MTX (merging units) are devices connecting the secondary circuits of the power station with IED executive units, e.g. UTX3.x.
These are precise and very fast devices that sample analog voltages and currents from the electromagnetic outputs of PT and CT transformers, which are sent in the form of digital SV samples (sampled value) in accordance with the IEC 61850-9-2LE standard to server units.
The mapping of the field switches and their control by the IED server units is based on the transmission of GOOSE packets in accordance with IEC61850-8-1.