Sammendrag
The technology and the operational patterns of HVDC links are changing, and
therefore, the type test requirements for mass-impregnated non-draining HVDC
cables are currently being reconsidered. A CIGRÉ working group is preparing a
revised type test recommendation. Measurements and numerical modelling (without
any connection to the CIGRÉ effort) of the of internal pressure, temperature and
electric eld distributions in mass-impregnated non-draining cables subjected to
different environmental and loading conditions have recently been carried out. With
basis in this work, it is discussed and assessed how well the loading cycle and
polarity reversal test duties applied in the existing type test reect the stresses such
cables may experience in service. In particular, the potential risk associated with
formation of shrinkage cavities after load reduction is considered. Most of the
provisions in the existing type test are found to be appropriate and reasonable, but a
few possible improvements are proposed. Including a preconditioning procedure
prior to the load cycling duties could make the type test more realistic as it would
also include the contributions to the internal pressure from slow deformations of the
lead and polyethylene sheaths. Moreover, introducing load cycling duties with
currents beyond the rated load current and with shorter loading times (e.g., 0.5, 1 or
2 h) and at an intermediate ambient temperature (e.g., 20–30 °C) as a part of the
dielectric tests could qualify a mass-impregnated non-draining cable for temporary
overloading.
therefore, the type test requirements for mass-impregnated non-draining HVDC
cables are currently being reconsidered. A CIGRÉ working group is preparing a
revised type test recommendation. Measurements and numerical modelling (without
any connection to the CIGRÉ effort) of the of internal pressure, temperature and
electric eld distributions in mass-impregnated non-draining cables subjected to
different environmental and loading conditions have recently been carried out. With
basis in this work, it is discussed and assessed how well the loading cycle and
polarity reversal test duties applied in the existing type test reect the stresses such
cables may experience in service. In particular, the potential risk associated with
formation of shrinkage cavities after load reduction is considered. Most of the
provisions in the existing type test are found to be appropriate and reasonable, but a
few possible improvements are proposed. Including a preconditioning procedure
prior to the load cycling duties could make the type test more realistic as it would
also include the contributions to the internal pressure from slow deformations of the
lead and polyethylene sheaths. Moreover, introducing load cycling duties with
currents beyond the rated load current and with shorter loading times (e.g., 0.5, 1 or
2 h) and at an intermediate ambient temperature (e.g., 20–30 °C) as a part of the
dielectric tests could qualify a mass-impregnated non-draining cable for temporary
overloading.