in CONVERGENCE. In most cases, reducing the entire network to a frequency equivalent is not required for harmonic studies because the simulation time remains short for the entire detailed circuit. The final harmonic study reflects the results of almost 1,000 simulations that correspond to different network topologies and configurations for filter switches associated with line-commutated converters (LCCs). The overall results are summarized as surfaces in the RX plan-where R is the real part of the impedance and X the imaginary part. Figure 3 shows an example of the results at a given substation. figure 2. The French 400-kV grid after a CIM import in the EMTP. Background Harmonic Analysis for an Offshore Wind Farm Connection 52 IEEE power & energy magazine The first set of offshore wind farms will connect to the 225-kV grid with ac cables insulated with cross-linked polyethylene. Since these cables are 38-60 km long, they inject a high amount of reactive power. Onshore installation of shunt reactors limits the reactive power injected to the grid. Consequently, steady-state voltages are higher at the offshore delivery point than at the onshore connection point, which requires designing the booster transformer to control the voltage on the connections independently of the grid voltage. Figure 4 shows a singleline diagram of a generic connection. RTE's assessment of harmonic issues for wind farm connections consists of both on-site measurements and simulations with EMTP. Harmonic measurements assess the level of harmonic voltages currently existing on the grid. Measurements occur for several weeks at substations where wind farms are going to be connected. Then, simulations determine the amplification of these harmonics due to the connections of the wind farms. Since background harmonic amplification is a steadystate phenomenon, it is satisfactory to perform simulations only in steady state. For such studies, frequency-scan simulations calculate steady-state operation at each frequency. may/june 2019