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Guru
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Join Date: Mar 2010
Location: In the pool because it is too hot.
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EKM Metering, What is Happening?

04/03/2012 4:14 PM

Dear Fellows,

I post some pictures of my metering system for solar Grid tie:

The meter has an interface and also measures:

1. Used power in kWh

2. Power sent back into the grid

3. Line voltage between L1 and L2

4. Measured current

5. Real time power involved

6. Power factor of L1 and Neutral

7. Power factor of L2 and Neutral

The display show these items with an interval of a few seconds.

They call this power (usage) meter 3- wire although I only had to feed the 2 phases through it. The metering works with 2 CT's mounted inside.

Installed are 2500 Watts panels and here are the readings:

Here it shows the line voltage.

And below the amperage:

10.8 Amperes on the display. When I measure L1 and L2 separately with a clamp meter (True RMS), I read about 5.2 and 5.4 - a small discrepancy but when I measure the current through the neutral, I find the difference of 0.2 ampere.

A strange situation occurs when I check the Power (in kW) real time.

The display gives me not what I expect.

Has anyone experienced this before and what is you explanation behind it?

Thanks for your input. D.

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Guru
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Location: Alabama
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#1

Re: EKM metering, what is happening?

04/03/2012 4:34 PM

Quote"A strange situation occurs when I check the Power (in kW) real time.

The display gives me not what I expect. "

The meter is reading KWH's not kw. Some meters will allow you to push a button and read the kw at that instant. I may not understand your question correctly. If not maybe you can clear it up.

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Guru
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Join Date: Mar 2010
Location: In the pool because it is too hot.
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#2
In reply to #1

Re: EKM metering, what is happening?

04/03/2012 5:31 PM

Hi Wareagle,

The meter is a smart meter and reads (power consumption - position 1 - no picture shown- I might have expressed myself wrongly - in kWh - totalizer)

Power indeed is expressed in Watts. (Voltage X Current)

I do not know how to define the "work" as we put it in Europe, when a time factor is involved (= Power X time)

Position 2 - also not pictured totals the kVAR (or in my case the total of kVAh produced by the solar setup)

When the display shows U that is the line voltage, A is the current, and P is the power in kVA or kW.

The imprints on the smart meter may be confusing, but only counts for positions 1 and 2 - not pictured.

Thanks for the clarification. D.

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Guru
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Join Date: Jun 2008
Location: Alabama
Posts: 1629
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#3

Re: EKM Metering, What is Happening?

04/03/2012 7:36 PM

#1 voltage 246.9

#2 amps = 10.8

#3 power = 1181 kw I think

You are reading about 5 amps per leg so

kw = 5.3(avg) x 246.9 x pf .90 (guess) = 1177 kw which is close to

the meter reading. I don't know if the amp reading of 10.8 is the max reading during

the time period or not.

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Guru
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Join Date: Mar 2010
Location: In the pool because it is too hot.
Posts: 2753
Good Answers: 130
#4
In reply to #3

Re: EKM Metering, What is Happening?

04/03/2012 10:47 PM

I think, according my readings with the clamp, that the current on the display is the total of Leg 1 + Leg 2 + The current, I measure through the neutral.

The figure makes sense that way.

Just find it very strange that the EKM doesn't calculate the shown voltage 246.9 V times the shown current 10.8 A as P- value.

The panels together here produce a lot more than 2500 Watts. Each leg has its own inverter, delivering half the voltage between neutral and leg(s)

The unbalance (current through the neutral) I think is created, because one leg has an extra small inverter (80 Watts) This leg has a pf of 0.99, the other has a pf of 1.

The EKM meter says 3- wire, but there is no reference to the neutral connected. There is only a provision for 2 wires.

Probably it measures only one leg, but how? The EKM has 2 CT's in it. The voltage it reads between the 2 legs. And this brings a faulty reading on the display. Looks like it indicates about only half of the produced Watts? (and probably also the kWh?)

With the sun we have here, the output is pretty stable. The display readings jump to the next item every 3 seconds and the measurement is taken every 1/2 second.

The figures do not change a lot during one sample cycle.

Tks

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