Experiences with cable faults located at metallic screen connections

Abstract

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.

Analysis of Cable Screen Currents for Diagnostics Purposes

“…Problems with cable screen connection exist due to a lack of standards, bad design, non-clear installation procedures, unskilled personnel, and a lack of information about the installation of power cables. The lack of information is a particularly big problem in the case of watertight cables, which consist of double screen layers, since different manufacturers have different recommendations regarding double screen earthing and taking into account second screen layer conductivity in cable specification [12]. The problematic state of cable screen connections is currently being analyzed by CIRED Working Group-Ground Screen Power Cable Connections-Test Recommendations for Ground Screen Power Cable Connections.…”