Add new classes to describe different voltage levels of the energy grid

[Ludee]

Description of the issue

From #1828 and oeo-dev 89

It should be possible to differentiate the different voltage levels:

• High Voltage
• Low Voltage

And the type of network system:

• Transmission system
• Distribution System

Connecting terms would be:

• TSO
• DSO

Ideas of solution

Part of #1828

Workflow checklist

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

I am aware that

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

[stap-m]

And the type of network system:

• Transmission system
• Distribution System

These should become subclasses of power system. In oeo-dev 89 we had the idea of adding a power distribution function and a power transmission function to distinguish the power systems by their purpose.
Add transmission network and distribution network as alternative labels?!

[UStucky]

Comment on #1828 (comment) (@koubaa-hmc) and #1828 (comment) (@madbkr):
The electricity distribution system cannot be a subclass of energy system because it is a part of the power system (subclass of energy system). It is not identical with the power system or with any kind of complete power system.
In Germany, the highest voltage level is the level of the transmission system and it depends if and which 2nd level part of the grid is counted in transmission or in distribution system

Comment on #1828 (comment) (@stap-m)
This comment refers to the question if energy distribution system component is equivalent to grid component.

1. electricity distribution system component is more specific because the electricity distribution system is not the whole grid (I suppose grid is equivalent to power system or to transmission + distribution system together as parts of the power system?)
2. Since cables have been mentioned; in my opinion, it is problematic to have electrical devic-es/equipment as subclass of grid component. E.g. cable cannot be a subclass of it. Cables exist independently from grid components.
   And, grid component is more a role than a class so at least a further subclassing will always be problematic. It is more like a grid (or power system?) has a relation to devices/equipment (e.g. cables) which are their components: "grid" "has component" "cable"

Comments on #1960 (comment) (@Ludee):
I think we should at least introduce the terminology used in Germany, defined by DIN norms (accord-ing to https://de.wikipedia.org/wiki/Hochspannung)
Note that other countries may have a different mapping of voltage levels to network levels (transmis-sion system TS, distribution system DS) (I do not know if the term "network level" is correct as the generic term for TS and DS, but "network" is alternatively used instead of system in the various terms we have so far.)
Voltage levels Germany:
• low voltage (230/400 V up to 1kV)
• medium voltage (10 kV up to 35 kV)
• high voltage (110 kV)
• extra high voltage (220 kV, 380 kV)
TS is extra high, the others are DS (typically)
E.g. USA: there is an ultra high voltage level beyond 1 MV

Comment on #1960 (comment) (@stap-m):
Definition of power system: "A power system is an energy system covering the generation, transpor-tation, distribution and consumption of electrical energy."
Thus, TS and DS both cannot be subclasses since they do not include generation, consumption, and distribution respectively transport.

[stap-m]

Comment on #1828 (comment) (@koubaa-hmc) and #1828 (comment) (@madbkr):
The electricity distribution system cannot be a subclass of energy system because it is a part of the power system (subclass of energy system). It is not identical with the power system or with any kind of complete power system.
In Germany, the highest voltage level is the level of the transmission system and it depends if and which 2nd level part of the grid is counted in transmission or in distribution system

Thanks for the clarification of the part of relation @UStucky I also very much agree that there should be a grid component role. Based on your comments, the ontological model could look like this (not yet taking into accout the voltage levels):

[amanda-wein]

Adding this here from issue #1975, since it's also relevant to this issue: Here's some information regarding Germany/US voltage level differences.

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

[UStucky]

The 400 V low voltage are for all three phases (Drehstrom) between any two conductors; 230 V is from any conductor out of the three to ground wire

[Ludee]

The grid component role looks good. Thanks @stap-m
The roles transmission grid role and distribution grid role
with subclasses interregional distribution, regional distribution and local distribution cover all system roles.

The artificial object can be the existing electricity grid OEO_00000143. (alt label: Stromnetz, electricity network)
voltage level are very useful, thanks @amanda-wein
What relation is this? And are the level classes or instances?

And I am not sure how to define the voltage.
As far as I remember some are "lists" like "220 kV" or "380 kV".
And some are ranges like "10kV to 30kV".
Can someone clarify this?

The related terms cable or electricity cable must be considered as well. @UStucky
With underground cable (Erdkabel) and overhead cable (Freileitung).
And the related topic substation. (Trafostation)

That are quite a lot of new terms and needed definitions. 👀

[amanda-wein]

Some voltages will be ranges, and some will be single values. Would it make sense to define classes ultra high voltage, extra high voltage, high voltage etc., and for each of those classes, specify the precise voltages and the system (electricity transmission system or electricity distribution system) that it falls under? That does get a bit complicated with US medium voltage being both transmission and distribution, though.

Voltage levels might work as properties of electricity distribution system and electricity transmission system, since these terms are differentiated from each other primarily by their voltage levels.

In general, all types of equipment can be found operating at all voltage levels. But if we're talking about one specific piece of equipment in particular:

• One switchyard will operate at exactly one voltage level. (could be transmission or distribution)
• One substation will operate at at least two voltage levels. (could be all transmission, all distribution, or a mix)
• One transformer will operate at exactly two voltage levels. (could be transmission-transmission, transmission-distribution, or distribution-distribution)
• One cable (if underground) or conductor (if overhead) will operate at one voltage level.

How much detail do we think we need for this ontology regarding the physical structure of a power grid?

I can keep giving this some thought and see if I can come up with a better way to define it.

[UStucky]

I would say that voltage level is the class, the levels explicitely named so far are instances of it; German voltage levels are different instances from US voltage levels. An instance of a distribution system has 1 to n voltage levels; dto. an instance of transmission system. DS and TS in US are different instances from German DS and TS respectively.

As for the question of detail - it depends on how the domain OEO describes is defined; I think the Common INformation Model (CIM) is a good example and can guide an ontologization of the technical stuff of power grids (and other stuff, too); Link e.g.: https://zepben.github.io/evolve/docs/cim/cim100; I have some Enterprise-Architect models from a few years ago.

If we take a look at the class VoltageLevel in CIM we can find that in general the values are ranges, described by their limiting voltages (which does not exclude single valued VLs).

[Ludee]

and for each of those classes, specify the precise voltages and the system (electricity transmission system or electricity distribution system) that it falls under? That does get a bit complicated with US medium voltage being both transmission and distribution, though.

We want to implement the grid component role, so a grid level has transmission grid role and/or distribution grid role.

I think we should start at the top concepts:
OEO:power system A power system is an energy system covering the generation, transportation, distribution and consumption of electrical energy. (DE: Energieversorgung/Elektrisch)
Missing relation to:

OEO:electricity grid An electricity grid is a supply grid that transports and distributes electrical energy / electricity. (DE: Stromnetz)

NEW:
An electricity grid has one ore more grid level: A grid level is part of an electricity grid and is characterized by its voltage level and grid component role and its geographic coverage.
(DE: Netzebene)

NEW:
A voltage level is a characteristic (?) of a grid level. Extend definition (DE: Spannungsebene)

electricity grid has part some electricity grid component: An electricity grid component is a grid component that is part of an electricity grid.

• link / OEO:power line A power line is a grid component link that is an uninterrupted transmission system between two nodes in an electricity grid. (DE: Stromleitung)
• OEO:switchyard: A switchyard is an electricity grid component that connects different levels of voltage (@amanda-wein I would follow your definition) Redefine term "switchyard" and add term "substation" #1975
• OEO:transformer: A transformer is an electricity grid component that passively transfers electrical energy from one electrical circuit to another.
• NEW: substation has part some transformer ? (similar to OEO:power plant
• OEO:power plant A power plant is an energy transformation unit consisting of power generating units and a grid component that feeds electric energy into an electric grid.
• OEO:energy storage unit An energy storage unit is a grid component that stores energy.
• OEO:grid node A grid node is a grid component of a supply grid where two or more links meet.
• Some connection to the demand/consumption: OEO:energy demand sector An energy demand sector is a sector that covers energy consumers. The grid connection of the consumer.

[UStucky]

I think we should start at the top concepts:
OEO:power system A power system is an energy system covering the generation, transportation, distribution and consumption of electrical energy. (DE: Energieversorgung/Elektrisch)
Missing relation to:

OEO:electricity grid An electricity grid is a supply grid that transports and distributes electrical energy / electricity. (DE: Stromnetz)

So, the electricity grid can only be the TS and DS part of the power system- as far as it is specified now in this discussion.

And what about "grid level"? That is a new term (regarding this discussion) - it is translated to "Spannungsebene", but that is (should be?) the voltage level. Is there a differnece? What does the geographic coverage (?) has to do with it? An electric system is rarely characterized in terms of any geography (as long as it is not relevant where some part of it is located because someone has to go out to fix something or the like).

If it comes to describing the technical power system/grid or whatever it may be called, I think it is mainly a matter of part-whole and nothing else. When I speak of a grid component, then it is just the collection of the parts of the grid. It is a relation between the grid and the entities that are parts of it. It is the property, predicate, relation, however it is called, of a grid, we can call it grid components, and the real things that are members of the collection are devices, equipment that are components of the grid.

[stap-m]

The voltage level could be modelled as quality (physical property) of grids/systems which may have in addition a role or function of distribution/tansmission (to be specified). Like this, we can decouple the voltage level and the distribution/transmittion role/fuction of a grid.

[stap-m]

• link / OEO:power line A power line is a grid component link that is an uninterrupted transmission system between two nodes in an electricity grid. (DE: Stromleitung)
• .......

As said above, the "grid components" should be classified as artificial objects. For the Arisotelian def this results in something like:
A power line is an artificial object that is a link in an uninterrupted transmission system between two nodes. We could/should extend the def with a sentence like It has the grid component role./ It is usually used as grid component. / ...

This holds for all grid components.

[stap-m]

A question: is the electricity distribution system the same as the electricity distribution grid? Or is the grid part of the system?

[stap-m]

NEW:
An electricity grid has one ore more grid level: A grid level is part of an electricity grid and is characterized by its voltage level and grid component role and its geographic coverage.
(DE: Netzebene)

As far as I understand "Netzebenen", they are mainly labels for certain types of grids (with a certain voltage level, in a certain region (DE, AT, CH)), but not actually "part" of the grid. For modelling of the physical stuff they don't play a role, right? Maybe we can add them after clarifying the rest.

[amanda-wein]

OEO:transformer: A transformer is an electricity grid component that passively transfers electrical energy from one electrical circuit to another.

On a slightly different topic, this definition is a bit misleading - a transformer often connects two different electrical circuits, but it doesn't necessarily have to. For a distribution-level transformer that steps down from 12kV/4kV/etc. to 240V, the wires and equipment on either side of that transformer would be considered a single circuit by the system operator. I think something like "A transformer is an electricity grid component that passively transfers electrical energy from one voltage level to another" would be a bit more accurate.

[amanda-wein]

And what about "grid level"? That is a new term (regarding this discussion) - it is translated to "Spannungsebene", but that is (should be?) the voltage level. Is there a differnece? What does the geographic coverage (?) has to do with it? An electric system is rarely characterized in terms of any geography (as long as it is not relevant where some part of it is located because someone has to go out to fix something or the like).

As far as I understand "Netzebenen", they are mainly labels for certain types of grids (with a certain voltage level, in a certain region (DE, AT, CH)), but not actually "part" of the grid. For modelling of the physical stuff they don't play a role, right? Maybe we can add them after clarifying the rest.

I would agree that I don't think geographic coverage has much to do with the definitions of grid levels (Netzebenen). The distinction between transmission and distribution grid levels impacts the responsible parties for maintaining and operating the system (TSO & ISO & RTO for transmission, DSO for distribution), the regulatory environment for the system, and the financial market structure for the system. I suppose geography becomes relevant when you're talking about transmission interconnections between different companies/states/countries, since that impacts regulatory oversight and electricity markets.

But from a standpoint of just the physical stuff that makes up the grid (transformers, cables, switches, etc), the names transmission and distribution don't really matter - the operating voltage level (Spannungsebene) is more relevant than the grid level (Netzebene) its assigned to.

[UStucky]

OEO:transformer: A transformer is an electricity grid component that passively transfers electrical energy from one electrical circuit to another.

On a slightly different topic, this definition is a bit misleading - a transformer often connects two different electrical circuits, but it doesn't necessarily have to. For a distribution-level transformer that steps down from 12kV/4kV/etc. to 240V, the wires and equipment on either side of that transformer would be considered a single circuit by the system operator. I think something like "A transformer is an electricity grid component that passively transfers electrical energy from one voltage level to another" would be a bit more accurate.

Regarding transformers:

1. The definition from CIM:
   "An electrical device consisting of two or more coupled windings, with or without a magnetic core, for introducing mutual coupling between electric circuits. Transformers can be used to control voltage and phase shift (active power flow).
   A power transformer may be composed of separate transformer tanks that need not be identical.
   A power transformer can be modeled with or without tanks and is intended for use in both balanced and unbalanced representations. A power transformer typically has two terminals, but may have one (grounding), three or more terminals.
   ..."
2. A UML diagram from CIM showing the model "around" PowerTransformer:
   

And we canot state that a transformer transfers energy from one "voltage level" to another, since these are not (!) voltages, they are related to ranges of voltage values.