Displacement Power Factor (DPF) is the power factor as we know at fundamental system frequency (50Hz in UK). However, True Power Factor (PF) or just Power Factor is the product of the distortion power factor and DPF. Check out the Wikipedia article on this topic. The following equation related components:
Where, 
![\left [\sqrt{1+I_{THD}^2} \right ]^{-1}](http://s0.wp.com/latex.php?latex=%5Cleft+%5B%5Csqrt%7B1%2BI_%7BTHD%7D%5E2%7D+%5Cright+%5D%5E%7B-1%7D&bg=ffffff&fg=333333&s=0 "\left [\sqrt{1+I_{THD}^2} \right ]^{-1}")
The above equation leads to the following conclusions:
- PF≤DPF, True Power Factor is always less than or equal to Displacement Power Factor.
- PF = DPF, True Power Factor equals Displacement Power Factor when there are current harmonics at the point of measurement;
- PF<DPF, suggests presence of harmonics, take it easy: awareness is good.
- PF<<DPF, means its time to take action.
The above observations, comparing DPF and PF will give you a quick assessment of harmonic severity, however if detail assessment is required then you will need to monitor both 
As I understand, most meters or monitoring equipment that display PF and DFC also may have the ability to calculate both current and voltage total harmonic distortion factors:
In UK, DNOs are required to comply with EN50160 Std. and consumers with G5/4-1 Std.
Posted by scvegunta 
value in discharge time 
seconds. Typical discharge resistor ratings for a given power factor capacitor 
in μF or MVAR include: maximum normal operation system voltage 
in kV and required retained discharge voltage 
in kΩ is given as,
(1)
and capacitor step’s rated reactive power output 
in MVAR, the capacitor step’s capacitance 
. Rearrange this for Discharge Resistor ‘R’ and you get (1). Simple!
.
Henry
is the PFC detune frequency and C is the PFC capacitance per phase leg.
