6
Star and delta connections.
Three-phase power
We know from our single-phase alternating current theory Chapter 10
that power can found from the following formula:
Power cos (W)
φ
In any balanced three-phase system, the total power equal three times
the power any one-phase.
Making star connection the local sub-station has the advantage that
two voltages become available line voltage 400 between any two
phases, and phase voltage 230 between line and neutral which is
connected the star point. The star point the distribution transformer earthed because
earth also zero potential.Basic Electrical Installation Work
226
connect the windings most three-phase motors because the phase
windings are perfectly balanced and, therefore, not require neutral
connection.
.1)
IL
IL IL
VL VL
IP
IL
IL
IL
IP
VP
IP IP
IP IP
N
VP
VL VP
Star IP
connection:
Delta IP
VL VP
connection:
FIGURE 11.
In any star-connected system currents flow along the lines (IL), through the
load and return the neutral conductor connected the star point.
∴ Total three-phase power cos (W)
P (11. a
balanced three-phase system all currents have the same value and when
they are added phasor addition, find the resultant current is
zero. star-connected system also called a
three-phase four-wire system and allows connect single-phase loads
to three-phase system. Therefore, current flows the neutral and the star point zero
volts
