So a VAX system huh? Cool. This was from the cover of a handbook I came across some time ago.
It pertained to the equipment in the foreground - a system an electric utility could deploy to manage interruptible loads (air conditioners, water heaters, etc.) during system peaks, as well as the ability to remotely read meters, all using a 9-12kHz carrier overlaid on the 60Hz power lines. The large cabinet is the transceiver installed in the substation, and which tied into the distribution system using the coupler box next to it, and in the foreground is a load controller with two different kinds of remotely readable electric meters.
The minicomputer would have been in the main office and communicated with the transceivers to transmit load control commands and ping the meters for the readings. I would imagine as microcomputers became more popular in the late 1980s, the office side of the system would have evolved to reside on one or two PCs instead.