Periodic Reporting for period 2 - NEWGEN (New generation of HVDC insulation materials, cables and systems)
Reporting period: 2024-04-01 to 2025-09-30
The overall objective of NEWGEN is to develop and demonstrate new insulation materials, cable manufacturing solutions, online condition monitoring technologies, and comprehensive life and reliability modelling tools for next-generation of extruded high voltage direct current (HVDC) cables and cable systems, thereby fostering the reliability and resilience of the inter-connected European HVAC/-DC transmission grids. The project also supports the digitalization of the energy system by developing online monitoring and modelling tools for HVDC cable systems. Moreover, the project considers the sustainability and circular economy aspects of the new materials and technologies, as well as the social and economic impacts of the HVDC cable systems. The project's main objectives are to: (i) develop novel space charge mitigating additives and cable extrusion solutions for highly-reliable polymeric HVDC cables; (ii) develop and demonstrate a novel online global monitoring system for pre-fault detection and health status evaluation of HVDC cable systems; (iii) develop a comprehensive life and reliability model for HVDC cable systems under realistic operation conditions; and (iv) demonstrate the impact of more reliable HVDC cables on the firewall capability and overall reliability of inter-connected AC transmission systems.
By M36, several key technical and/or scientific achievements have been obtained in NEWGEN.
1. Optimized polypropylene (PP)- copolymer based thermoplastic base insulation blends with suitable dielectric and thermomechanical properties to be applied in HVDC cable insulation have been developed. Moreover, novel polymeric additives with grafted functional groups have been developed and tested as well-dispersing space charge mitigating additives in the PP insulation blends. The new PP insulation compounds with and without additives have been shown to exhibit improved dielectric and thermomechanical properties over state-of-the-art XLPE insulation, particularly at elevated temperatures where XLPE shows reduced performance. For instance, higher short-term breakdown strength and significantly reduced space charge accumulation in comparison to XLPE has been demonstrated with the best-performing PP insulation compounds.
2. New design for the insulation distributor and screw was developed for thermoplastic PP based compounds and used in conjunction with several different material compounds to produce prototype HVDC cables. Thermoplastics dedicated extrusion crosshead has been type-tested by producing HVDC cable prototypes. Three different insulation distributor designs have been tested and modelled. Simulations have been found to match color test results relatively well, which gives validity to simulation approach in further optimization of the flow distributors. In total four full-size HVDC cable prototypes (with different processing conditions and base insulation blends) and six reels of model “A” cable have been produced between M19-M36.
3. The measurement approach for Partial Discharges under DC voltage stresses has been consolidated in terms of measurement chain, acquisition configuration and long term monitoring, and the ability to measure PDs well below 100 pC threshold has been established. Artificial defects have been designed and manufactured to characterize the short term physical behaviour and the long term degradation rate of the materials in the presence of various typologies of defects (internal, surface and corona). A large number of PD acquisitions has been carried out, contributing to the creation of a database with more than 2000 acquisitions. Regarding the development of the leakage current sensor based on a magneto-optical method, a working prototype and its calibration procedures were developed. Performance tests were performed; 1 mA currents were measured in a controlled environment.
4. The development of the life model for HVDC cable systems is complete. The novel developed model is now capable to estimate the life and reliability of HVDC cables under the following working stresses: rated (design) electrical and thermal stresses, load cycles, voltage polarity reversals (VPRs), Voltage transients during disturbances and contingencies. Moreover, optimization of Bipolar Charge Transport model parameters at various temperatures and electric fields, and accelerated life tests on SoA DC-XLPE and the novel PP ternary blends with the life model fitting and statistical post processing have been performed.
1. Optimized polypropylene (PP)- copolymer based thermoplastic base insulation blends with suitable dielectric and thermomechanical properties to be applied in HVDC cable insulation have been developed. Moreover, novel polymeric additives with grafted functional groups have been developed and tested as well-dispersing space charge mitigating additives in the PP insulation blends. The new PP insulation compounds with and without additives have been shown to exhibit improved dielectric and thermomechanical properties over state-of-the-art XLPE insulation, particularly at elevated temperatures where XLPE shows reduced performance. For instance, higher short-term breakdown strength and significantly reduced space charge accumulation in comparison to XLPE has been demonstrated with the best-performing PP insulation compounds.
2. New design for the insulation distributor and screw was developed for thermoplastic PP based compounds and used in conjunction with several different material compounds to produce prototype HVDC cables. Thermoplastics dedicated extrusion crosshead has been type-tested by producing HVDC cable prototypes. Three different insulation distributor designs have been tested and modelled. Simulations have been found to match color test results relatively well, which gives validity to simulation approach in further optimization of the flow distributors. In total four full-size HVDC cable prototypes (with different processing conditions and base insulation blends) and six reels of model “A” cable have been produced between M19-M36.
3. The measurement approach for Partial Discharges under DC voltage stresses has been consolidated in terms of measurement chain, acquisition configuration and long term monitoring, and the ability to measure PDs well below 100 pC threshold has been established. Artificial defects have been designed and manufactured to characterize the short term physical behaviour and the long term degradation rate of the materials in the presence of various typologies of defects (internal, surface and corona). A large number of PD acquisitions has been carried out, contributing to the creation of a database with more than 2000 acquisitions. Regarding the development of the leakage current sensor based on a magneto-optical method, a working prototype and its calibration procedures were developed. Performance tests were performed; 1 mA currents were measured in a controlled environment.
4. The development of the life model for HVDC cable systems is complete. The novel developed model is now capable to estimate the life and reliability of HVDC cables under the following working stresses: rated (design) electrical and thermal stresses, load cycles, voltage polarity reversals (VPRs), Voltage transients during disturbances and contingencies. Moreover, optimization of Bipolar Charge Transport model parameters at various temperatures and electric fields, and accelerated life tests on SoA DC-XLPE and the novel PP ternary blends with the life model fitting and statistical post processing have been performed.
Novel grafted PP additives with polar functionalization have been developed for controlling the charge trapping and transport properties in HVDC cable insulation blends. Up-scaling and pilot-scale clean compounding of the novel PP insulation blends has been achieved at 3000+ kg scale in total, yielding optimized PP insulation blends for model “A” and full-size HVDC cable prototype production in NEWGEN. The short-term dielectric characterization results obtained in WP1 for the PP insulation blends show improved performance in comparison to the DC-XLPE.
Extrusion technologies for HVDC cables have advanced with the addition of a new triple crosshead which is type tested and released for sales. This can be commercially exploited during the next year (2026).
The validation of the measurement chain and configuration has allowed for the design of the first blocks for monitoring partial discharge phenomena. Since there are no commercially available devices for this purpose, this is considered to be innovative beyond the state of the art. The setup used for man-operated measurements, together with a proper control and elaboration software that is under development, could be commercially exploited. Another promising result is the development of a comprehensive life and reliability model for HVDC cables of different sizes, from cable models to full-size cable lengths, accounting for the enlargement of insulation volume. This model can be applied to cables working under different conditions, including constant electro-thermal stress, load cycles, and voltage transients.
The WP4 progress until now has contributed significantly to the impact outcome “Life and reliability model for HVDC cable systems”, since in fact a comprehensive life and reliability model for HVDC cable systems (including accessories, i.e. joints and terminations) has been developed, which is capable to account for electrical and thermal stresses applied to the cable insulation during tests and in service, namely cycles of load current, long temporary overvoltages and voltage polarity reversals. Moreover, an optimized life-based cable design procedure has been set up. The model parameters have been derived for the state-of-the-art DC-XLPE so far. They will be determined also for PP-based compounds with and without additives after the completion of the validation campaign of the model by means of Accelerated Life Tests (ALTs) on such selected PP-based compounds.
Extrusion technologies for HVDC cables have advanced with the addition of a new triple crosshead which is type tested and released for sales. This can be commercially exploited during the next year (2026).
The validation of the measurement chain and configuration has allowed for the design of the first blocks for monitoring partial discharge phenomena. Since there are no commercially available devices for this purpose, this is considered to be innovative beyond the state of the art. The setup used for man-operated measurements, together with a proper control and elaboration software that is under development, could be commercially exploited. Another promising result is the development of a comprehensive life and reliability model for HVDC cables of different sizes, from cable models to full-size cable lengths, accounting for the enlargement of insulation volume. This model can be applied to cables working under different conditions, including constant electro-thermal stress, load cycles, and voltage transients.
The WP4 progress until now has contributed significantly to the impact outcome “Life and reliability model for HVDC cable systems”, since in fact a comprehensive life and reliability model for HVDC cable systems (including accessories, i.e. joints and terminations) has been developed, which is capable to account for electrical and thermal stresses applied to the cable insulation during tests and in service, namely cycles of load current, long temporary overvoltages and voltage polarity reversals. Moreover, an optimized life-based cable design procedure has been set up. The model parameters have been derived for the state-of-the-art DC-XLPE so far. They will be determined also for PP-based compounds with and without additives after the completion of the validation campaign of the model by means of Accelerated Life Tests (ALTs) on such selected PP-based compounds.