HIGH-VOLTAGE CABLE TESTING: TYPE TEST EXPERIENCES AND NEW INSIGHTS INTO PRE-QUALIFICATION Edwin Pultrum, Wouter Sloot, Joaquin Fernandez, René Smeets Presenter: René Smeets PhD, FIEEE Innovation manager KEMA Laboratories of DNV GL 1 SAFER, SMARTER, GREENER
Underground cable test requirements Extruded cables 150 kv: - type test, sample test, routine tests - IEC 60840 To cover design, production of cable and accessories Extruded cable > 150 kv: - additional prequalification (PQ) tests defined - IEC 62067 (2011) To cover long term reliability of cable systems 2
Classification of (cable) tests Development tests: Tests made during the development of the cable system. Prequalification test: Test made before supplying a type of cable system, in order to demonstrate satisfactory long term performance of the complete cable system. Type tests: Tests made before supply of a type of cable system, in order to demonstrate satisfactory performance characteristics of an application. Routine tests: Tests made by the manufacturer on each manufactured component (length of cable or accessory) to check that the component meets the specified requirements. Sample tests: Tests made by the manufacturer on samples of complete cable or components taken from a complete cable or accessory, at a specified frequency, so as to verify that the finished product meets the specified requirements. Tests after installation: Tests made to demonstrate the integrity of the cable system as installed. 3
Prequalification tests Long term AC voltage test with heating cycles: - 1.7 U0 applied during one year - test-loop is subjected to 180 heating cycles - heating up to the maximum operating conductor temperature - each heating cycle minimum 24 h, 8 h heating; 16 h cooling - includes at least one of each type of accessory (joint, termination) - needs to be installed in different laying conditions (earth, duct, tunnel,..) - lightning impulse test on one or more samples applied after the one year period 4
Prequalification test layout 5
KEMA Laboratories, Arnhem, Netherlands High-Power Laboratory 6 High-Voltage Laboratory
Thermal control Conductor temperature cannot be measured in the cable loop under voltage A dummy loop at ground potential, heated by the same current is used as reference It is essential that dummy and energized loop are located in the same thermal environment and close to each other energized loop 7 dummy loop
Heating cycles and recommendations 180 cycles of each 24 h during one year leaves room for interpretation KEMA Labs recommendations: - Heating cycle should not exceed 24 h - In case accessory components are designed for lower current (eg. GIS connectors), the heating duration may be extended, not the cooling (16 h) - Each quarter (3 month period) should contain 45 heating cycles - Remaining time voltage only Interruptions of PQ test cannot be avoided Handling of interruptions is not defined KEMA Labs recommendations: - Interruption of heating acceptable if the 2 h stable platform can be reached - no voltage interruption during heating - no voltage interruption during cooling when conductor differs > 15 K from soil Conductor Sheet Ambient - 8
Laying conditions Test shall be independent of location Conductor shall reach maximum operating temperature Guidance is needed on what laying condition should be taken as a reference, eg stipulating an acceptable temp difference between conductor and sheath Combination in one test only when thermal environment do not differ too much (eg not combine in ground with exposed to the sun ) Dummy (reference) must be close to the hot spot to ensure the same thermal environment 9
Type test failure rate 21 years of type testing and accessories (1993 2013) 740 components tested (extruded cables and accessories): - IEC 60502: 6 30 kv MV - IEC 62840: 30 150 kv HV - IEC 62027: 150 500 kv HV 6 categories: - MV cable, around 20 tests per year - MV termination: indoor and outdoor - MV joint - HV cable - HV termination: outdoor and GIS termination - HV joint: straight through and cross-bonding 10
Type test failure rate cables and accessories 6 30 kv 740 samples tested 30 500 kv 25% of HV cable type tests do not result in certification; 10% in MV 50% of MV termination type tests do not result in certification; 25% in HV 40% of MV joint type tests do not result in certification; 30% in HV 11
Type test failure rate cables and accessories MV cables and accessories HV cables and accessories MV: accessories (40-60%) increases over time; cables constant at 10-15% HV: cable (20 25%) and accessories (15 20%) remains constant over time 12 31 October 2016
Conclusions Pre Qualification Test: Recommendation for IEC 62067: - avoid large different thermal environments - one location for conductor temperature measurement - 24 hour heating cycles - equally divide 180 cycles over the quarters - guidance how to treat interruptions Type Tests results: - MV joint/terminations have high test (> 40%, upto 85%) failure rate - HV cable/joints have failure rate > 25% Not a clear indication of a changing trend over 25 years, except MV accessories, clearly increasing (40% in 1993 to 60% in 2013) 13
Thank you for your kind attention! www.dnvgl.com rene.smeets@dnvgl.com SAFER, SMARTER, GREENER 14