Firefighters were called to the scene in Mushroom St, behind Regent Street, at about 9.20am today (Sunday).
The substation, close to PureGym, which also serves Aldi, Poundland and other businesses in Regent Street, was damaged in the fire.
Crews extinguished the flames and Northern Powergrid engineers are now on route to the scene, according to a spokesman for West Yorkshire Fire and Rescue Service.
They are expected to set up a temporary generator to restore the power supply until the substation can be fixed.
The spokesman said the substation was damaged after a fridge, placed next to it, was set alight.