HT instruments PQA820 - Manual (Page 28)

PQA820
EN – 27
NOTES
 Please note that, strictly speaking, the expression of phase reactive power in a non-
sinusoidal condition would be incorrect. As to why, it may be useful to think that both
the presence of harmonics and the presence of reactive power produce, among other
effects, an increase in in-line power losses due to a higher efficient value of current
 With the above-indicated relationship, the increase rate in power losses due to the
harmonics is algebraically summed to that introduced by the presence of reactive
power. In fact, although the two phenomena contribute to causing an increase in in-line
losses, it is not generally true that these power loss causes are in phase with each
other and therefore algebraically summed
 The relationship above is justified by its relative simple calculation and by the relative
difference between the value obtained with this relationship and the real value
 Also note that, in case of an electrical system with harmonics, a further parameter
called depurated power factor (dPF) is determined. In fact, this parameter represents
the theoretical limit value the power factor can reach if all harmonics are completely
eliminated from the electrical system.
12.3.1. Conventions on powers and power factors
As regards recognizing the type of reactive power, the type of power factor and the sense
of the active power, the conventions reported in the following scheme are adopted, where
the angles indicated are the currents phase angles to voltage (e.g. in the first quadrant the
current is 0° to 90° delayed compared to voltage):
Q
Capacitive generator Inductive load
90°
II Quadrant
180°
P+ = 0
Pfc+ = -1
Pfi+ = -1
Qc+ =
0
Qi+ = 0
P - = P
Pfc - = Pf
Pfi - = +1
Qc- = Q
Qi - = 0
P+ = P
Pfc+= +1
Pfi+ = Pf
Qc+ =
0
Qi+ = Q
P- = 0
Pfc- = -1
Pfi- = -1
Qc- = 0
Qi- = 0
I Quadrant
0°
P
III Quadrant
P+ = 0
Pfc+ = -1
Pfi+ = -1
Qc+ =
0
Qi+ = 0
P - = P
Pfc - = +1
Pfi - = Pf
Qc- = 0
Qi - = -Q
P+ = P
Pfc+= Pf
Pfi+ = +1
Qc+ =
Q
Qi+ = 0
P- = 0
Pfc- = -1
Pfi- = -1
Qc- = 0
Qi- = 0
IV Quadrant
270°
Inductive generator Capacitive load
The meaning of the symbols used and of the values they take in the above-reported
scheme is described in the following tables: