Doc# E145701 1-3
1: Three-Phase Power Measurement
Electro Industries/GaugeTech
The Leader In Power Monitoring and Smart Grid Solutions
Electro Industries/GaugeTech
The Leader In Power Monitoring and Smart Grid Solutions
The phasor diagram shows the 120
o
angular separation between the phase voltages.
The phase-to-phase voltage in a balanced three-phase wye system is 1.732 times the
phase-to-neutral voltage. The center point of the wye is tied together and is typically
grounded. Table 1.1 shows the common voltages used in the United States for wye-
connected systems.
Usually a wye-connected service will have four wires: three wires for the phases and
one for the neutral. The three-phase wires connect to the three phases (as shown in
Figure 1.1). The neutral wire is typically tied to the ground or center point of the wye.
In many industrial applications the facility will be fed with a four-wire wye service but
only three wires will be run to individual loads. The load is then often referred to as a
delta-connected load but the service to the facility is still a wye service; it contains
four wires if you trace the circuit back to its source (usually a transformer). In this
type of connection the phase to ground voltage will be the phase-to-ground voltage
indicated in Table 1, even though a neutral or ground wire is not physically present at
the load. The transformer is the best place to determine the circuit connection type
because this is a location where the voltage reference to ground can be conclusively
identified.
Phase to Ground Voltage Phase to Phase Voltage
120 volts 208 volts
277 volts 480 volts
2,400 volts 4,160 volts
7,200 volts 12,470 volts
7,620 volts 13,200 volts
Table 1: Common Phase Voltages on Wye Services
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