The purpose of this paper is summarize the state-ofknowledge of the effects of power system harmonics on equipment. The general mechanisms presented are thermal overloading, disruption, and dielectric stressing. Quantitative effects are presented o r referenced whenever possible. However, many of the effects are can only be qualitatively described. The equipment considered are adjustable speed

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possible to place it in standard shipping containers. If this power-rating limit is exceeded, the transformer is subject to significant additional costs due to transportation. Consequently, a saturation of the large-scale PV plants' cost decrease is expected in the near future.In order to continue reducing the cost of large-scale PV plants, other alternatives have to be investigated. Mediumvoltage cascaded H-bridge conversion systems, MV CHB, and medium voltage modular multilevel conversion systems, MV MMC, [2]-[4] have appeared as potential solutions. They consist of conversion stages whose output is connected in series, generating in medium voltage (MV). The conventional step-up low-frequency transformer is then substituted by a high-frequency transformer in each conversion stage. LF transformers reduce the volume and therefore the cost of the transformer stage [5]. Moreover, the series connection of converters in these conversion systems enables the reduction of the power rating of each individual conversion stage while maintaining the power rating of the conversion structure. Consequently, a reduction of the number of PV modules connected to each conversion stage is achieved. This reduces the dc-wiring length, as the conversion stage is located closer to the PV modules, reducing the dc-wiring cost. In addition, as voltage is stepped up at the output of the conversion stage, current is stepped down, allowing a lower cross section in the ac-wiring than in the dc-wiring. Again, this also reduces the wiring cost. Furthermore, the series connection of conversion stages makes it possible to obtain a multilevel output voltage, reducing the grid current harmonics and therefore the cost of the required output line-filter. Fig. 1. Traditional large-scale PV plant configuration

and by the Public University of Navarre through a doctoral scholarship. The proposed topology is patent pending (document WO2019155109A1).