Substation levels

The question “What’s the difference between bay ,process and station level, why and when we use them?” was asked. My response was:

@Mudassir, if you have access to 61850 standards then the best place to get the formal definitions is from IEC 61850-1. The station, bay and process levels are defined in section 6.2, with Figure 2 showing it graphically. To extract the definitions:

  • Process level devices are typically remote I/Os, intelligent sensors and actuators
  • Bay level devices consist of control, protection or monitoring units per bay.
  • Station level devices consist of the station computer with a database, the operator’s workplace, interfaces for remote communication, etc

Basically the process level is where the control system interfaces with tangible hardware: current transformers, isolators/disconnectors, circuit breakers, transformer temperature sensors and so forth.

The bay level is where the substation control system looks after a piece of plant as a whole (e.g. transformer, feeder), and as Grant mentions, an understanding of the intricacies here will require an understanding of power systems control and protection.

The IT and telecoms equipment in a substation sits at the station level, but still requires power systems knowledge to understand ‘whole of station’ function like CB failure protection, bus protection, control philosophies (equipment) and how the humans will interact with the substation (remote operation or local?)

The IEC 61850 family are designed to be read in sequence. -1, then -2 and so forth. This means that you’re only getting to the nitty-gritty of GOOSE, MMS and sampled values in -8-1 and -9-2 once you’ve read about the object model, how logical nodes are used and the use of ACSI to communicate between nodes. Avoid jumping in at GOOSE/SV, otherwise you risk seeing 61850 as ‘just another protocol’. It is a system and should be thought of as such.

There are some good introductions to 61850 out there on the internet, so use your favourite web search engine and see what you can find. I’d suggest looking at the works from 2004-2008 first as this is when 61850 was kicking off and the good introductory material was published. PAC World and GE’s Protection & Control Journal (now called the Grid Modernization Journal) are well worth looking at.