# Observations about Propagation, Attenuation, and Radiation of EMI from HVDC Converter Stations
###### Abstract  
The electromagnetic interference (EMI) generated by switching operations within high-voltage DC (HVDC) converter stations is an issue that has been addressed by CIGRE, and methods to manage EMI should be considered in the design phase using electromagnetic modeling techniques. It is shown that the methods of the moments-based techniques that have been used in many previous studies may not be sufficient. Here, a finite-difference time-domain method is used to study the properties of single switching events using a realistic model of an HVDC converter station with a special emphasis on determining the impact of the valve hall on shielding EMI. It is shown that the valve hall does not confine high-frequency electromagnetic fields to the valve hall; rather, it delays them from exiting through bushings in the wall and spreads them out in time. Further, it is shown that incorporating electromagnetic absorbing material into the valve hall's design can significantly reduce EMI outside the converter station. HVDC; converter station; valve hall; EMI; RFI; FDTD; MoM +
Footnote †: journal: Applied  
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Footnote 1: email: _Applied_  
Footnote †: journal: Applied  
switching speed will limit the frequencies of interest to below approximately 30 MHz. This assumption has been validated by a statement in a later CIGRE paper [3]. \"Above 30 MHz it is not possible to distinguish the level generated by the installation from the background noise level\". Along with proposing EMI limits, the CIGRE Guide has described the methods to be used to measure EMI (e.g., antenna and detector types, including their peak and quasi-peak) [1]. In addition, guidance is provided for interpreting measurements, since EMI from other sources generally exists and must be separated from that generated by HVDC converter stations [1]. Generally, when HVDC converter station vendors propose equipment for these facilities, they are required to predict its EMI and will want to ensure that the EMI meets CIGRE limits at this stage. Further, since these stations are expensive and time-consuming to construct or modify, modeling EMI is required to reduce the cost and time needed to meet EMI limits. Given this background, a considerable amount of research has been published in the area of the electromagnetic modeling of HVDC converter stations. As a necessity, these models utilize numerical modeling techniques, given the complexity of the stations. In fact, in Sec. 6.1 of the CIGRE Guide, it is noted that [1], \"Describing an electromagnetic complex environment like the one of an electric substation is very complicated not only for the model itself, but mainly for the difficulty in knowing, even with rough precision, all the sources of electromagnetic field contained inside the fence circumscribing the area relevant to the substation...\"  
There are three components to constructing a model. The first is to define the fundamental source(s) of the EMI. The second is to construct a model that accounts for the propagation of EMI currents throughout the HVDC converter station. This model will account for various components such as transformers, the smoothing reactor, and the filters (if any). Appropriate techniques (e.g., circuit theory, transmission line theory, and full-wave theory) are used depending on the distances involved relative to the appropriate wavelength. Finally, the resulting currents can be used for calculating the electric and magnetic fields in the vicinity of the HVDC converter station. This model should include the effect of shielding provided by the valve hall. The specific characteristics of EMI sources within a station are not the subject of this paper because they are usually proprietary to a given manufacturer. Rather, the disposition of the electromagnetic energy generated by these sources will be carefully examined. (For a transient source voltage with no DC component, energy inserted into the non-radiating near field is reabsorbed by the source by the time the transient voltage ends. What remains is the radiated field.)