The document discusses various methods for controlling voltage in power systems. It describes how voltage control is achieved through tap changing transformers, which can control voltage within a range of +15% to -15%. Both off-load and on-load tap changing are discussed. Shunt reactors and capacitors are used to control voltage by compensating for line inductance and capacitance. Series capacitors are used on long EHV lines to reduce line inductive reactance and increase power transfer capability, but not for direct voltage regulation.