Power Meter several parameters: active power, reactive power, active power, reactive power, power factor, and so is directional, the normal positive, the opposite direction is displayed as negative, but some instrument will do some processing, such as the power factor is negative, the process value, coupled with capacitive (-II-) symbol ", looks for the positive.
2, when the active display to a negative value, and certainly for the following reasons: anti-Transformer FEEDTHROUGH current direction and (P2, P1 out), or reverse the polarity of the transformer (S1 and S2 reverse);
3, when the reactive power is displayed as a negative value, while the active display is positive, it can be sure the load is capacitive load;
4, power metering is generally very little is negative, if the current transformer opposite direction, or wiring errors generally eventually lead to the inaccurate measurement or measurement, will not be negative. If value is most likely as a capacitive load.
5, if only the power is negative, while the N line current is 0, then either display a negative phase voltage line connected to each other wrong.