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Posted by Tomi Engdahl (194.29.197.3) on October 21, 2003 at 01:30:33:
In Reply to: single/three phase posted by Said on October 21, 2003 at 00:19:12:
: Please advise me that what does three phase and single phase means in electricity
Single phase power has the mains voltage (typically 120V AC or 230V AC
depending on the country) between two wires: live and neutral.
The frequency of DC voltage is 50 or 60 Hz depending on the country.
Single-phase power is used in very many applications, for example
to power all typical home electrical appliances. You get single-phase
power from normal elecrical outlet in home. Distributing single-phase
power takes two wires: live and neutral. In some cases an extra
safety ground wires is used to provide increased user safety.
In three phase power system the generator the generates electricity
produces three voltages. Each voltage rises and falls at the same
frequency (50 Hz or 60 Hz depending on the country). However, the
phases are offset from each other 120 degrees.
Electrical utilities generate and transmit three-phase power.
Commercial electrical generators of any size generate three-phase AC power.
The 3-phase power leaves the generator and enters a transmission substation
at the power plant. Three phase power is commonly found in industrial
applications and electrical distribution. Three-phase electrical
generation is very common and is a more efficient use of conductors
than other systems. Three phase power is particularly useful in AC motors,
where it can be used to generate a rotating magnetic field easily
and efficiently. Practically all large electrical motors used
in heavy industry use three phase power.
Three phase power distribution saves copper for the following reason:
At the load end of the circuit the return legs of the three phase
circuits can be coupled together at the neutral point, where the three
currents sum to zero. This means that the currents can be carried
using only three cables, rather than the six that would otherwise be
needed. In practical applications the three phase power is wired
either with only three phase wires or three phase wires plus neutral
wire systems. In addition to those there can be a separate safety
ground wire.
Three phase 230V/400V: This is the standard way for three phase power
distribution in Europe to homes. The ouput from mains transformer is
Y-conneted. There is 230V AC from each phase to neutral and 400V AC
from phase to phase. The normal 230V electrical outlets are wired
between neutral and one phase. Large high power loads use all three
phases (the indivudual loads in such equipment can be phase to neutral
or phase to phase as needed).
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