GridSense Line IQ LIQ60, User Manual, Page: 20 / 39

File: LIQ User Manual V2.0
Page 18 of 37
2.4.5 Power Factor Calculation
Overview
This overview gives a brief introduction to Power Factor values, i.e. what is meant by Displacement
Power Factor and True Power Factor.
See Appendix A
–
LineMan which explains how to use LineMan to configure an LIQ-60 to measure
Displacement Power Factor.
What Information is provided
The LIQ-60 records the phase angle between the fundamental (50/60Hz) voltage and current waveforms,
from which the Displacement Power Factor (DPF) can be derived. This information is made available in
the following formats:
•
Instantaneous DPF and phase angle (including lead/lag) of the line is returned when the LIQ-60
status is queried. These parameters are averaged over approximately 1 minute and updated every
minute.
•
Average DPF and phase angle (including lead/lag) are logged for each load log interval. This
interval can be set to be between 2 and 60 minutes.
Meaning of Power Factor Values
The LIQ-60 will record power factor on power systems operating in all four quadrants of power f l o w .
Positive DPF indicates net energy flow is from source to load and negative DPF indicates net e n e r g y
flow is from load back to the source.
Positive phase angles indicate current is leading voltage (capacitive load) and negative phase angles
indicate current is lagging voltage (inductive load).
Displacement vs. True Power Factor
Displacement Power Factor (DPF) is defined as cos
φ
where
φ
is the phase angle between fundamental
(50/60Hz) voltage and current waveforms, whereas True Power Factor (TPF) is defined as the ratio of
Real Power (in watts) to Apparent Power (in VA). In the case of sinusoidal waveforms, DPF = TPF,
however they are no longer equal for non-sinusoidal waves such as those containing harmonics.
The LIQ-60 measures DPF, thus consider harmonic content before inferring the TPF from LIQ-60 readings.
With normal levels of harmonic content on typical power lines the difference between DPF and TPF is
small and usually will be negligible, however if you suspect high harmonic content, a harmonic study
should be performed if knowledge of TPF is critical.
Defining Load and Source Directions
To determine how to correctly record power factor the LIQ-60 needs to know which way it is mounted
on the power line, i.e. which direction is towards the source and which is towards the load. Under most
conditions with a single generation source this will be easy to define. In the case of power lines with
multiple
generation sources you must choose which direction to call the ‘source’ and which the ‘load’.
LineMan provides an interface to set the load direction of the LIQ-60, as determined by the direction of
the reference arrow on the bottom of the LIQ-60.