Avoiding GGIO

The real benefit of using a function specific logical node (e.g. PTRC, PDIF etc) is that the LN conveys a lot of semantic information.

If you use GGIO you need to maintain a parallel set of document that describe the purpose of each GGIO. This is really no benefit over DNP3 or Modbus points. If I am subscribing to messages then I know that I have the transduced power (MW) value when I connect CVMMXN1.MX.Watt.mag or PriFouMMXU1.MX.TotW. An analogue GGIO simply doesn’t do this.

Which has more meaning: T3WPDIF1.ST.Op or BOUT_GGIO1.ST.Ind.stVal? I can tell immediately that I've connected the transformer differential trip with the 'proper' LN without needing to refer to anything else. The devices don't care what is subscribed to in the SCD file, but it sure helps reduce the chance of the human making a mistake.

These data attributes come from a real IEC 61860 system. The only reason I used GGIO for outputs is that they came from an RTDS that treats GOOSE output as a binary output card. The IEDs all supported 'real' LNs in their published GOOSE datasets. Making sure I had the right GGIO when setting up IED subscriptions was a pain in the neck—setting up the RTDS subscriptions was very easy by comparison.

IEC 61850 is all about systems, not simply communications between devices.