GE Multilin EPM 2200, Инструкция по эксплуатации

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CHAPTER 1: THREE-PHASE POWER MEASUREMENT DELTA CONNECTION
EPM 2200 POWER METER – INSTRUCTION MANUAL 1–3
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.
1.3 Delta Connection
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.
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.
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.
7,620 volts 13,200 volts
Table 1.1: Common Phase Voltages on Wye Services
Phase to Ground Voltage Phase to Phase Voltage
V
C
Phase 1
Phase 3
Phase 2
V
A
V
B