CHAPTER 2: ELECTRICAL BACKGROUND
FIGURE 2–2: Three-Phase Voltage and Current Phasors for Wye Winding
The phasor diagram shows the 120° 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.
The following table indicates the common voltages used in the United States for wye- connected systems.
Table 2–1: Common Phase Voltages on Wye Services
Phase-to-Ground Voltage | Phase-to-Phase Voltage |
| |
| |
120 volts | 208 volts |
| |
277 volts | 480 volts |
| |
2400 volts | 4160 volts |
| |
7200 volts | 12470 volts |
| |
7620 volts | 13200 volts |
| |
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. The neutral wire is typically tied to the ground or center point of the wye (refer to the Three-Phase Wye Winding diagram above).
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 the table above, 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.
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE | 2–3 |