Diagnostic Measurements on Power Transformers Problems Resulting from Deregulation •With deregulation of the energy markets, the life span of electrical assets becomes critical. o All assets including all transformers have to be in service as long as possible. transformers this can mean continuous operation over the life span of the asset at full load or even more since redundant transformer assets are not available. o For Introduction May 10 PAGE 2 Situation in Germany (and other countries) Situation Today •Many of the transformers in Germany have an age of 25-30 years 100 •A large percentage of transformers are in service for more than 25 years – with the health of the transformers not often known. •About 35% - 40 % of all transformer faults are caused by breakdowns in the aged insulation. No. of transformers 90 80 70 60 50 40 30 20 10 0 1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 Betriebsalter der Transformatoren in Jahren Age of transformers / years Problem: faults happen more often with increasing age May 10 PAGE 3 May 10 PAGE 4 Generator Transformer 27/400kV Causes of Ageing o HV Bushing Measuring Tap LV Bushing Dielectric causes Electromagnetic causes Thermal causes Chemical causes o o o Diverter Switch Tap Selector Tapped Winding High Voltage Winding Low Voltage Winding May 10 PAGE 5 May 10 PAGE 6 Core Michael Krüger e Marcelo Paulino - São Paulo maio/2010 1 Diagnostic Measurements on Power Transformers Dielectric Causes of Ageing • Electromagnetic Causes of Ageing •High currents (e.g. due to short circuits nearby the transformer) produce high mechanical forces o Deformation o Damage • Electrical stress particularly in areas with high electrical field strengths •Dielectric losses produce heat •Decomposition of solid and liquid insulation by partial discharges •Generation of gases •Generation of acids and sludge •Generation of X-wax of the winding of the paper insulation (cracks) , particularly on aged of partial discharges of partial break-downs parts o Initiation o Initiation May 10 PAGE 7 May 10 PAGE 8 Thermal Causes of Ageing • Hysteresis losses in the magnetic core • Shorted laminates • Ohmic losses in the windings • Dielectric losses in the insulation • Load changes will cause warming up and cooling down - negative influence on the lifetime of the insulation • The ageing of the insulation is accelerated by a factor 2, if the temperature is increased by 7°C (valid for normal operation temperatures) Chemical Causes of Ageing •Organic acids are produced as a result of ageing o In particular, they affect the paper insulation •-> accelerated ageing o Metals like Copper, Iron, Aluminium and Zinc are behaving like catalysts •-> accelerated ageing May 10 PAGE 9 May 10 PAGE 10 Ageing of the Cellulose by Acids Ageing in the Cellulose Ageing of Cellulose is caused by: • the influence of oxygen Oxidation • the influence of water Hydrolysis • the influence of heat Microstructure of paper with Neutralization Number [mg/kg] (from left to right) 0.05 0.1 0.2 0.3 Pyrolysis May 10 PAGE 11 May 10 PAGE 12 Michael Krüger e Marcelo Paulino - São Paulo maio/2010 2 Diagnostic Measurements on Power Transformers Ageing of Paper As the cellulose ages, the glucose ring chains break (depolymerisation). The following substances are produced: • Water • Gases (CO, CO2) • Aldehyde Groups (Alkaline) • Carboxyl Groups (organic acids) H 2COOH C CH H OH C H May 10 Water as Ageing Factor Water accelerates the ageing of the Cellulose: 1000 relative speed of depolymerisation Relative Depolymerisationsgeschwindigkeit 80 ° C 100 ° C 100 120 ° C H2 O OH H C CH 10 1 0 1 2 Wassergehalt in paper water contentim Papier 3 [%] 4 O CH O C H C OH H OH CH H2COOH C H O To extend the lifetime, the water has to be removed from the insulation! PAGE 13 May 10 PAGE 14 Insulation Oil Analysis Measurements Dielectric measurements Physical measurements • Chemical measurements Gas in oil-Analysis Furane analysis Conclusions Condition of the oil Electrical condition of the transformer Condition of the Cellulose Dielectric, Physical and Chemical Analysis Dielectric measurements Breakdown voltage Dielectric dissipation factor Physical properties Refraction number Density Kinematic viscosity Flash point Pour Point Interfacial tension Colour and Purity Chemical properties Water content in oil Neutralization number Saponification number Sulphur content Chloride content Inhibitor content (IR Meth.) Standard VDE 0370 T5 = IEC 60156 VDE 0380 T2 = IEC 60247 Standard DIN 51423 DIN 51757 DIN 51526-1 DIN EN 22719 DIN ISO 3016 ISO 6296 ISO 2049 / IEC 60296 Standard DIN IEC 814 = IEC 60814 DIN 51558 T2 IEC 60296 DIN 51559-2 DIN 51400-6 DIN 51577-3 IEC 666 May 10 PAGE 16 May 10 PAGE 15 Recommended Limits according to IEC 60422 Gas-in-Oil Analysis (DGA) Toepler pump for gas extraction Power & Instrument Transformers 170 kV – 420 kV Breakdown Voltage [kV] Dielectric Dissipation Factor @ 90° C Neutralization Number [mg KOH/g] Interfacial Tension [mN/m] Water Content [mg/kg] Power Transformers 72.5 kV – 170 kV Instrument Transformers < 170 kV Nitrogen N2 Oxygen O2 Water H2 Carbon monoxide CO Carbon dioxide CO2 Methane CH4 Ethane C2H6 Ethylene C2H4 Acetylene C2H2 Propane C3H8 Propene C3H6 May 10 PAGE 19 May 10 PAGE 18 Michael Krüger e Marcelo Paulino - São Paulo maio/2010 3 Diagnostic Measurements on Power Transformers Key Gases Interpretation of Gases and Gas Ratios May 10 PAGE 20 May 10 PAGE 23 DGA Diagnosis (Duval) Possible Faults May 10 PAGE 25 May 10 PAGE 26 Cellulose Possible Reasons Structure of Cellulose Decomposition products of Cellulose May 10 PAGE 27 May 10 PAGE 28 Michael Krüger e Marcelo Paulino - São Paulo maio/2010 4 Diagnostic Measurements on Power Transformers Furan Analysis Furan Analysis Cigré Proceedings WG D1.01.03 (formerly WG 15-01): •Furane derivates 5-hydroxylmethyl-2-furfural (5HMF) furfuryl alcohol (2FOL) 2-furfural (2FAL) 2-acetyl furan (2ACF) 5-methyl-2-furfural (5MEF) •Correlation to the Degree of PolymerizationWert o Averaged Polymerization (Length of the molecule chains of the Cellulose) o New paper: about 1000-1200 o Complete Degradation: