What's the name of this type of connector used for high current
The name of this type of connector seems to be single-conductor, pin and sleeve, connector or plug. Information is available online for similar systems by Crouse-Hinds called Cam-Lok and Pos-Lok. Crouse-Hinds is a subsidiary of Cooper Industries which is a subsidiary of Eaton Corp. Other possible manufacturers or brands include Legrand, Killark, Hubbell and Leviton. These items may not be very widely marketed. Different variations of a given connector system may be used by individual equipment manufacturers for specific types of equipment.

The equipment referenced in the question seems to be utility power distribution test equipment. Other types of equipment or industries that may each use a different variation of the same thing may include welders, watercraft shore power, aircraft ground power, theatrical event power, industrial test power and others. Even if more than one equipment OEM uses exactly the same plug type, the plug manufacturers may not sell the the plugs through distribution channels.