EPR-insulated Cables Research Articles

Investigation of 22 kV silane cure TR-EPR cable

EPR-insulated cables for distribution power network are not commonly used in Australia. This is due to the higher DDF of common EPR cables when compared with XLPE that contributes to the power loss and economics in transmitting electricity. This led to the development of EPR called TR-EPR with significantly lower DDF and uses silane curing process to address concerns about cost-effectiveness. The thermal behavior of low DDF silane cure TR-EPR is investigated for 30 months of exposure to the maximum operating temperature of material. The physical changes in the samples throughout the long-term aging are examined to create an opportunity to model the expected life cycle of TR-EPR cable under thermal stress. The cross-linking characteristics of TR-EPR cable are also examined by ambient curing that simulates the storage condition for unused cable and by cable heating process that simulates the condition when the cable is energized. The results are tabulated for a better understanding of the time for the material to cross-link at various conditions. The improved partial discharge values after cross-linking are also presented.

Test procedures and lifetime data analysis for electro-thermal endurance characterisation of EPR-insulated cables

The endurance of EPR-insulated cables is investigated by means of laboratory tests on cable models aged by thermal and electrical stresses, single or combined. The electrical, thermal and multi-stress life lines obtained by tests carried out according to a factorial procedure are reported. A significant contribution to plot the life lines is provided by the combined analysis method, which allows the electro-thermal life surface to be drawn. Indices for electrical, thermal and combined-stress endurance characterisation can thereby be supplied. The test results give high values of electrical, thermal and multi-stress endurance coefficients for the tested cables. This confirms the good electrical and thermal behaviour of EPR-insulated cables. Finally, a comparison of the results with a life model, able to provide life estimations, is made, obtaining good data fitting.

An insight into thermal life testing and characterization of EPR-insulated cables

Conventional and analytical procedures for thermal endurance characterization of insulating materials, described in IEC Standards, are applied to EPR-insulated cable models. Close results are obtained by the two procedures, provided that the diagnostic properties, the end points and the test temperatures are carefully chosen. Moreover, the thermal endurance indices do not vary using either the Arrhenius model, assumed by IEC 216, or the Eyring model. However, modifications of the life models are required in order to take into account the compensation effect, which has been observed for the diagnostic properties and the end points considered for thermal endurance characterization. The comparison of the values of the thermal endurance indices obtained for EPR-insulated cable models with those derived in the past for XLPE cable models shows that the tested EPR has slightly better thermal endurance characteristics.

Accelerated cable life testing of EPR-insulated medium voltage distribution cables

This paper presents results aimed at developing a reliable accelerated aging tank test for EPR-insulated cables. Aging was performed at 2 to 4 times rated voltage on load cycling to temperatures of 45/spl deg/C, 60/spl deg/C, 75/spl deg/C, and 90/spl deg/C at the conductor with water in the conductor strands and outside the cable. Results show that cable failure is more rapid at the highest electrical stress and lowest conductor load cycle temperature. Cables aged at higher temperatures and various levels of electrical stress rarely failed and retained in excess of 40% of their original breakdown strength after 1500+ days of aging. Aging performed at 90/spl deg/C load cycle temperature and 4 times rated voltage with air on the outside and water at the conductor of the cable showed more rapid loss of life than with water outside. Results indicate the optimum aging conditions for EPR-insulated cables in the accelerated cable life test (ACLT) differ significantly from those previously observed for XLPE-insulated cables, and that the appropriate test methodology for EPR-insulated cables requires additional study.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evaluation of ethylene-propylene rubber as electrical insulating material for a superconducting cable

Mechanical and electrical properties of ethylene propylene rubber (EPR) pieces were studied in comparison with polyethylene (PE) in the cryogenic temperature region to examine the possibility of its use as solid electrical insulating material in superconducting cables. The mechanical properties of EPR are preferable to those of PE mainly because of its low shrinkage. The electric strength and dielectric loss tangent of EPR are comparable with those of PE at liquid helium temperature. Based on the encouraging results, an extruded EPR-insulated cable was fabricated and its 15-m length was cooled down to liquid helium temperature successfully. Partial discharge experiments at that temperature showed good electrical characteristics. This is a breakthrough in terms of the electrical insulation design of cryogenic cables. >

Electrical Breakdown of Epr-Insulated Cables at DC and Impules Voltages

The electric strengths of three EPR-compounds are investigated using dc, impulse and impulse with dc bias voltages. To see whether dc and impulse strengths are affected by vulcanization residues, breakdown tests are carried out at different times after vulcanization. Different levels of dc perstress cause a considerable influence on the impulse breakdown strength, whereas the duration of dc prestress seems to be without effect. The applied mode of test procedure affects the breakdown results considerably: the breakdown strength measured in a step test procedure is lower than that obtained by the application of a single impulse with high amplitude. This behavior is valid for both polarities of dc prestress. Finally, the effect of repeated impulse discharges on the long-term performance of dc stressed cables is studied. The coherence between cable length, transient voltages, and cable failures is investigated and discussed.

Recent Developments in EPR-Insulated High-Voltage Cables

The main properties of ethylene propylene rubber (EPR) compounds for the insulation of high-voltage power cables are summarized in comparison with those of other solid dielectrics; the discharge resistance of EPR is emphasized. Construction and installation data, as well as electrical acceptance and qualification test results for four EPR-insulated cables rated from 20 to 60 kV are given; attention is drawn to the installation of a 45-kV cable, 800 meters long, directly buried in the ground, in service in an industrial plant since January 1965.