Offshore wind is set to be competitive with fossil fuels within the next decade. The International Energy Agency estimates in its Stated Policy Scenario from 2019 that the Levelized cost of energy (LCoE) from offshore wind will decrease 40 % by 2030, where transmission infrastructure accounts for one-third of the costs. The modular high-voltage direct current (ModHVDC) generator connects converters in a series of modules for a segmented HVDC generator, which limits the number of conversion steps in comparison to a typical offshore wind farm. This paper aims to validate the thermal design proposal for ModHVDC generator. It is especially important for larger generators utilised in wind- or hydro-power applications, as replacing components is complex, time-consuming, and expensive. Thermal management in electric machines is important, as poor heat dissipation leads to a loss of efficiency and can severely reduce the expected lifetime of the machine. In this paper, an analytical approach to determine the heat loss coefficients for the machine is deduced. Magnet, copper, and iron losses are provided to estimate the heat generated in different parts of the machine. Two different core loss calculation methods are used. The analysis shows that the temperature does not exceed critical levels for both methods. The end results prove that the design solution is viable with the use of forced convection for cooling in the air gap with maximum temperatures of 66.8 °C in the permanent magnets and rotor.  

This review covers the multidisciplinary conundrum shaping hydropower development within the broader energy transition. Classical hydropower generation facilities are transformed toward more flexible operations to adapt and facilitate the integration of intermittent renewable energy sources. As a result, their operating modes will be far from their designed rated point. This review explores this paradigm shift in three perspectives: machine design considerations, power plant operation, and transmission system operator (TSO) mandates. It also present the implementation of innovative analysis techniques to give a deeper understanding of the energy transition's associated challenges and its possible solutions. In particular, machine design challenges include magnetic saturation, efficiency estimation and mechanical wear and tear. Moreover, power plant operators needs to consider the effects of flexible power production caused by variable renewable, while in contrast grid regulators needs to strengthen reactive power mandates and system-bearing services to ensure stability.

Over the last decade, large hydropower plants have shifted their operational regimes from nominal conditions to more diversified load cycles owing to the increasing share of intermittent renewables that have necessitated more flexible hydropower operations. However, increased load variability has made the hydrogenerator efficiency a more important economic metric. This paper proposes a method for redesigning the hydrogenerator rotor pole and refurbishing the field winding to enhance economic performance. The effectiveness of these changes is evaluated by estimating the levelized cost of non-optimal operation across various operating regimes. We present two alternative rotor redesigns for a 103-MVA hydrogenerator that indicates significant economic benefits for a diverse set of load cycles. Generally, the net present value of these benefits is found to be four to six times greater than the material costs incurred during the refurbishment phase.

Worldwide wind power capacity jumped from 7.5GW in 1997 to 564GW by 2018, according to IRENA. Many regions of the world have strong wind speeds, but the best locations for generating wind power are often remote, where offshore wind power offers tremendous potential. This paper presents a concept to remove the use of offshore platforms/substations, constituting the energy conditioning element for high voltage direct current (HVDC) transmission. Instead, it connects converters in a series of modules for a segmented HVDC generator, which limits the number of conversion steps. Our work focuses on the impact of segmentation on loss and is validated numerically using finite element analysis (FEA) and analytical solutions. The machine’s geometry, design constraints, design procedure, loss calculations, and numerical analysis are included. Three different methods are presented and used to determine the core losses. The paper highlights the increase in core losses due to airgap segmentation. We show that Zhang’s method yield the largest deviation in the loss calculations, i.e., 15.812%, 16.410% and 15.894% increase in core losses for 10, 20 and 30 mm segment airgaps, respectively.

As a result of the worldwide energy transition, reactive power generation has started to become a more scarce resource in the power grid. Until recently, reactive power has been an auxiliary grid service that classical power generation facilities have provided without necessarily allocating any cost for this valuable service. In this paper, a new approach for predicting the additional costs of reactive power services delivered by large hydrogenerators is proposed. We derive the optimal reactive power with minimal losses as a function of the active power level within the generator’s capability diagram. This pathway can then be used to calculate additional losses from operational regimes deviating from the optimal reactive power for each active power level. To back up the analysis, a dedicated population study was handpicked consisting of four real-world generators scaled in terms of power rating, i.e., 15 MVA, 47 MVA, 103 MVA, and 160 MVA. The objective was to identify how the optimal reactive power scale from smaller to larger MVA-sized generators. Moreover, a sensitivity analysis explores the link between the standard parameters, the stator losses, the rotor losses, the optimal reactive power, and the optimal efficiency. We find the ratio between the rotor and stator losses as the determining factor. Finally, the operational pathway introduces a new way to allocate the power producer’s cost associated with their reactive power services and can be used to justify potential profit for this service, especially considering that the intermittent reactive power needs are projected to increase in the future.