Pole pigs or distribution transformers are large transformers used in the supply of electricity to homes and industry.
They can be used to step up mains voltage to distribution potentials (15KV or so) and are rated to large currents (15-50A at the mains side). For Tesla coil use they need to be current limited, this is usually done with a large choke in the supply.
Although very robust they are very heavy.
The output from a distribution transformer is LETHAL