This is another platforming adventure into the sewers. This mission is most notable for the difficulty in getting into the sewer. There are mobs of Reapers around the objective, including a turret truck that has the manhole in its sights. Your best bet is to enter the area on top of the train tracks. Keep moving to avoid fire from the rooftops and take out the few Reapers that are on the tracks. When you get over top of the turret truck, you can fire on the exposed hood without exposing yourself to the machine gun. After you blow up the truck, jump down and hurry into the sewer.
Once in the sewer, the transformer is only a few hops away and, after re-energizing it, you get the Induction Grind ability, which allows you to grind power cables in areas of the city where power has been restored and ride the rails (grind the train tracks).
You'll put your new-found ability to instant use, grinding over cables and taking down a few Reapers along the way. Try to pick off the Reapers from long range rather than grinding directly into them. After a few twists and turns – there's only ever one way to go down here – you'll reach the substation and power another section of the city.