The article is focused on a load angle measurement and estimation in excitation control systems of synchronous generator. Load angle is measured by digital encoder. The estimation method is based on synchronous generator parameters given by the corresponding voltage-current vector diagram. The estimation results were compared with the measured ones. The estimation method gives satisfactory accuracy for load angles less then 120°°el. Load angle control in excitation systems improves the stability of a synchronous generator in capacitive operating mode.