Electronic Wattmeter
Chapter
2
3
phase
{~~'--~t_..--1
Balanced
supply 8 Load
:-"---L_.::.:::.:::..:::___J
Fig 2.5 Power and power factor
in
a balanced load system
Unbalanced system
If either the load or the supply is unbalanced (or both) it is
necessary to obtain the power as the sum of readings, taken
with the current terminals connected
in
series with each line
in
turn, except one, and the voltage connection is taken to that
one
in
each case. Connections are shown
in
fig
2.6 for three-wire
and four-wire three-phase systems.
If only one wattmeter is
available it may
be
connected
in
each of the positions shown
in
turn. The power is the sum of all the readings. (This scheme
of
connections
can
be
extended
to
any number of wires, taking n -
1 readings
in
the n - wire case. Also it is not
in
principle
restricted
to
any particular current or voltage waveforms).
,-----l
1
load
1
I
I
I
I
I
I
I
I
I
L
_____
_j
Fig 2.6a Measuring power
in
a three-terminal load
1 5
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