So why did it take so long for the process bus to attract the attention of the industry? Well, there were several reasons; to cover them all would be a topic for a history article. To summarize - process bus, in particular sampled value communication, was mainly driven by manufacturers of non-conventional instrument transformers (significant savings were expected.) On the other side, this was not a huge market in Europe, where mainly retrofit substations were build, and relay manufacturers were not interested in supporting such interface. And last but not least, for the customers at that time it was pretty suspicious to trust communication for protection.