3 phase
electricity systems may or may not have a neutral wire. A
neutral wire allows the three phase system to use a
higher voltage while still supporting lower voltage
single phase appliances. In high voltage distribution
situations it is common not to have a neutral wire as
the loads can simply be connected between phases
(phase-phase connection).
3 Phase
Electricity Wiring Color Coding
The
3 phases are typically indicated by colors which
vary by country. See the table for more information.
Conductors
of a three phase system are usually identified by a
color code, to allow for balanced loading and to
assure the correct phase rotation for induction
motors. Colors used may adhere to old standards or to
no standard at all, and may vary even within a single
installation. However, the current National Electrical
Code (2005) does not require any color identification
of conductors other than that of the neutral (white or
white with a color stripe) the ground (green or green
with a yellow stripe) or in the case of a High Leg
Delta system, the High Leg must be identified orange.
Read more on 3 Phase Wiring and Color Coding.
3 Phase
Electricity Generation
At
the power station, an electrical generator converts
mechanical power into a set of alternating electric
currents, one from each electromagnetic coil or
winding of the generator. The currents are sinusoidal
functions of time, all at the same frequency but with
different phases. In a three-phase system the phases
are spaced equally, giving a phase separation of
120°. The frequency is typically 50 Hz in Europe and
60 Hz in the US (see List of countries with mains
power plugs, voltages and frequencies).
3 Phase
Electricity Distribution and Transmission
After
numerous further conversions in the transmission and
distribution network the power is finally transformed
to the standard mains voltage (the voltage of
"house" or "household" current in
American English). The power may already have been
split into single phase at this point or it may still
be 3 phase. Where the step-down is 3 phase, the
output of this transformer is usually star connected
with the standard mains voltage (120 V
in North America and 230 V in Europe) being the
phase-neutral voltage. Another system commonly seen in
the USA is to have a delta connected secondary with a center
tap on one of the windings supplying the ground
and neutral. This allows for 240 V three phase as well
as three different single phase voltages (120 V
between two of the phases and the neutral, 208 V
between the third phase (known as a wild leg) and
neutral and 240 V between any two phases) to be made
available from the same supply.
3 Phase
Electricity Calculation
The
3 phases are typically indicated by colors which
vary by country. See the table for more information.
3 Phase
Electricity Loads
The
most important class of three-phase load is the
electric motor. A three phase induction motor has a
simple design, inherently high starting torque, and
high efficiency. Such motors are applied in industry
for pumps, fans, blowers, compressors, conveyor
drives, and many other kinds of motor-driven
equipment. A three-phase motor will be more compact
and less costly than a single-phase motor of the same
voltage class and rating; and single-phase AC motors
above 10 HP (7.5 kW) are uncommon.
Large
air conditioning equipment (for example, most York
units above 2.5 tons (8.8 kW) cooling capacity) use
three-phase motors for reasons of efficiency and
economy.
Resistance
heating loads such as electric boilers or space
heating may be connected to three-phase systems.
Electric lighting may also be similarly connected.
These types of loads do not require the revolving
magnetic field characteristic of three-phase motors
but take advantage of the higher voltage and power
level usually associated with three-phase
distribution.
Large
rectifier systems may have three-phase inputs; the
resulting DC current is easier to filter (smooth) than
the output of a single-phase rectifier. Such
rectifiers may be used for battery charging,
electrolysis processes such as aluminum production, or
for operation of DC motors.
An
interesting example of a three-phase load is the
electric arc furnace used in steel making and in
refining of ores.
In
much of Europe stoves are designed to allow for a 3 phase
feed. Usually the individual heating units
are connected between phase and neutral to allow for
connection to a single phase supply where this is all
that is available.
3 Phase
Loads on 1 Phase
Power
The
three phases are typically indicated by colors which
vary by country. See the table for more information.
3 Phase
Converters
Occasionally
the advantages of three-phase motors make it
worthwhile to convert single-phase power to 3 phase. Small customers, such as residential or farm
properties may not have access to a three-phase
supply, or may not want to pay for the extra cost of a
three-phase service, but may still wish to use
three-phase equipment. Such converters may also allow
the frequency to be varied allowing speed control.
Some locomotives are moving to multi-phase motors
driven by such systems even though the incoming supply
to a locomotive is nearly always either DC or single
phase AC.
Because
single-phase power is interrupted at each moment that
the voltage crosses zero but three-phase delivers
power continuously, any such converter must have a way
to store energy for the necessary fraction of a
second.
One
method for using three-phase equipment on a
single-phase supply is with a rotary phase converter,
essentially a three-phase motor with special starting
arrangements that produces a three-phase system. When
properly designed these rotary converters can allow
satisfactory operation of three-phase equipment such
as machine tools on a single phase supply. In such a
device, the energy storage is performed by the
mechanical inertia (flywheel effect) of the rotating
components.
Some
devices are made which create an imitation three-phase
from three-wire single phase supplies. This is done by
creating a third "subphase" between the two
live conductors, resulting in a phase separation of
180° - 90° = 90°. Many three-phase devices will run
on this configuration, but at lower efficiency.
Solid-state
inverters also can be used to power three-phase motors
from a single-phase supply.
The
two main types of 1 phase to 3 phase converters are
Rotary Phase Converters and Static Phase Converters.
3 Phase
Frequency and Frequency Converters
The
three phases are typically indicated by colors which
vary by country. See the table for more information.
The two main types of 1 phase to 3 phase converters
are Rotary Phase Converters and Static Phase
Converters.
1 Phase
Loads on 3 Phase
Power
Single-phase
loads may be connected to a three-phase system, either
by connecting across two live conductors (a
phase-to-phase connection), or by connecting between a
phase conductor and the system neutral, which is
either connected to the center of the Y (star)
secondary winding of the supply transformer, or is
connected to the center one winding of a delta
transformer (High leg Delta system). Single-phase
loads should be distributed evenly between the phases
of the three-phase system for efficient use of the
supply transformer and supply conductors.
Additional 3 Phase
Generator Information Sources:
Diesel
Generators
•
Diesel Power Generators
•
Diesel
Generator Sets
•
Power
Generators
•
Onan Diesel Generators
•
Kipor Diesel Generator
•
Kubota Diesel Generator
•
Cummins Diesel Generator
•
Yanmar Diesel Generator
Continue
And Read About Additional 3 Phase Power Details:
3 Phase Contents
