#446 Proposal: Comprehensive Tags for Electrical Meters

Stephen Frank Mon 10 Oct 2016

Short Version

Our Haystack working group on point tags for electricity meters and other electrical equipment has put together a comprehensive proposal for expanding Haystack to better cover the variety of points found in electricity meters. Comment from the Haystack community is invited and welcomed.

The proposed tags and revised documentation are available in the Haystack Bit Bucket repository: https://bitbucket.org/project-haystack/haystackws/commits/all

A zipped version of the Haystack docs that can be launched and viewed locally that includes these changes is available from: https://dl.dropboxusercontent.com/u/2919598/haystack-3.0.2.zip

For those not easily able to host and view the docs, you can see the new tags and docs in the following source code files in the repo:

/src/haystackws/docs/Energy.fandoc (Elec Meter section)
/src/haystackws/equips/elecMeter.txt
/src/haystackws/tags/energy.trio

Please provide feedback as comments on this thread.

Longer Version

This proposal grew out of several earlier, more concise and less formal proposals, a couple of which were Haystack forum threads. At Haystack Connect 2015, we formed an informal working group to address electrical meter tags. Over the past year and a half, our informal working group has put together the proposal presented here.

Covered Tags

The proposal introduces tag revisions and new tags that cover a large majority of the types of electrical quantities that are measured and recorded in buildings or by electrical power quality meters. The following excerpt from the proposed new documentation summarizes the new tags:

The primary measured quantities in an electrical system are:

  • power: typically measured in "kW"
  • energy: typically measured in "kWh"
  • volt: typically measured in "V"
  • current: typically measured in "A"
  • freq: typically measured in "Hz"
  • pf: power factor

AC power measurements are further qualified by:

  • active: typically measured in "kW" (assumed as default)
  • reactive: typically measured in "kVAR"
  • apparent: typically measured in "kVA"

Voltage and current measurements are further qualified by:

  • mag: magnitude (assumed as default)
  • angle: phase angle, typically measured in "deg"
  • imbalance: imbalance between phases, measured in "%"
  • thd: total harmonic distortion, measured in "%"

Three phase electicrical measurements are qualified by:

  • phase: A, B, C, AB, BC, CA, N
  • avg: for current, voltage, and power factor (assumed as default)
  • total: for power and energy (assumed as default)

Energy exchange with the utility is qualified by:

  • import: energy imported from the grid
  • export: energy exported to the grid
  • net: net exchange (assumed as default)

In addition we define the following general purpose tags:

  • ac: alternating current
  • dc: direct current

What Is Not Covered

We do not propose any new equip-level tagging to distinguish different kinds of electrical equipment (e.g. transformers, solar or wind generation, PQM meters, batteries, etc.). This is still something we (and others) would like to tackle, but there has been less discussion on it and we felt it best to move ahead with the general electrical tags first. Anyone interested in helping with equip-level tags should contact me at Stephen.Frank@nrel.gov, or contact Brian Frank at Sky Foundry. (No relation, by the way.)

We also do not propose tags that are specifically relevant to particular kinds of electrical equipment, such as charge and discharge tags for batteries (just as an example). We felt these might be better handled as part of the equip-level tag proposal for introducing new pieces of electrical equipment.

Also, we didn't introduce phase values for single-phase systems (such as L1, L2, LL, or LN), but those could be added if the community feels a strong need for them.

Related Forums Threads

For reference, here are threads with past proposals and discussion:

These are the ones I know about. It may not be a complete list.

Keith Bishoρ Tue 11 Oct 2016

Stephen

You and the rest of the group have done a great job on this proposal.

I have a few comments for your consideration:

  • pf: power factor” doesn’t state “typically measured in pf”. I completely agree that power factor is actually unit-less and that the “pf” unit is something that has existed, somewhat incorrectly, for a long time in this industry. I think we either need to state “typically measured in pf” or remove the “pf” unit type. I’m good with either path. If we don’t make one of these changes, we are going to look inconsistent.
  • How did we arrive at the using an active tag instead of a real tag? (real power vs active power) This isn't something that we need to change, but we probably need to document. These terms are used interchangeably in other documentation and I could see this question coming up in the future. I think we just need to document the reasoning behind the choice.
  • ac vs dc. Should this be combined into a single tag such as elecFlowType or elecCurrentType: “ac” or “dc”?
  • One of the other past proposals mentioned a need for delta vs wye tagging. I could see this being important in verifying (commissioning) that the meter was set up correctly and producing the correct power values. Maybe a threePhaseConfig tag?

Just a few thoughts that we should probably discuss.

Stephen Frank Tue 11 Oct 2016

Keith: thanks for your input. Before I jump in with my personal thoughts, I want to wait a bit longer to see if others have thoughts (on your comments or in general).

Stephen Frank Fri 14 Oct 2016

Update with a comment I received off forum:

Another engineer asked why we had selected active over real, given that both are common but real is more common, in his perception. This is the same question Keith asked.

I don't know that we have a strong preference on this point, and I can't recall originally why we selected it. There are two minor reasons I can think of:

  • real is a very generic term, vs. active being a slightly less generic term. active therefore feels a little more precise and formal.
  • active seems to pair better with reactive, vs. real pairing with imaginary. We chose active / reactive vs. real / imaginary.

Neither of these is particularly strong. I've seen both so many times that I can't say which is more common. A Google search for...

  • "real, reactive, apparent" yields about 7,920,000 results
  • "active, reactive, apparent" yields about 29,200,000 results

Hits referencing both real and active show up in the top 5 on both search results.

If others feel strongly about using real, I think we can change to real. I'd really like some more active input from others before we make a change, though. (Pun fully intended.)

Stephen Frank Thu 27 Oct 2016

For posterity: Keith and I had a conversation about some of the items above. Here is a record of what we discussed:

  • The pf tag description should be modified to reference the pf unit in some way. We'll work on that.
  • There is not a strong feeling on active vs. real. real appears to be slightly more common but is also somewhat less precise, so we will stick with active.
  • On the topic of ac vs. dc, the main concern is that these are mutually exclusive, so does it make sense to construct the tagging to prevent them from being simultaneously applied? In response: all the groupings of tags listed are mutually exclusive sets. (The full documentation makes this clear, but it was not in my summary above.) Elsewhere, Haystack has not typically used name:value constructs to enforce mutually exclusive sets, so, for consistency, it is probably not a good fit here to do this only for ac vs. dc. (Examples in other contexts include singleDuct / dualDuct / tripleDuct and hot vs. chilled.)
  • The delta vs. wye topic is more of a meter (i.e. equip) level discussion.

Also, we are forming a working group on equip-level tags for electrical equipment. If you would like to participate, please contact me at Stephen.Frank@nrel.gov.

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