You have to find a NPC, named Alison.
When to start
After Priority: Palaven
“A technician at Purgatory on the Citadel needs an improved power grid to keep things running.
Find schematics for a new power grid and deliver them.”
Alliance Fifth Fleet War Asset
This quest can be completed while playing the Cerberus Attack N7 mission.
You will get the Improved Power Grid and all you have to do, is to return to Alison to finish the mission and collect your reward.
Next Citadel mission: Heating Unit Stabilizers.