According to a supervisor on site, Con Edison needs to repair a failure in an underground electric transmission cable running beneath Dahill Avenue. But because the insulating oil that fills the cable is pressurized, the oil has to be frozen at two points, one on each side of the failure, so that the cable can be sliced open and fixed without all the oil rushing toward the cut. At the "freeze pit" pictured above, as well as at another similar structure located down the road on the other side of the failure, liquid nitrogen (I believe) is being used to freeze the oil in the cable.
Day 813
Con Ed freezer shack
March 22nd, 2014
You did a great job with your description. This is highly technical work done by a handful of trained workers. Picture high voltage (138,000 volt) wires in a tube/pipe under a street. Those wires make a lot of heat to power large sections of the city. In order to cool them, oil is pumped at high pressure around the wires picking up the heat. If the wire/conductor has a fault (short circuit) it must be repaired. You can’t remove the oil because it is needed to keep the rest of the wire in operating shape and there is too much of it. So you do a freeze pit, make the Wire repair and return the street back to normal in a few days.