Electro Industries 1252, Installation And Operation Manual

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1.1.2: Delta Connection
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Delta connected services may be fed with either three wires or four wires. In a three-phase delta
service the load windings are connected from phase-to-phase rather than from phase-to-ground.
Figure 1.3 shows the physical load connections for a delta service.
In this example of a delta service, three wires will transmit the power to the load. In a true delta
service, the phase-to-ground voltage will usually not be balanced because the ground is not at the
center of the delta.
Figure 1.4 shows the phasor relationships between voltage and current on a three-phase delta circuit.
In many delta services, one corner of the delta is grounded. This means the phase to ground voltage
will be zero for one phase and will be full phase-to-phase voltage for the other two phases. This is
done for protective purposes.
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Another common delta connection is the four-wire, grounded delta used for lighting loads. In this
connection the center point of one winding is grounded. On a 120/240 volt, four-wire, grounded
delta service the phase-to-ground voltage would be 120 volts on two phases and 208 volts on the
third phase. Figure 1.5 shows the phasor diagram for the voltages in a three-phase, four-wire delta
system.
Electro Industries/GaugeTech
Doc # E107706 V1.2 5
1-3
Phase A
Phase B
Phase C
Figure 1.3: Three-Phase Delta Winding Relationship
Vab
Vbc
Vca
Ia
Ib
Ic
Figure 1.4: Phasor Diagram, Three-Phase Voltages and Currents Delta Connected.