Add descriptors for components of the Ohm law and differentiate AC and DC current

[areleu]

Description of the issue

In existing classes like HVDC-line and AC-line we refer to the term current. This is also necessary to describe the differences of AC and DC charging processes that may come out of #1444

Along the same lines we have things like resistance and voltage

Ideas of solution

This should not be very complicated to implement since we already have some parallels. Using for example the water flow axioms.

water flow has process attribute some water flow rate
water flow rate has quantity value some volumetric flow rate value

We could add the axioms for electrical energy transfer:

electrical energy transfer alternative label current or electric current
electrical energy transfer has process attribute some current intensity
current intensity has quantity value some current intensity value

electrical energy transfer has process attribute some resistance
resistance has quantity value some resistance value

electrical energy transfer has process attribute some voltage
voltage has quantity value some voltage value

Definitions:

current intensity: "Current intensity is the process attribute of an electrical energy transfer which quantifies the rate of electrons flowing through it."

resistance: "Resistance is the process attribute of an electrical energy transfer which quantifies the opposition to electron flow."

voltage: "Voltage is the process attribute of an electrical energy transfer which quantifies the electron flow potential differences of its starting and ending points."

We could also add subclasses of electrical energy transfer:

Alternate current: "An alternate current is an electrical energy transfer whose charge changes during the flow"

Direct current: "A direct current is an electrical energy transfer whose charge is constant during the flow"

I was also thinking of axiomizing charge but, since alternate current changes the charge constantly this may be tricky. What we could have is still define charge as an attribute but not axiomize it.

Please let me know if you agree with these definitions, I would like to implement them asap as I need them for work.

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

[l-emele]

Some thoughts on these proposals:

• I don't think, an electrical energy transfer is the same as an (electrical) current. A current value is a value that measures how much charges per timestep are transfered; it does not measure how much energy. I rather suggest something like: An electrical current is a process of moving electric charges. (Adapted from the definition of water flow: Water flow is a process of liquid water moving.)
• The label current intensity is confusing, as in physics intensities are often referred to as per area quantities, in this case something with the unit A/mm². See also Merriam-Webster.
• A resistance is a property of an object (e.g. a resistor), not a process attribute of an electrical energy transfer or a current. The object has this property independently of whether an electrical current flows momentarily through it or not.
• AC versus DC: Not the charges themselve change but the direction of flow of charges changes periodically in AC. But the energy flow also in AC always in one direction. Therefore we should define AC and DC as subclasses of current and not of electrical energy transfer.
  • direct current: A direct current is an electrical current in which electrical charges flow always in the same direction.
  • alternative current: An alternative current is an electrical current in which electrical charges periodically change their direction of flow.

[areleu]

Some thoughts on these proposals:

* I don't think, an electrical energy transfer is the same as an (electrical) current. A current value is a value that measures how much charges per timestep are transfered; it does not measure how much energy. I rather suggest something like: _An electrical current is a process of moving electric charges._ (Adapted from the definition of `water flow`: _Water flow is a process of liquid water moving._)

* The label `current intensity` is confusing, as in physics intensities are often referred to as per area quantities, in this case something with the unit A/mm². See also [Merriam-Webster](https://www.merriam-webster.com/dictionary/current%20intensity).

* A `resistance` is a property of an object (e.g. a resistor), not a process attribute of an electrical energy transfer or a current. The object has this property independently of whether an electrical current flows momentarily through it or not.

* AC versus DC: Not the charges themselve change but the _direction of flow_ of charges changes periodically in AC. But the energy flow also in AC always in one direction. Therefore we should define AC and DC as subclasses of current and not of electrical energy transfer.
  
  * `direct current`: _A direct current is an electrical current in which electrical charges flow always in the same direction._
  * `alternative current`: _An alternative current is an electrical current in which electrical charges periodically change their direction of flow._

I agree with all of this, but we are still missing the alternative to current intensity, the term to represent the quantity value of electrical current as a process, so, the value with units A.

We could also create the two terms and give them the same label, it is how they are used in the literature and the unique IDs prevent conflicts. Other alterantive is to have them labeled like:

electrical current (process)
electrical current (value)

[areleu]

By the way, I was suggesting resistance as property of the process because although, each object indivitually has its resistance. When multiple resistances in series or parallel are taken into account in a circuit, we talk about total resistance.

[l-emele]

I browsed a bit Wikipedia and found

• that intensitiy has various meanings in physics and
• that there is a distinction between current intensity and current density with the first being a synonym to current (the process) and the latter the entity that is measured in A/mm².

So what about using

• electrical current or current as label for the process,
• electrical current intensity or current intensity as label for the process attribute,
• electrical current intensity value or current intensity value or electrical current value or current value for the quantity value?

If have to define later something for A/mm², then we can still use electrical current density, but I think that is not necessarily at the moment.

By the way, I was suggesting resistance as property of the process because although, each object indivitually has its resistance. When multiple resistances in series or parallel are taken into account in a circuit, we talk about total resistance.

Yes, true. But this total resistance of the circuit is still a property of the circuit (made up of individual objects) and still not a property of the of the current.

voltage: "Voltage is the process attribute of an electrical energy transfer which quantifies the electron flow potential differences of its starting and ending points."

I don't think that this is a process attribute of a electrical energy transfer either, as there can be a voltage without transferring energy. At the terminals of a battery there is a voltage, even in moments when no energy is transfered from or to the battery.
EDIT: The voltage unit volt is defined as work per charge unit. This should give a hint how to define voltage.

[stap-m]

Did someone check, whether there exist already ontologies that contains these concepts in a manner that we could import / adapt?

[l-emele]

I looked into PATO and ENVO, but did not find anything helpful. The only helpful things in other ontologies are the mentioned definitions of the associated units in the units ontology.

[areleu]

I have been looking for use cases, and one thing that I have often noticed is that the current intensity is not that much used to describe Transmission line infrastructure, it is mostly voltages and power capacities. Examples: Wikipedia, IEEE RELIABILITY TEST SYSTEM

Not that we keep the terms out, I think they are still valuable but probably we can afford more complexity in the other terms and keep current simple.