Abstract: The disclosure is generally directed to reactance modules or DSRs (30) that may be mounted on a power transmission line (16) of a power transmission system (400). A DSR (30) may be configured in a bypass mode or in an injection mode (where reactance is injected into the corresponding line (16)). Multiple DSRs (30) installed on a power line section (18) define an array (410) and have a dedicated controller (440). Such an array (410) and controller (440) may be installed on a number of different power line sections (18). The controller (440) for each array (410) may communicate with a DSR server (420), which in turn may communicate with a utility-side control system (430). Each DSR (30) may incorporate one or more features directed to core (50) configurations and assembly, communications, modal configuration control, fault protection, EMI shielding, DSR (30) assembly, and DSR (30) installation.