# Observations about Propagation, Attenuation, and Radiation of EMI from HVDC Converter Stations
## 3 Results
### The Finite-Difference Time-Domain Method: Initial Insights from Simple Geometries
Rather, if one integrates the square of the field over time, the overall value will be higher when the hall is present due to the way in which it hinders the radiation of energy in all directions except via the transmission lines that pass out of the hall. Because there is no loss present within the valve hall, the only place energy can go after it is introduced into the valve hall is out along the conductors that pass through the valve hall walls, i.e., along the transmission lines out of the hall. At these frequencies, these lines serve as antennas which then radiate fields into the surrounding environment (as will be considered below). Instead of a component of the electric field, consider the current on a conductor measured both inside and outside the valve hall. The current is obtained by taking the line integral of the magnetic field around the conductor at the desired measurement point. The current was calculated on the same line on which the source exists (the northern-most line exiting the valve hall to the right in Figure 1a). The inside and outside measurement points are each 2 m from the wall (with one being inside the valve hall and the other being in the DC hall). Temporal plots of the currents at these points reveal a difference in the arrival time of fluctuations, which is consistent with the different locations of the observation points. There are some other differences in the currents, but these are relatively minor. Rather than showing a temporal plot, Figure 4a shows the log magnitude of the normalized spectrum of the currents when the valve hall is present. Figure 4b is the same scenario as Figure 4a, except the valve hall has been removed. Although there are some slight differences in the features observed in Figures 3 and 4, overall, the results in Figure 4 serve to confirm the statement made in connection to the measurement of the electric field: the valve hall does practically nothing in terms of confining high-frequency energy to the interior of the valve hall. One could say that the hall serves to redirect energy while not eliminating it (i.e., delaying energy's eventual escape from the hall). Once a current has been established on a line within the valve hall, if that line exits the valve hall, the current found outside the hall will be nearly the same as that inside. Having established that the valve hall does little in terms of reducing the ultimate escape of high-frequency currents and fields, attention is turned to measurements more aligned with those related to compliance. CIGRE [1] is frequently concerned with the fields that exist \"200 m from the closest active part of the station\". The computational domain was extended 200 m (400 cells) in the \(y\) direction (simulations of 65, 536 time steps now required approximately five and half hours to complete on the Apple Mac Studio mentioned before) and the field was measured at several observation points that were 200 m \"south\" of the southern-most valve hall wall depicted in Figure 1(a., 400 cells away from the valve hall wall in the \(y\) direction). Recall that the entire computational domain sits atop a perfectly conducting ground plane. All components of the electric and magnetic fields were measured at 15 different locations with varying \(x\) and \(z\) values. The observation points were separated 15 m in \(x\) and had vertical displacements (\(z\) values) either 2, 3, or 4 m above the ground plane. In the discussion that follows, any, or all, of these points could have been selected and would lead to the same observations. For the sake of concreteness, however, an observation point was selected that is 20.5 m to the \"west\" of the western-most valve hall wall (i.e., the one leading to the AC yard), 200 m south of the southern-most wall, and 2 m above the ground plane. Figure 4: The log magnitude of the normalized spectrum of the current measured at two points along the top-most line from the valve hall to the DC hall. (**a**) The hall is present. (**b**) The hall has been removed.