IEC 61869-1 is the international foundational standard for instrument transformers
Same as above: or your local national standards body. Expect to pay 250–300 CHF per part. iec 618691 pdf
IEC 61850 is the cornerstone standard for . It defines how Intelligent Electronic Devices (IEDs) – such as protection relays, bay controllers, and circuit breaker monitors – communicate with each other over an Ethernet network. IEC 61869-1 is the international foundational standard for