Electric field computation for HVDC GIS/GIL spacer under superimposed impulse conditions
This paper evidences the influence of different parameters on the electric field on DC spacers in GIS/GIL and thus their dielectric withstand under S/IMP tests. A notable difference in term of electric field can be observed in function of impulse polarity, load condition (with/without heating current) and insulating material’s properties. For example, an overstress of 0.3pu was obtained on spacer’s surface in case of superimposed impulse test with opposite impulse polarity, high load condition and high leakage current in gas. Contrary to AC system where the simple LI tests were enough, S/IMP tests with both impulse polarity, ZL and HL conditions are mandatory to verify the insulating performance of HVDC GIS/GIL spacer. This paper gives a better understanding of the electric field distribution in HVDC GIS/GIL and helps for the design and tests
3-phase medium frequency transformer for a 100kW 1.2kV 20kHz Dual Active Bridge converter
The article presents a three-phase Medium Frequency Transformer being a part of a 100kW 1.2kV 20kHz Dual Active Bridge DC-DC converter. The transformer design is detailed focusing on winding and core power loss calculation. The high power three-phase MFT prototype is presented. The experimental results include the transformer impedance characteristics, no load test and three-phase DAB full load test waveforms.
Cost-performance framework for the assessment of Modular Multilevel Converter in HVDC transmission applications
This article proposes a methodology of Cost-Performance Assessment (CPA) enabling the efficient cost evaluation required for the Cost-Benefit Analysis (CBA). The proposed method is applied for the Modular Multilevel Converter (MMC) in offshore wind high voltage direct current (HVDC) transmission. Thanks to the developed model, an analysis of submodule voltage rating is performed demonstrating the interest of this methodology in the evaluation of new technologies for HVDC transmission. The analysis shows that increasing the submodule (SM) voltage could lead to savings in the MMC cost and weight.
Requirements for interconnection of HVDC links with DC-DC converters
The number of high voltage direct current (HVDC) links continue to increase over the years, most of them, for offshore applications or bulk power transmission over long distances. The present paper evaluates the possible development of a direct current (dc) grid in Europe given the present, and future, HVDC links. Eight potential cases for the interconnection between close links are suggested as starting scenario for a multiterminal network. The need of a dc-dc converter and its special requirements are evaluated in function of suggested interconnections. As an example, a case study is chosen to evaluate the behavior of an interconnection between line commutated converter (LCC) and voltage source converter (VSC) link using a front-to-front (F2F) isolated converter.
Assessment of the Impact of Split Storage within Modular Multilevel Converter
This paper deals with the opportunities to introduce split storage into an MMC. The analysis is focused on the internal energy exchange to maintain the proper function of the converter by using circulating current. Analysis shows that, SM capacitor voltage ripple or semiconductors load are greatly influenced by additional circulating current injection. This study helps to design Embedded ESSs in the converter to provide new function like ancillary services for power system operation. Finally, a simulation of an MMC with ESS confirms analytical calculations.
Use of Unbalanced Insulation for the Limitation of Double-Pole Lightning Flashovers in Double Circuit HVDC Overhead Lines
Lightning studies are a critical part of any system involving overhead lines. As HVDC technologies develop, new problems and questions arise regarding the lightning performance of HVDC overhead lines. For instance, the installation of two separate HVDC circuits on the same transmission tower may become a popular alternative for the uprating of old AC lines to take advantage of the already existing Right-of-Ways. Double-pole flashovers may be particularly constraining in double circuit HVDC systems, since they could lead to the loss of both circuits at the same time due to the flashover of both poles of the same polarity having the same amplitude at all times (which is not the most likely case in AC systems). This corresponds to a 100% of loss of transmitted power, which could represent a threat for the system stability. This constitutes the main motivation for this work.