On the day of accident the turbines were at working level 212 metres (696 ft). At this pressure the recommended power band for the turbines is 570–640 MW (band III) and the allowed band is 0-265 MW also (band I). Band 265–570 MW (band II) at this pressure is not recommended and output over 640 MW (band IV) is forbidden.[2] On the day of accident turbine 2 worked as the plant's power output regulator and due to this, its output power changed constantly. The turbine often operated in the band II regime which is accompanied with pulsation and strokes of water flow.