In which regulation modes do OEL and UEL operate on the D510C? FAQ Writer August 08, 2018 08:15 Updated Follow OEL : Over Excitation Limitation : operates whatever the regulation mode UEL : Under Excitation Limitation : only operates in PF or kVAR regulation mode to avoid any unstability in case of to too high level of capacitive laod in prallel operation. Related articles What should I do if there is no reaction observed when adjusting the external signal through the D510C inputs? Why is the D510C unable to sustain long duration LVRT? What are the differences between the versions of R449: R449 E, R449 F1 & R449 F2? How to handle thermal drift on the D510C?