7
Using the 1040C for Calibrating Polyphase Devices
A.C. Voltage
Commercially available multi-phase
voltage transducers frequently consist of
more than one single-phase model from the
manufacturers product line, repackaged into
a common enclosure. In many cases, the
outputs remain separate and independent.
The procedure for calibration of these types
of transducers is virtually identical to that of
the single-phase voltage transducer. The
three elements can be connected in parallel
across the voltage output of the 1040C, as
shown in figure 7a, provided that the
combined current demand of the elements
does not exceed the burden capability of the
1040C (refer to table 1.2 in the operation
manual). Multiple voltmeters may also be
connected to the 1040C in the same manner,
as shown in figure 7b, with the same total
current burden restriction.
A.C. Current
Like their ac voltage counterparts,
commercially available multi-phase current
transducers frequently consist of more than
one single-phase model from the
manufacturers product line, repackaged into
a common enclosure. In many cases, the
outputs remain separate and independent.
The procedure for calibration of these types
of transducers is nearly identical to that of
the single-phase current transducer. The
three elements can be connected (in series)
across the current output leads of the 1040C,
as shown in figure 8a, provided that the
combined voltage drop across the elements
does not exceed the burden capability of the
1040C (refer to table 1.1 in the operation
manual). Multiple current meters may also
be connected to the 1040C in the same
manner, as shown in figure 8b, with the same
total voltage burden restriction.
A.C. Power
Power measurement in a three-phase,
four-wire system requires three complete
watt meters or watt transducers (each watt
meter or transducer consists of one current
element and one voltage element). Figure 9a
shows a typical connection diagram for
measurements of this type. A current sensing
element is placed in series with each of the
three phases, and a voltage sensing element
is connected between each of the phases and
the neutral wire. It is unnecessary to
measure the neutral current directly, since
any current flowing in the neutral conductor
will be simultaneously flowing in one or
more of the phases and will thus be
measured.
Power measurement in a three-phase,
three
-wire system requires
two
complete watt
meters or watt transducers. Figure 9b shows
a connection diagram for this type of
measurement. Again, the number of current
elements required is equal to one less than
the number of current-carrying conductors,
since any current in the non-instrumented
conductor must simultaneously be flowing in
one or both of the others. The voltage
elements are connected to the two phases
having the current elements, with the
common point for the voltage elements being
the third phase.
Calibration of multi-element watt
transducers or meters can be accomplished
using the setup shown in figure 10.
Basically, all of the current elements would
be connected in series and placed across the
current output of the 1040C, and all of the
voltage elements would be connected in
parallel and placed across the voltage output
of the 1040C. Again, current and potential
transformers are shown for reference.
Phasing of the elements is of great
