INA-Industrija nafte, d.d. (INA, d.d.) is a medium-sized European oil company and a leading company in Croatian oil business. A fuel refinery plant INA RNR located in Urinj has three generator sets (10MVA, 25MVA, 26 MVA) to ensure reliable power supply to important elements of the oil refinery process and prevent their unplanned and sudden shutdown. However, disturbances generated within transmission or distribution network, especially during violent summer storms, provoke negative impact and failures in plant’s power system.

Disturbance influence on frequency drives powering critical 6.6 kV and 0.4 kV loads has been assessed with 6 SterPMU devices equipped with continuous waveform recording feature. Problems with the stability of generation control revealed with the help of reference PMUs at transmission and distribution networks.