Good afternoon, at the moment we are commissioning a GE frame 9e gas turbine, and during the crank mode (purge of GT), the turbine speed fluctuates from 475 to 541 rpm. Contractors insist that this is normal, we tell them the speed is not stable during gt purge (crank mode)(475-541rmp) and it is not ok. Could you please help us if this is normal or not and how to prove it to the contractor. Also, when the speed reaches 541 rpm, the 20tu valve energizes and relieves pressure. when the speed reaches 475 rpm the valve closes and the speed increase begins, and so the speed of the turbine floats from 475-541. Are there any documents that describe this in detail. URGENT!!!