Difference of Power Factor Reading

A difference 0.5° seems like just a tolerance error in measurement to me. You say that the measured input and current magnitudes are the same, I suspect that they really are not. I suspect that the resolution of one or two of the four measurements produces a tolerance window larger than 0.5°.

Red, A power factor of 0.5 translates to an angle of arc cosine (0.5) or 60 degrees, arc cosine (0.1) or 84.25 degrees. Both are lousy power factors but 0.1 is almost all reactive. More than likely OP problem has to do with metering ratio settings on the relay, especially since his actual measurements are consistent.

If the meters are set wrong then how can any of the metrics be considered at all as valid. I tried to interpret the sparse information we do have in a fashion that agrees with itself. If we had the data on the measured current an voltage data along with some phase component then we could identify if these numbers are the dimensionless power power factor values and which or neither are accurate. We still might find that these numbers are the phase angle in degrees or even possibly radians (that would be odd) and that these two meters assume a balance between three phases of currents but the meters are measuring. The difference comes from a single phase current load returning on the neutral.

We have another case of insufficient information to come to any conclusion.

Are there harmonics in load & are both meters reading true pf?.

You should be busy reading the manuals or any other references for the PF metering devices that only you can identify.

Can you borrow a third unit to see if you get any correlation?

If you're really lucky you'll get a third value to really mess with your brain.

Start Googling and learning.

Neither may be correct. An accurate P.F.measurement requires a Schering Bridge or a modified shielded Schering Bridge.

Schering bridge? That's used for measuring capacitance, usually in RF circuits. Although you might be able to use it to the power factor of cable insulation, it's unlikely that you would use it to measure the power factor of an industrial facility.

This complex number measurement can be made using the average of the complex FFT. You have to trigger each measurement in order to average the single channel FFT. Use at leaset 100 averages.

The result will be the real and imaginary components of EACH harmonic. The ratio of each I over R is the PF for each harmonic (check that; I may have it upside down).

If there are several strong harmonics, they can be vectorially summed using standard complex number addition.

Although the input readings are of same magnitude, you have to check the sequence and phase between voltage and current inputs. For example, with PF 1 the angle between Urs and It are 90º...

SMCTR, you are the only one with a plausible answer except that the phase between the line to neutral voltage and the line current is 0 at PF=1.

OP, make sure that the phase A , B, C PTs are connected at the right location on the meter. Same check for the CTs.

Another possibility is the configuration of delta or wye of the PTs or CTs and the power meters. They may be both wrong.

Good luck