Published on January 9, 2008
Tan Delta / Dissipation Factor As An Effective Tool In Determining The Insulation Condition Of Power Cables Using The BAUR PHG VLF System. Craig Goodwin, HV Diagnostics Inc. GA, USAe-mail: [email protected]: Tan Delta / Dissipation Factor As An Effective Tool In Determining The Insulation Condition Of Power Cables Using The BAUR PHG VLF System. Craig Goodwin, HV Diagnostics Inc. GA, USA e-mail: [email protected] Summary of Presentation: Summary of Presentation Theory / Background Description of Diagnostic Method/s Field Examples Slide3: Benefits of Voltage Testing with VLF Sinusoidal Waveforms in the field. Low Power Requirement for on site testing. Compact portable design of test equipment. Easier diagnosis of water tree deteriorated insulation at low frequencies compared to higher frequencies such as 60Hz using TD. Easier to integrate Cable diagnostic interfaces such as TD and PD etc. Slide4: "WATER TREEING" in polymeric insulation (schematic layout) electrical field conditions for possible water development of disturbance field "water trees" time outer semiconducting layer insulation inner semiconducting layer conductor "bow-tie trees" "vented trees" Slide5: Vented- tree growing from the inner semicon layer of a 30 kV- PE- cable Slide6: Dielectric Failure of insulation originating from a water tree Slide7: What is Dissipation Factor ( tan d) ?? time/sec 0 10 voltage current = dissipation factor tan d = = Slide8: Simplified Dielectric Equivalent Circuit of a Water Tree >> Slide9: AC Pure Sinewave Output Voltage and Current. Slide10: Do I have a DF dependancy regarding the total length or the amount of joints in a cable? NO! Q & A Slide11: Voltage Dependence of 0,1 Hz Tan Delta on New and Service-aged XLPE-insulated Medium Voltage Cables. Slide12: Cables are still in good condition, if : tan d (2 Uo) < 1,2 ‰ and [tan d (2 Uo) - tan d (Uo)] < 0,6 ‰ Cables in bad condition (or to be replaced immediately ) if : tan d (2 Uo) ³ 2,2 ‰ or [tan d (2 Uo) - tan d (Uo)] ³ 1,0 ‰ EPR and TR - XLPE cables have higher absolute values of Tan Delta than the above XLPE values, however the change in Tan Delta is still the important criteria to take note of. Criteria For tan d – for PE or XLPE Slide13: Field Test Result for an 1974 XLPE Cable Good Result for an old Cable. Slide14: Field Test Result for an 1984 XLPE Cable Nominal Operating Voltage: Vo = 14kV PDIV: only at 19kV Note: TD values are poor even at Vo. Slide15: Comparison of Cable Diagnostic Systems Key: 0 OK + Pos. - Neg. Slide16: Other Applications and Techniques available using the Tan Delta measurement: Measurement of TD and Capacitance with respect to Frequency ( Dielectric Spectroscopy). Application of TD as a reference signature and method for determining moisture ingress for PILC cables. Slide17: Conclusions of Tan Delta Diagnostics A TD cable assessment system can clearly distinguish between new, medium and strongly aged extruded cable insulation. Water trees which are a major original source of insulation failures in aged extruded cables can be detected in a non-destructive manner. Excellent Field Results. To detect singular defects, a combined assessment system including the application of partial discharge measurement and location in addition to TD is necessary.