On Google, look up Solid state voltage regulator. especially look up ABB PCS100 AVC, a solid state voltage regulator available to over 3 MVA. One of my customers uses it on the tertiary of an auto-transformer that has a reactor as well as station servce. When the reactor switches in and out, there is an instantaneous 10% drop in voltage. The station service is on the regulator, and does see a blip.