2)
Substituting Equation (11.Polyphase three-phase electrical systems
227
Now for star connection,
V
V
I I
P
L
L P
and
(11.
.1), have:
Total three-phase power cos (W)
L φ
Now consider delta connection:
V I
I
P P
L
and
(11.2) into Equation (11.
.1) have, for any balanced
three-phase load,
Total three-phase power cos (W)
L φ
so, general Equation for three-phase power is:
Power cos
L L
3 φ
Example 1
A balanced star-connected three-phase load 10Ω per phase supplied from 400V, 50Hz
mains supply unity power factor. Calculate (a) the phase voltage, (b) the line current and (c)
the total power consumed.3) into Equation (11.
For (b),
I I
V
R
I I
L P
P
P
L P
(A)
V
A
230 9
10
23 09
.
For star connection,
V I
L P
and
3
For (a),
V
V
V
P
L
P
(V)
V
V
3
400
1 732
230 9
.3)
Substituting Equation (11.
Ω
For (c),
Power cos (W)
Power kW
L L
3
1 732 400 16
V φ
∴
