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3
3.3 Connection Modes
Equation 13:
=
⋅
S
3
U
32
For S
, the RMS values of the fundamental component are used; as symmetrical load is sup-
1
posed S
= S.
DIN
3.3.5
Three-wire Three-phase Current with Any Load
For this connection mode, the phase-to-ground voltages are not available. Active and reactive
powers are calculated from the formulas of the two-wattmeter (Aron) circuit:
Equation 14:
64
1
∑
=
P
u
64
ν
=
1
This is also valid for the calculation via Fourier analysis. For the reactive power according to clas-
sic measuring devices (electro dynamic power meter), the following equation is valid:
Equation 15:
64
1
∑
=
Q
u
64
ν
=
1
Distortions will cause an additional fault. For the apparent power (classical method), the following
equation is valid::
Equation 16:
(
=
S
3
U
12
For the apparent power according to DIN calculated from the phase voltages, the following equa-
tion is valid:
Equation 17:
(
1
=
2
S
U
12
3
In both cases, current B must be calculated from the geometrical sum of the currents -A and -C.
To do this, you can sum up the sample points or the Fourier coefficient.
The artificial neutral point does not allow measuring the voltage asymmetry exactly and is not
realized. The measured values are only exact, if you use a four-wire net with neutral point. Often
the three-wire net is used only to save the cable connection to current transformer 2. Only in this
case, it would be useful to measure the asymmetry.
50
⋅
I
1
64
1
∑
+
i
u
i
ν
ν
ν
ν
12
1
23
3
64
ν
=
1
1
64
−
π
1
∑
j
+
i
e
2
u
ν
ν
ν
12
1
23
64
ν
=
1
)
+
I
U
I
1
23
3
)
+
+
⋅
+
2
2
2
U
U
I
I
23
31
1
2
1
−
π
j
i
e
2
ν
3
+
2
2
I
3
Power Meter SICAM P 7KG7750/55, Manual
E50417-B1076-C340-A6, Edition 09.2013
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