The fire broke out around 11:00 p.m. at the West Park Apartments located on the 4400 block of Holden Street.
Investigators say a cat got trapped in a basement transformer causing it to short circuit, sparking the blaze and knocking out power.
The fire was placed under control around 11:45 p.m. in one of three Philadelphia Housing Authority apartment buildings located at the scene.
At first, all three buildings were without power, but crews quickly restored power in two of the buildings.
At least 85 adults and 45 children in the third building were without power.
They were transported to West Philadelphia High School where a temporary shelter was set up.
Officials say they are hoping to have a temporary generator in place by about 8:00 Monday morning to restore power and allow the residents to return to the building.
There were no reports of any injuries.