Fox 6 has the story. From it …
Officials were called to Appleton Electric in South Milwaukee on Sunday, June 23rd in response to reports of explosions.
It happened around 12:30 p.m. at the Appleton Electric building next to Grant Park. Officials say the “explosions” were caused by a transformer on the building that shorted out.
Officials say the flames quickly went out on their own.
No one was hurt, and damage was minimal.
I’ll keep you posted if I learn more.
South Milwaukee Blog 
My husband works there, we haven’t heard anything