Environmental Engineering Reference
In-Depth Information
Star
connection
Delta
connection
Figure 5.22
Principle of Star and Delta Connections
For a distance
x
along the circumference, the temporal and spatial staggered
magnetic induction
B
with the amplitude
B
becomes:
(5.69)
The six connections U1, U2, V1, V2, W1 and W2 of the three windings are
connected either to a star or to a delta connection as shown in Figure 5.22.
This reduces the number of external connections to the three phases L1, L2
and L3. These three phases are often also called R, S and T. The neutral
conductor N can be added as reference; however, a neutral or zero conductor
is not necessary for three-phase machines.
The rms values of the phase-to-phase voltages and the phase to neutral
conductor voltages are related as follows:
(5.70)
In the European grid, the rms value of the voltage between phase and neutral
conductors is 230 V and between two phases
√
3
•
230 V = 400 V. All voltages
are phase-shifted by 2
/3.
For the
star connection
, the voltages
V
Y
at the windings are equal to the
corresponding phase-to-neutral conductor voltages. The voltages
V
D
at the
windings of a
delta connection
are equal to the phase-to-phase voltages
V
.
Hence, the connection between the rms voltages is:
π
(5.71)
The currents
I
Y
in the windings of a star connection are the same as in the
phases
I
:
(5.72)