power carrying conductor (hot wire)
that each phase receives exactly the
and the neutral (ground) wire or among
same load.
In practically all TO
several power carrying wires.
installations
some
difference
in
loading will exist among the different
a. Phase loading.
When a load is
phases, However, the loadings on the
connected between a hot wire and a
generator must be balanced as much as
neutral wire the power is assumed to
possible, and at the very least,
be supplied completely by the hot
within 10 percent, for the reasons
wire.
Likewise, a load connected
stated in b above.
Thus the total
between two or more hot wires is
power delivered by the generator in
distributed equally among the hot
the maximum loaded phase must be less
wires.
Many loads may be connected
than or equal to 1.1 times the power
among various hot wires in a given
delivered in the minimum loaded phase.
distribution system.
For example, in
Although this amount of unbalance is
within acceptable limits, it is still
an installation fed by a 3 4W
considered a relatively high degree of
generator, single phase loads may be
unbalance.
The
more
generator
attached
to
the
different
phases
unbalance in a system, the greater the
throughout the system.
However, no
chances of causing the bad effects
matter how many loadings are supplied,
mentioned earlier.
An attempt should
or in what arrangement they may be,
always
be
made
to
balance
the
the generator responds to the total
generator within 1 percent, so that
load on each of its phases and
the power delivered in the maximum
attempts to supply the required power
loaded phase is less than or equal to
to satisfy the particular load in each
1.01 times the power delivered in the
phase.
minimum loaded phase.
Accomplishment
of this objective is often a tedious
b. Phase balance. It is imperative
trial and error procedure, but it is
that the power in each phase just as
not impossible, and it becomes less
it leaves the generator be balanced;
difficult
as
the
size
of
the
that is, each phase receive the same
installation increases.
A determined
amount of power from the generator.
effort
should
always
be
made
to
This will only come about as a result
achieve
this
degree
of
generator
of having equal total loadings on each
balance.
of the phases, and the layout must be
designed to achieve this.
Unbalanced
4.
BALANCING SINGLE-PHASE SYSTEMS
loading has the following three bad
effects:
A 1 2W system is the basic load
(1) Output.
It
will
be
carrying
circuit
and
cannot
be
impossible to get full output out of a
unbalanced since there are only two
lightly
loaded
phase
without
wires, which can only be connected to
overloading the others.
The 1 3W 120/240V
one load group.
system, however, contains two hot
(2) Voltage regulation.
System
wires and a neutral which means that
voltage regulation becomes poor since
two single phase 120V load groups
unbalancing causes high voltage on the
and/or one single phase 240V load
lightly loaded phase and low voltage
group may be served.
When designing
on the others.
such a system, the two single phase
120V
load
groups
should
be
of
(3) Damage.
Prolonged unbalance
approximately equal size.
will damage generating equipment.
5.
BALANCING THREE-PHASE SYSTEMS
c. System balance.
In practice it
is highly improbable that it will be
A 3 3W 208V system contains three hot
possible
to
balance
the
various
wires, meaning that three single-phase
loadings in an actual installation so
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