5044 B U Bowman Dr #102 ::: Buford, Georgia 30518
e-mail firstname.lastname@example.org ::: Phone: 678.546.6780
Delta (Corner Ground)
Delta (High Leg)
|2-Wire, Single Phase|
3-Wire, Single-Phase System
The most common source of single-phase power in facilities is by generation from a single-phase generator or received from the utility as a single phase source. (shown right):
| Another method is by utilization of one phase of a three-phase power source.|
In a three-phase system each phase of the distribution system is a single phase spaced 120 degrees from the other two, and this makes a three phase source of power convenient and practical to use as a source of single phase power.
Many commercial systems will be a combination of single-phase and three loads derived from a three-phase source.
| The simplest three-phase system is the 3-wire Delta configuration, normally used for transmission of power in the intermediate voltage class from approximately 15,000 volts to 600 volts.|
It is also used in industrial facilities by grounding one "corner" of the System.
The corner-grounded Delta system has an obvious economy in wiring costs, and the grounded phase can be used to physically protect the other two phases from accidental grounding or lightning strikes in outdoor settings.
The disadvantage is that it does not allow for a provision to "spawn" single-phase panels.
There are several strict precautions that must be observed in the operation of this system:
First, all loads must be carefully balanced on both the single-phase and three-phase legs.
Second, because the voltage between one leg and the grounded neutral is considerably higher than the rest of the single-phase system, a measurement between the neutral and the phase must be taken to identify the "high leg," or "bastard voltage." The standard is for the "high leg" to be identified using an orange wire, or an orange marking at the wire termination. Most often, it is located between the two lower voltage conductors.
Finally, the "high leg" is never used as a single-phase source because no ground or grounded neutral exists for this circuit.
| The "Wye" system is different in that the ground voltage or voltage available from phase to ground is the phase voltage divided by 1.73.|
Depending on the selection of conductors, one of the following is available: a reducedvoltage single phase between a phase leg and the neutral; a full-voltage single-phase circuit between any two phase legs; or a full-voltage three-phase power.
Again, some precautions must be taken when balancing the single-phase loads in the system. The full load ampacity of the neutral must be sized to 1.73 times the highest phase ampacity. This is done to avoid either an over-current condition if a fault is present or the operation of single-phase loads at reduced voltage if the loads become severely unbalanced by accidental interruption.
Outside of the United States, the same three-phase configurations can be found...but there are a variety of voltages used. Often, industrial locations will even have voltage configurations that are different from the host country's "standard" configuration to accommodate foreign equipment.
This system is different from the US "Edison System" in that only one voltage is available.
PHONE: (678) 546-6780 FAX: (678) 546-6782
5044 B U Bowman Drive #102
Buford, Georgia 30518
PHONE: (678) 546-6780
Last Updated: 07 Jun 2004
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