Periodic Reporting for period 1 - NEWGEN (New generation of HVDC insulation materials, cables and systems)
Periodo di rendicontazione: 2022-10-01 al 2024-03-31
The project's context is related to the European Green Deal and the decarbonization of the energy sector: NEWGEN contributes to the European Green Deal by enabling the long-distance transmission of electricity from renewable energy sources with minimal losses and increased reliability. The project also supports the digitalisation 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.
Project focus and main objectives. NEWGEN is a project that aims to develop and demonstrate new insulation materials, cable manufacturing solutions, online condition monitoring technologies, and life and reliability modelling tools for next-generation of extruded high voltage direct current (HVDC) cables and 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.
Project focus and main objectives. NEWGEN is a project that aims to develop and demonstrate new insulation materials, cable manufacturing solutions, online condition monitoring technologies, and life and reliability modelling tools for next-generation of extruded high voltage direct current (HVDC) cables and 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.
NEWGEN has developed new polypropylene (PP)-based thermoplastic base insulation blends with suitable dielectric and thermomechanical properties to be applied in HVDC cable insulation. 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 perfromance. 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. Cable Manufacturing Equipment Development:The development of the cable manufacturing equipment is progressing as planned. A new triple crosshead dedicated for thermoplastic PP-based (Polypropylene) materials has been developed, as well as several experimental insulation screw designs. Two sizes of cable with thermoplastic PP-based materials have been produced for the project: miniature power cables with 1.5 mm insulation and life-size HVDC (High Voltage Direct Current) cable prototypes. These cables will be used to characterize the material morphology and electrical performance, as well as the equipment and manufacturing process.
Detection of Partial Discharges: A literature study about the state of the art has been done related to the detection of partial discharges under DC conditions. Standard artificial defects have been defined (internal, surface, and corona), and the way to manufacture them with different materials (epoxy, XLPE (Cross-linked polyethylene) and PP) in order to have reproducible defects originating ‘controlled’ partial discharges. These defects have been stressed both under AC and DC conditions to characterize them electrically and understand the different physical conditions in order to be able, at a later point, to discriminate them. Moreover, the ageing and degrading effects of the defects have been studied through long-term tests. The more than 1500 tests performed in the period enabled to better understand the discharge process for different artificial defects, optimizing the measurement chain (from standard AC PD instruments) and the acquisition configuration that resulted in being different with respect to the standard AC conditions. Moreover, a database of known defects was started. In addition, trigger-based equipment was prototyped and validated in order to localize the source on a short cable through partial discharge signals.
Monitoring System Design: The listed activities allowed us to start the design of the architecture and the requirements for the monitoring system, which is currently under development.
Life and Reliability Model: A life and reliability model of HVDC cables has been developed for both constant electrothermal stress and periodic load cycles, as well as voltage transients like Voltage Polarity Reversals and Temporary Overvoltages. A procedure for life-based geometric design of HVDC cables has been set up for both constant and time-varying electrothermal stress. A Bipolar Charge Transport (BCT) model for charge carrier injection and transport in the insulation has been developed, and the algorithm for BCT model parameter optimization from space charge measurements done in WP1 has been set forth and applied to SoA (State of the Art) DC-XLPE under different values and polarities of the applied electric field. A deeper insight into macroscopic conductivity models has been gained by fitting 5 different literature models for conductivity from the literature to conductivity measurements vs. field and temperature. The effect of insulation volume enlargement from small specimens to large cables has been addressed using an ad hoc literature formula for HVDC cables working under different loads. Tools for the inter-connection pre-fault monitoring data vs. aging phenomena have also been set up.
Detection of Partial Discharges: A literature study about the state of the art has been done related to the detection of partial discharges under DC conditions. Standard artificial defects have been defined (internal, surface, and corona), and the way to manufacture them with different materials (epoxy, XLPE (Cross-linked polyethylene) and PP) in order to have reproducible defects originating ‘controlled’ partial discharges. These defects have been stressed both under AC and DC conditions to characterize them electrically and understand the different physical conditions in order to be able, at a later point, to discriminate them. Moreover, the ageing and degrading effects of the defects have been studied through long-term tests. The more than 1500 tests performed in the period enabled to better understand the discharge process for different artificial defects, optimizing the measurement chain (from standard AC PD instruments) and the acquisition configuration that resulted in being different with respect to the standard AC conditions. Moreover, a database of known defects was started. In addition, trigger-based equipment was prototyped and validated in order to localize the source on a short cable through partial discharge signals.
Monitoring System Design: The listed activities allowed us to start the design of the architecture and the requirements for the monitoring system, which is currently under development.
Life and Reliability Model: A life and reliability model of HVDC cables has been developed for both constant electrothermal stress and periodic load cycles, as well as voltage transients like Voltage Polarity Reversals and Temporary Overvoltages. A procedure for life-based geometric design of HVDC cables has been set up for both constant and time-varying electrothermal stress. A Bipolar Charge Transport (BCT) model for charge carrier injection and transport in the insulation has been developed, and the algorithm for BCT model parameter optimization from space charge measurements done in WP1 has been set forth and applied to SoA (State of the Art) DC-XLPE under different values and polarities of the applied electric field. A deeper insight into macroscopic conductivity models has been gained by fitting 5 different literature models for conductivity from the literature to conductivity measurements vs. field and temperature. The effect of insulation volume enlargement from small specimens to large cables has been addressed using an ad hoc literature formula for HVDC cables working under different loads. Tools for the inter-connection pre-fault monitoring data vs. aging phenomena have also been set up.
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 blend has been achieved at 300+ kg scale, yielding materials for mini-cable and HVDC cable prototype production in NEWGEN. Progress in Extrusion Technologies for HVDC Cables: Extrusion technologies for HVDC (High Voltage Direct Current) cables have advanced with the addition of a new triple crosshead with a spiral insulation distributor, dedicated to thermoplastic insulation. This is a new addition to the existing product portfolio.
Innovations in Monitoring Partial Discharge Phenomena: 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.
Innovations in Monitoring Partial Discharge Phenomena: 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.