You've asked a rather broad question. There is a wide rage of standards required to calibrated what I normally refer to as "Panel/Switchboard Meters". Perhaps one of the better general purpose standards that would cover a lot of them is a Fluke 5500A calibrator. There is a newer model Fluke calibrator that has a higher current range. And so as not to appear to be selling calibrators, Datron also makes an equivalent. For higher current and power ranges of wattmeters, etc, Rotek, I believe is a brand name well known for high power calibrations.
For doing voltmeters, ammeters, the methods are pretty simple. But for doing wattmeters/varmeters, Phase meters, etc, you'll need either a calibrator with two sets of outputs that are phase locked, or you will need two calibrators that can be phase locked together. As for procedures/methodology, some of the three-phase meters get pretty complicated, and you will need detailed methods for the connections.
I don't know if this fully answered your question. If not, please feel free to email me, and I'll be happy to try.