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Medium Voltage Cable Testing Technologies Presented by: Craig Goodwin Most Commonly Used Cable Testing Methods Energization Sources: • DC and DC Leakage Methods (Insulation Resistance) • Damped AC (20-300 Hz) • AC – Power Frequency • AC – Low Frequency (VLF – 0.1 Hz) Most Commonly Used MV Cable Testing Methods Cable Diagnostic Technique: • • • • • • • Withstand Tan Delta / Dissipation Factor Partial Discharge (Online and Offline) TDR (Time Domain Reflectometry) Thermal Imaging Others Combination of the Above - Smart Online versus Offline • Online testing is generally easier to carry out, and is so called “nondestructive” its effectiveness is also limited.. • Offline testing, while requiring more preparation and setup, provides more insight into the cables true condition. IEEE MV Cable Field Testing Chart IEEE 400 (OmniBus) - 2012 Guide for Field Testing & Evaluation of the Insulation of Shielded Power Cable Systems Rated 5kV and above IEEE 400.1 IEEE 400.2 – 2013 IEEE 400.3 Field Testing of Laminated Cables Rated 5kV and above using DC. Field Testing of Shielded Power Cables using Very Low Frequency VLF PD Testing of Shielded Power Cables in the Field Environment Note 1 – there is no IEEE 60Hz field withstand testing standard for MV Cables Note 2 – there is no IEEE DC field testing standard for any extruded cables. The Demise of the DC Hipot for Testing MV Cables • Potential Negative Impact on the Service Reliability of Extruded Cables • Ineffectiveness to Detect Serious Defects in Cable Insulation Ref: IEEE400-2012 Concentric Neutral Design Vs. Tape Shielded Cable Design Can Impact the Effectiveness and Usability of Certain Diagnostic Techniques That are Rich in Frequencies. Which Energization Source and Diagnostic Method/s to use and when………. Applicability Of Testing Methods IEEE 400 has an Informative Table in the Appendix on the Applicability of Various Testing Methods. Comments • Some Methods Were Not Analyzed Due to Lack of Information / Data. • Some Methods were shown to be useful and some were Not. • Table Does Not Address Tape Shielded Cables and Mainly Focuses on Utility Style CN Type. Test and Diagnostic Selection Matrix: Expanded from IEEE 400 - 2012 Method New Extruded Acceptance Shield Type Old Extruded Maintenance CN Old Hybrid Combo Mixed Unjacket Accessories ed (Splice & Term) CN Mixed Tape CN DC Withstand Testing X X X X X X Limited VLF AC Withstand Test Tan Delta / Dissipation Factor Test Partial Discharge Test – Offline Limited Limited Partial Discharge Test – Online Tape PILC Laminat ed Mixed Limited Limite Limited Limited Limited d Smart VLF W/S Test - combination with TD Smart VLF W/S Test - combination with PD TDR (Time Domain Reflectometry) Limited Useful Useful Not Useful Limited Limited Limited Limited Useful Useful Limited Useful Conclusions • Testing Organizations Need to Be Aware of the Changes in Standards and Guides • A Need to Inform and Educate Customers / End Users • Careful Consideration When DC is Requested • Choice of Test Method Often Determined By Age and Type of Cable and the Intended Defect Diagnosis • Often, a Testing Strategy Involving a Combination of Tests is Most Appropriate.
