GE EPM6000 Instruction Manual page 10

THREE-PHASE SYSTEM CONFIGURATIONSCHAPTER 1: THREE-PHASE POWER MEASUREMENT
Ia
A
Iab
Vab
Ib
B
Vca
Ica
Vbc
Ibc
Ic
C
FIGURE 1–3: Three-phase Delta Winding Relationship
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.
The following diagram 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.
Vca
Ic
Vbc
Ia
Ib
Vab
FIGURE 1–4: Three-Phase Voltage and Current Phasors for Delta Winding
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. The phasor diagram for the voltages in a three-
phase, four-wire delta system is shown below.
1–4 EPM6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE