Experiences With cable faults located at metallic screen connections

Overheating of metallic ground screen connections at accessories of single core cables are the root cause of severe insulation failures in the distribution network. The overheating is due to a high transition resistance of the connections combined with high induced currents in the ground screens during operation. For copper screened cables equipped with a metallic laminate, overheating causing failures are also observed randomly along the cables often at locations close to cable straps or cleats. Currently there are no international standards with complete tests to determine the ampacity of ground screen connections for different cable system designs making future installations more reliable. Furthermore, product information from the suppliers indicates that basis for design and test criteria is not uniform, and tests are not performed concerning relevant operation and fault scenarios. A research project is launched in Norway, to test different ground screen connections and then to provide guidelines to ensure proper future installations. A new CIRED working group is proposed to provide recommendations for complete tests of ground screen connections lacking in current international standards and brochures.publishedVersio

Condition Assessment of Wind Farm Medium Voltage Cable Joints

Rapid aging and failure in wind-farm collector systems has become an issue for grid owners. PD measurements of the cable systems can give good diagnostics, detect aging and pinpoint faults. Different PD measuring techniques are used today and the results will vary with applied voltage and frequency. This master thesis deals with preparation, electrothermal aging and characterization of XLPE cable joints. Dissection of the test objects was performed after aging and characterization. For characterization a variable frequency PD measurement setup has been built. The setup is defined by being able to detect PD with high accuracy in test objects at ± 17 kVpeak using Omicron MPD600 measuring equipment at variable frequencies between 10 mHz and 100 Hz. A PD-free low-pass RLC filter had to be used in the setup to reduce noise from the high-voltage source. The most important findings are that PD measurement results will vary significantly with regards to measuring technique. Aging may not be detected when measuring with too low frequency or voltage

Condition Assessment of Wind Farm Medium Voltage Cable Joints

Rapid aging and failure in wind-farm collector systems has become an issue for grid owners. PD measurements of the cable systems can give good diagnostics, detect aging and pinpoint faults. Different PD measuring techniques are used today and the results will vary with applied voltage and frequency. This master thesis deals with preparation, electrothermal aging and characterization of XLPE cable joints. Dissection of the test objects was performed after aging and characterization. For characterization a variable frequency PD measurement setup has been built. The setup is defined by being able to detect PD with high accuracy in test objects at ± 17 kVpeak using Omicron MPD600 measuring equipment at variable frequencies between 10 mHz and 100 Hz. A PD-free low-pass RLC filter had to be used in the setup to reduce noise from the high-voltage source. The most important findings are that PD measurement results will vary significantly with regards to measuring technique. Aging may not be detected when measuring with too low frequency or voltage

Standardization and contingency storage for submarine cable systems

publishedVersio

Standardization and contingency storage for submarine cable systems

publishedVersio

Experiences With cable faults located at metallic screen connections

Overheating of metallic ground screen connections at accessories of single core cables are the root cause of severe insulation failures in the distribution network. The overheating is due to a high transition resistance of the connections combined with high induced currents in the ground screens during operation. For copper screened cables equipped with a metallic laminate, overheating causing failures are also observed randomly along the cables often at locations close to cable straps or cleats. Currently there are no international standards with complete tests to determine the ampacity of ground screen connections for different cable system designs making future installations more reliable. Furthermore, product information from the suppliers indicates that basis for design and test criteria is not uniform, and tests are not performed concerning relevant operation and fault scenarios. A research project is launched in Norway, to test different ground screen connections and then to provide guidelines to ensure proper future installations. A new CIRED working group is proposed to provide recommendations for complete tests of ground screen connections lacking in current international standards and brochures