NGR Grounding in Alternator

Dear members,

i am in 12.5 MW,4.16KV cogen thermal power plant, we are step up the power through 16 MVA transformer to 69 KV.in 12.5 MW we are closing the NGR only at time of synchronising only, after synchronising we are opening the NGR. IN the step up transformer , the NGR is always closed condition

i want to know this is the correct procedure or not, kindly clarify this