4.9 Direction of power and current
4 Measurement functions
Technical description
144
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Active, reactive and apparent power are calculated as follows:
S
P
Q
P
S
Q
Q
P
P
L
L
cos
3
3
2
2
1
1
4.9.
Direction of power and current
Figure 4.9-1 shows the concept of three phase current direction
and sign of cos
and power factor PF. Figure 4.9-2 shows the
same concepts, but on a PQ-power plane.
I
V
R
EF
+
ind
F
or
w
ard inductive po
w
er
current is lagging
cos
=
+
PF
=
+
+
ca
p
F
or
w
ard capacitive po
w
er
current is leading
cos =
+
PF
=
ind
Reverse inductive po
w
er
current is leading
cos =
PF
=
+
ca
p
Reverse capacitive po
w
er
current is lagging
cos =
PF
=
0
°
+9
0
°
UI_Q
uadrants
Figure 4.9-1 Quadrants of voltage/current phasor plane
S
P
Q
+
ind
F
or
w
ard inductive po
w
er
current is lagging
cos
=
+
PF
=
+
+
ca
p
F
or
w
ard capacitive po
w
er
current is leading
cos =
+
PF
=
ind
Reverse inductive po
w
er
current is leading
cos =
PF
=
+
ca
p
Reverse capacitive po
w
er
current is lagging
cos =
PF
=
0
°
+9
0
°
PQ_Q
uadrants
Figure 4.9-2 Quadrants of power plane