With the Nexus meters we mostly provide readings in secondary values. There are 2 ways to get to the primary values.
You can multiply the secondary values by the CT and PT ratios. For voltage and current, you would have your system multiply by the PT ratio and CT ratio respectively. For example, if you hat a CT ratio of 1200/5 the ratio is 240. So, if you had 3.5A in the secondary IA register the primary current is 3.5X240 or 840A. For energy you need to multiply by both CT and PT ratio.
The second method is to use the Custom Modbus mapping provided in the Nexus meters. Go into the profile for the meter and under general settings you will find a tab for Custom Modbus Map. You can define pretty much anything the meter reads or calculates in that map. You can use this to load Primary values into custom registers and then read Primary values.