Redefine term "switchyard" and add term "substation"

[amanda-wein]

Description of the issue

The term OEO_00020009, "switchyard", is incorrectly defined as "an electricity grid component that connects different levels of voltage." This is not a switchyard, but a substation (at least in my experience, and also confirmed with a quick Google search to make sure I'm remembering correctly). The key difference between the two is that a switchyard contains the switchgear necessary for deenergizing some circuits and swapping load over to other circuits, usually in the event of a power outage or for scheduled maintenance. A substation contains some of this sort of switchgear, but it also contains transformers for stepping voltage from a higher level to a lower level, and that voltage transformation is the substation's primary purpose.

Ideas of solution

Redefine "switchyard" and add a new term "substation" with definitions along the lines of:

• A switchyard is an electricity grid component that operates at a single voltage level and contains switchgear for reconfiguring the circuits of a power grid. (can also be referred to as a "switching station")
• A substation is an electricity grid component that operates at two or more voltage levels and contains both transformers for stepping electricity between the voltage levels and switchgear for reconfiguring the circuits of a power grid.

I'm not sure how much detail should go into the definitions. You could perhaps also expand on this with subclasses for the substation term:

• A transmission substation is a substation that transforms voltage from one transmission level to another transmission level.
• A distribution substation is a substation that transforms voltage from transmission levels to distribution levels. OR A distribution substation is a substation that connects the transmission system to the distribution system.

However, all of my experience working with power grids comes from the US. I'm not sure if the "transmission substation" and "distribution substation" definitions I've proposed hold true for Germany's power grid, since Germany defines voltage levels differently than the US does, with a different dividing line between "transmission" voltages and "distribution" voltages:

Germany (source: https://www.smard.de/page/en/wiki-article/5884/214026)

	Voltage	System
Ultra High Voltage	n/a	n/a
Extra High Voltage	220kV to 380kV	transmission
High Voltage	110kV	interregional distribution
Medium Voltage	10kV to 30kV	regional distribution
Low Voltage	400V	local distribution

USA (source: https://www.generatorsource.com/Articles/Generator-Info/High-Medium-and-Low-Voltage-Differences.aspx and my personal experience working as a power engineer for US utility companies)

	Voltage	System
Ultra High Voltage	> 765kV	transmission
Extra High Voltage	345kV to 765kV	transmission
High Voltage	115kV to 230kV	transmission
Medium Voltage	2.4kV to 69kV	69kV is transmission. < 69kV is distribution.
Low Voltage	240 to 600V	distribution

Workflow checklist

• [x] I discussed the issue with someone else than me before working on a solution
• [x] I already read the latest version of the workflow for this repository
• [x] The goal of this ontology is clear to me

I am aware that

• [x] every entry in the ontology should have a definition
• [x] classes should arise from concepts rather than from words