Difference in harmonics between phases

[jerry_IPACS]

Hi everyone, 

I have been getting a strange issue from some of the ION 9000 meters that we have installed on a site recently. Some of the meters seem to have different THD measurements on phase A compared to phases B and C. For example, the THD mean measurement on phases B and C are rougly 10-15% whereas the same measurement on phase A is around 1% (refer to attached images). Its strange because the THD high measurement on all three phases is somewhat consistent, but just the THD mean measurement on phase A is off). Has anyone come across this? I was thinking that it is due to some meter firmware issue, but I have the latest versions of the firmware installed on all the meters. Any guidance would be much appreciated. 

Regards, 

[DanL · Accepted solution]

Double check your software (report?) configuration.

The first attachment "Phase A.png" appears to plot the HIGH (red) current THD and MEAN (green) current THD on phase A. These do not appear to be voltage THD plots.

The second attachment "Phase B.png" does not have a legend, but presumably it is HIGH (red) current THD and MEAN (green) current THD on phase B.

There does not appear to be any phase C data nor voltage THD data.

Without knowing anything about the system being monitored, the provided plots do not look exceedingly strange to me.

Double check your meter is configured to log THD the way you want. THD can be configured to be %fundamental, % RMS, % Nominal, and/or % Demand.

When using %fundmantal and/or %RMS modes, high THD ratios are common when the load is very low. You may need to correlate the data with load levels to interpret the THD (or use an alternate THD mode to mitigate this effect)

Lastly, you should perform a "manual waveform capture" trigger and view the waveform capture