Summary 2001 – 2006 Decrease in actual failures and increase in prevented failures

7. JWG A2/B4-28 Progress Report, January 2009 JWG Progress Summary

8. JWG A2/B4-28 Progress Report, January 2009  Design Review Guide HVDC Converter Transformers The new guide is based on and derived from the existing document, “Guidelines for Conducting Design Reviews for Transformers 100 MVA and 123 kV and above” created by the CIGRE WG 12.22 and published in 2002 as CIGRE Brochure No. 204 Progress Summary

9. JWG A2/B4-28 Progress Report, January 2009  POLARITY REVERSAL TEST The dielectric stress depends on the polarization time and oil resistivity. Oil conductivity of the new oil and the aged oil differs considerably. Conductivity of oil impregnated high density pressboard remains almost Transient dielectric field simulations were performed with different values of oil conductivity in order to relate stress profiles during service with design values and stresses experienced during tests. JWG Progress Summary

10. JWG A2/B4-28 Progress Report, January 2009 EFFECT OF POLARIZATION DURATION AND DIFFERENT OILS JWG Progress Summary

11. JWG A2/B4-28 Progress Report, January 2009  Five different combinations of test voltage and time duration were simulated  PR test with 20% higher than test level Upr = 1.5((N-0.5)Udm +0.35Uvm)) and 45 min longer duration (90-120-90 min) was most suitable. JWG Progress Summary

12. JWG A2/B4-28 Progress Report, January 2009  Effect of Oil Conductivity –Oil conductivity is not measured on a regular basis –There is no consistent test method for measuring –The test method measures conductivity at dielectric stress below 0.5 kV/mm –In PR test oil can be subjected to 5-10 kV/mm –In service oil is different form the one used in testing –No information about real effectiveness of the PR test. JWG Progress Summary

13. JWG A2/B4-28 Progress Report, January 2009  Tutorial –The Tutorial on Reliability of HVDC Converter Transformers is complete as well and was initially presented at the CIGRE Brazil event (Workspot) in Belem in April 2008. The intention is to present this tutorial during the next A2 Colloquium in South Africa in August 2009 –Tutorial for B4 shall be scheduled JWG Progress Summary.

14. JWG A2/B4-28 Progress Report, January 2009 Action Plan  By the 2009 B4 Symposium, to issue the Design Review Guide.  By Aug 2009 to issue a Final Report.

15. JWG A2/B4-28 HVDC Converter Transformers Thank you for your attention