Meter Data - Active power looks normal before going negative on two phases

[swil]

Hi,

What could be happening for active power data in the lower half of the screen shot that follows? The upper half of data shown seems to suggest CTs aren't wired backwards (powers balanced and positive, power factor plausible).

From 8:47 am what could be happening?

[Yut]

Where is the 08.47AM data ?

[swil]

Good Point Yut.  

Turns out there was a major phase shift when loads turned on, meaning that the current phase order changed.

Not sure what was causing it.

[Charles_Murison · Accepted solution]

Hello Swil,

2 items to consider: for a CT, at low currents, the accuracy of the CT is in question, usually a rule of thumb is 10% primary rating is required for the CT to be saturated and accurate. Different CTs have different starting points. Second point, each meter has a minimum amount of current for the meter to be accurate This is usually found in the technical datasheet for the meter.

It is very possible at the low current levels the Phasors look correct, however once load is applied it can be determined that the wiring/configuration is not correct. I suspect something that that is happening now.

[DanL · Accepted solution]

swil, I believe your attached screenshot shows:

1. Load off (zero power on all phases) from 07:26 - 07:31
2. Load on (Quadrant 1, 90% Ind) from 07:32 - 07:43 (end of data provided)

It does not show data for 08:47 nor any "phase shift".

Regardless, a system/wiring diagram would likely be required to provide context for the data.