Understanding Results from Meter

[LoadMonitor]

Hi can anyone tell me if I had the following readings how could I calculate kw. The readings were taken from an electricity meter which logged the values every 15 minutes and the values below are what were recorded in the first 15 minute period;

A+ Energy Total = 3920Wh
A- Energy Total = 3480Wh

Q+ Energy Total = 3960varh
Q- Energy Total = 2920varh

S+ Energy Total = 3920Wh
S- Energy Total = 7440Wh

Really what I need to figure out is how do you get the absolute values based on the positive and negative values.
I think as the values have h after them they are hour values, but as the values are recorded every 15 minutes I am not sure what to do with them.
Also I believe the values A,Q and S make up the power triangle but I cant get the equation to balance if you square them.
I have tried adding them and squaring them but I still cant get it to balance.
Any help appreciated.

 

[DRWeig]

Can you look at the manual for the meter and tell us what A+, A-, Q+, Q-, S+, and S- are supposed to mean?

Maybe tell us what make and model of meter you're looking at?

Those terms are not familiar at all to me...

Perhaps someone else will recognize them, though.

Good on ya,

Goober Dave

 

[stevenal]

15 minutes is a 1/4 hour, so the 15 minute energy in Wh would be divided by .25 h to get average power for the period in W. Divide by 1000 to get average kW for the period.

The symbols make no sense with the units given.

 

[LoadMonitor]

The meter is an Iskra MT375 3 phase 4 wire meter.

I have attached the brochure for the meter. The manual is not much use however based on the software it says as follows;

A+ All phase energy total Import
A- All phase energy total Export
Q+ All phase energy total Import
Q- All phase energy total Export
S+ All phase energy total Import
S- All phase energy total Export

Apart from that the only clue I have is the units of measurement which show as follows;

A = Wh
Q = varh
S = Wh

My problem is I cant get these figures to balance if they are the three elements of the power triangle. Also if it has recorded import and export values I am confused. The recordings were taken from a school so I am not sure how the export values have come about and how would that fit in with there overall kw usage.

The meter also recorded voltage and current so I have been able to calculate kw but I will need to explain what the different elements are.

 

[stevenal]

Perhaps A stands for active energy. This matches the units given.

Q usually stands for reactive power, but here the units given are for reactive energy.

S usually stands for apparent power, but the units are all wrong. Apparent power units are VA, and apparent energy units are VAh.

Seems odd you would see import and export (+ and -) during the same 15 minute interval. Do you have sources on both sides of the meter? Possibly you have a CT reversed so you are measuring import and export values simultaneously?

 

[jghrist]

You are reading energy from the time that the meters were reset or initially installed. To determine the average W, var, and VA for some period, you have to record at the beginning and end of the period, subtract ending kWh & kvarh, then divide by the time period in hours.

 

[LoadMonitor]

Hi

The figures I have quoted are what you are left with after you take the reading at the start of the first 15 minute period away from the reading at the end of the first 15 minute period. If you divide these by the time period in hours (i.e. 0.25)then they still don't balance.

 

[potteryshard]

Electronic meters come with default programming, but most utilities pick and choose what setting parameters they individually want, and then re-program the meters to match that internal convention. You will probably have to talk to the owning utility to determine what the as-installed nomenclature and units measured actually are. The 'A' reading for example could be anything from actual to Alice's department. Displays are infinitly customizeable.

 

[jghrist]

What is the installation? It doesn't make sense that during one 15 minute period, there was 3,920 Wh imported (load) and 3,480 Wh exported (generated) through the same meter.

 

[LoadMonitor]

The installation is in a school. The meter is int owned by the utility company and is not the meter been used for billing purposes. It was only supposed to be used to highlight any problems such as excessive loads during night time.

The problem is I cant make any sense of the reading. I cant see how the school would even have exported load.

 

[stevenal]

With no on-site generation, there will be no active energy exported. Explain this to the utility metering department, and suggest their meter is faulty or miswired.

Nothing in the data sheet suggests that miswiring can be identified and alerted (except for phase voltage presence), or that per phase values can be obtained or even power factor. Any of these features would be helpful. All is dependent on the skill of the installer to ensure polarities are correct and the phases match.

 

[FreddyNurk]

I don't recall the details, but I remember asking about a similar situation a few years ago whereby the meter was reading import and export values but there was no onsite generation either. I never got to the bottom of the issue (the company went into receivership two weeks after I was asked to look at it) but someone here mentioned about setting up metering in such a manner as to avoid issues with meter tampering or similar.

The obvious one is CT miswiring or similar, but I'm sure that there was another explanation for it. Waross may have been the respondent at the time, but it may well have been others too.

 

[stevenal]

thread238-224067

 

[waross]

Check the connections carefully. Do you have a link to an instruction manual for the meter?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

No, do not check the connections. This requires a qualified individual, and the meter does not belong to the OP.

 

[waross]

In this post,

The installation is in a school. The meter is int owned by the utility company and is not the meter been used for billing purposes. It was only supposed to be used to highlight any problems such as excessive loads during night time.

I assumed that
"meter is int owned by the utility company"
was a typo and should have read "the meter is not owned by the utility."
I may have been mistaken.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LoadMonitor]

The meter manufacturers have told me;

A+ All phase energy total Import is Imported kWh total consumption (active power)
A- All phase energy total Export is Exported (generated) kWh total (active power)
Q+ All phase energy total Import is Imported kVArh total (reactive power)
Q- All phase energy total Export is Exported kVArh total (reactive power)
S+ All phase energy total Import is Imported kVAh total (apparent power)
S- All phase energy total Export is Exported kVAh total (apparent power)

Given this info the only explanation I can see for the exported figures is the CT's were installed the wrong direction. However if you also take these as been imported figures the figures still don't seem to add up.

 

[racobb]

First off, we haven't seen any updated values lately. Are your exported values still changing every 15 minutes. Could be that it was originally connected wrong and these values are still in memory. If they are still updating then that is not the case and maybe the meter is still wired wrong. Your numbers do seem to indicate that. The kVA does not even closely match what it should be reading.

In any case there are still some basic verification tips available to you....as in Root3 X volts X amps(average per phase) = Total Power in VA. Have someone check the volts and amps and then do the math to decide what the load actually is, being sure to account for any metering transformer ratios. You say it is a school, then start with about a 90% power factor and calculate the instantaneous kW from there. You probably will be close enough at least to verify that the meter is either right or wrong. To do that take the nearest 15 minute value of A+ and multiply by 4 and see how close you get.

With all due respect, I have to say that it is fairly simple and if you do not understand the concepts, you should engage someone who does.....Good Luck

Alan

 

[stevenal]

The manufacturer is wrong, since all the units ending in "h" are types of energy, not power.