Meter settings incorrect, is there an equation to determine proper values?

[Douglas.T]

Hi Everyone,

First time poster. I have a submeter (Allan Bradley Power Monitor) that has been collecting data. Unfortunately, the settings of the submeter were incorrect, leading to inaccurate values. I would like to correct the historical data. How do I determine the scaling factor to apply to the historical data?

Here are the changed settings:

	Actual Settings	Correct Settings
Circuit setting	Open Delta	Wye
CT Ratio	1200:5	400:5

I am pretty comfortable finding a scaling factor based on the change in CT ratio, but how do I take the circuit change into account?

 

[junkhound]

sqrt (3)

 

[electrofelon]

sqrt (3)

That is not clear to me. Why would there be a 1.732 factor?

 

[topgone]

Hi Everyone,

First time poster. I have a submeter (Allan Bradley Power Monitor) that has been collecting data. Unfortunately, the settings of the submeter were incorrect, leading to inaccurate values. I would like to correct the historical data. How do I determine the scaling factor to apply to the historical data?

Here are the changed settings:

	Actual Settings	Correct Settings
Circuit setting	Open Delta	Wye
CT Ratio	1200:5	400:5

I am pretty comfortable finding a scaling factor based on the change in CT ratio, but how do I take the circuit change into account?

First, RTFM!
May we know what model of power monitoring unit you got there?

 

[Ingenieur]

If v is correct then adjust P and i x 1/3

 

[gar]

161125-1730 EST

junkhound:

Explain why.


Douglas. T:

You need to provide more details on your instrument connection. A 3 phase 3 wire system requires 2 wattmeters, a 3 phase 4 wire system requires 3 wattmeters.

If you were measuring a 4 wire wye, then 3 current and 3 voltage inputs are required. If the instrument as programmed did not assume the wye configuration, then if there was an unbalanced current in the neutral you probably have some power error that is not correctable (therefore energy). But this may be small, depends upon the amount of unbalance.

Certainly you need to correct for the current transformer ratio error, which is simply the ratio. No idea how the instrument handled voltage calibration. In delta line to line voltage would have been measured. If the correct line to line voltage was programmed in, then my guess is that no voltage correction would need to be done.

To get an estimate for a correction factor set the system up as it was incorrectly programmed. Measure a relatively known load for a while, and obtain a value. Then program correctly and rerun the experiment. Take the ratio. Does this compare in any way with what I described above?

.

 

[Douglas.T]

161125-1730 EST

junkhound:

Explain why.


Douglas. T:

You need to provide more details on your instrument connection. A 3 phase 3 wire system requires 2 wattmeters, a 3 phase 4 wire system requires 3 wattmeters.

If you were measuring a 4 wire wye, then 3 current and 3 voltage inputs are required. If the instrument as programmed did not assume the wye configuration, then if there was an unbalanced current in the neutral you probably have some power error that is not correctable (therefore energy). But this may be small, depends upon the amount of unbalance.

Certainly you need to correct for the current transformer ratio error, which is simply the ratio. No idea how the instrument handled voltage calibration. In delta line to line voltage would have been measured. If the correct line to line voltage was programmed in, then my guess is that no voltage correction would need to be done.

To get an estimate for a correction factor set the system up as it was incorrectly programmed. Measure a relatively known load for a while, and obtain a value. Then program correctly and rerun the experiment. Take the ratio. Does this compare in any way with what I described above?

.

Thanks everyone for the input and explanations. It is an Allen Bradley Power Monitor 1000 1408-TR2A-485 but unfortunately do not currently have access to any wiring documentation. I am going to advise my client that we would need to run an experiment to determine the scaling factor.

Cheers!

 

[ATSman]

Depending on the AHJ or entity you are presenting this power survey to, to re-scale the recorded
values may not be acceptable (especially like in hospitals out here where the EEOR can be a real PITA.)
I would hook up the meter with the proper settings, perform a second survey and chalk up
the lost time to experience.