Active Power units

[Dave Waterworth]

I downloaded Brick 1.3 draft 1, and I think there's an error in the definition of real/active power (specifically the units).

The definition of power from https://www.engineeringtoolbox.com/kva-reactive-d_886.html is (paraphrased)

• active power (P) - real electrical resistance power consumption in circuit. Active power is measured in watts (W) 
• reactive power (Q) - imaginary inductive and capacitive power consumption in circuit. Reactive inductive power is measured in volt-amperes reactive (VAR).
• apparent power (S) - complex power S = P +jQ. Apparent power is measured in volt-amperes (VA)

But Brick 1.3 defines brick:Real_Power (and equivalent brick:Active_Power) with units unit:V-A, but the definition matches that of P above "(Active Power) is, under periodic conditions, the mean value, taken over one period (T), of the instantaneous power (p). In complex notation, (P = Re \\; S), where (S) is (complex power)"

Should the unit not be W not VA? The unit for brick:Apparent_Power is also unit:V-A (which is correct).

I'm also not entirely sure that the description should be average over period. In my experience it's the instantaneous vector quantity?

[Gabe Fierro]

Hi Dave:

We are using the definition of Active Power from QUDT (https://qudt.org/vocab/quantitykind/ActivePower), which uses the V-A units on the quantity and defines the value as being the average over a period T.

I'm CC'ing Steve Ray to see if he can shed any light on this.

thanks!

Best,

Gabe

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[Steve Ray]

I think there might be an error in QUDT on this topic, so maybe you can help me resolve this. 

The quick method is to just go with what you say:

Active (W).  (currently VA)

Reactive (VAR)

Apparent (VA)

...leaving open a question in my mind of the applicable units for "Complex power" which is a skos:broader category in QUDT. Would that be VA, W, or both?

Moving up the skos:broader hierarchy I get "Electrical power". Keep that at just W?

The "applicable units" in QUDT are computed using an algorithm as described here. Basically, the Units point to the QuantityKinds and the reverse links are computed using the algorithm.

Once I have clarity on the correct applicable units at each level of generality, I can adjust the relations to achieve the correct results.

Final note: it is possible that I should refactor our skos:broader hierarchy, but this will take careful consideration.

Regarding the instantaneous vs. (rms) average value, I think that depends on the context.

Steve

[Dave Waterworth]

Hi Steve

Complex power should have units VA in my opinion since it's only applicable to AC power - there's a good explanation here showing the relationships - in particular, complex power is a vector, real/active, imaginary/reactive and apparent power are all scalars (vector magnitudes). I'm not at all familiar with how `broader` works though, but I don't think you can formally assign a broad unit to quantities like electrical power (since AC and DC power are defined differently). Still, informally I believe W makes more sense than anything else.

Dave

[Steve Ray]

Here's what I propose for the QUDT ontology, moving down the skos:broader hierarchy from general to specific:

Power: the many units for power already there, but not the VA family of units. No change.

ElectricPower: "Inherited" from Power. No change

ComplexPower: Just the VA (including prefixed multiples). No change

ActivePower: 

Steve

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[Steve Ray]

Sorry. Hit the wrong button on my keyboard. Will follow with my full response!

Steve

[Steve Ray]

Here's what I propose for the QUDT ontology, moving down the skos:broader hierarchy from general to specific:

Power: the many units for power already there, but not the VA family of units. No change.

 ElectricPower: "Inherited" from Power. No change

  ComplexPower: Just the VA (including prefixed multiples). No change

   ActivePower: Just the W (including prefixed multiples). (Changed from inheriting from ComplexPower)

   ReactivePower: The reactive variants of VA. No change

   ApparentPower: Just the VA, inherited from ComplexPower. No change.

I will be adding a pull request to our repository to make this change. Let me know if you disagree.

Steve

On Thu, Sep 15, 2022 at 5:49 PM Dave Waterworth <wat...@gmail.com> wrote:

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[Matt Steen]

Not sure how useful it is, but here's the def for active power from the IEC, which has a huge online dictionary...

https://www.electropedia.org/iev/iev.nsf/display?openform&ievref=131-11-42