Troubleshooting: the so-called accuracy problem
Troubleshooting: the so-called accuracy problem
Welcome to discuss the issue about this blog here https://imeter.club/topic/232
Both the WEM3080 series(single phase energy meter wifi) and WEM3080T series(three phase energy meter wifi) are the accuracy of class 1 ,all meters are calibrated independently before leaving the factory, so accuracy is promised.
If you have just installed the energy meter and doubt about the reading, this article would help you to solve the problem regards to the accuracy.
There is an export energy reading
You have not installed the solar pv inverter in your system but there is a export energy (means there is an energy exported to the grid) reading, such as the pics below.
CT has been installed in a wrong direction
This is the most common cases that cause a wrong reading.
The energy meters (both single phase and three phase) are all bi-directional measurement. Even your system do not have exported energy, the CT installation direction (K->L) should also be the same with the manual ,such as below.
Please note ,the below pics is just one situation, how to install the CT in a correct direction ,please refer to
If the CT is installed in the wrong direction, it would cause the imported energy reading would be counted into the exported energy, and the positive power reading would also displayed as a negative power reading.
In normal mode(not net energy metering mode), both imported and exported energy reading are the sum of three phase. So if one phase that CT installed in the wrong direction, there will be the exported energy reading displayed in the graph.
Please note: If your system include solar PV inverter, you still need to pay attention to the CT direction. As described above ,the wrong CT direction in one phase will make the imported and exported energy counted wrong, and because there is indeed a solar PV output in your system ,this mistake will be more difficult to be found out.
Phase mismatch in installation
For example, you connect the voltage of Ua,Ub and Uc in the phase A,B and C But you clamp the CTa in the wire of phase B(or some similar case) , the power and energy of phase A will be calculated totally wrong in this case, and the sum of the power and energy will totally wrong either.
The power reading of each phase is the active power. Active power = U*I *Power factor Power factor = cos(angle between U and I) If you clamp the CTa on the wire of phase B, when it calculate the active power of phase A, there will be a extra 120 degrees phase angle difference (between phase A and phase B) , this will caused the active power and energy reading calculation totally wrong .
The amp reading of the energy meter is different from the multimeter
The amp reading difference between the energy meter and the multimeter is because the amp reading of our energy meter is the "true RMS" value, while the multimeter reading is the RMS value. The two values will be a dramatic difference if the circuit load is complicated (we have met a 30% difference before)
This is a introduction to the difference between true RMS and RMS
https://www.tester.co.uk/blog/electrical/multimeter-jargon-busters-true-rms/
if you want to compare the amp reading, please select a multimeter that can measure the "true RMS" value of the amp.
Or you can check whether your two multimeters in hand can measure the "true RMS" value of the current.
How to confirm whether the energy meter is damaged during shipment.
This possibility is very low.
You can compare the consistency of three phase to check whether the meter is damaged during the shipment.
Connect Ua Ub and Uc together to the voltage of phase A, clamp CTa Ctb and Ctc also to the wire of phase A. Then compare the power ,voltage, current the the there phase reading, if they are nearly the same, it means the consistency is OK, then it will also prove the device is not damaged during the shipment.
Find your installation problem quickly
when such a phenomenon appears, it means you installed ct in the wrong direction or phase mismatch.
There is negative power reading in the meter type of "grid", but there is no solar PV inverter in the system
Negative power reading means there is exporting energy to the grid. It should not happen in the system that without solar pv inverter.
You can find the negative power reading in this page.
Or this page
There is a negative power reading during the night time in the meter type of "grid"
Negative power reading means there is exporting energy to the grid. It should not happen during nighttime.
There is a negative power reading in the meter type of inverter
The power reading should always be positive in the meter type of "inverter".If there is negative power reading appears, it means a wrong installation.
