Volt-Amps And Volt-Amps Reactive - Arbiter Systems 1040C Manual

and multi-phase watt transducers.
case, the transducer is connected in the same
manner as a conventional watt transducer
(refer to figures 5 and 6).
Typical applications of power factor
meters for single-phase systems involve
circuit connections which are similar, if not
identical to those employed by single phase
watt and var meters.
representative circuit
connection diagrams for these meters are
shown in figures 5 and 6. When connected
per the calibration setup diagram, calibration
of single-phase power factor meters can be
performed using one of the methods given
above, and in accordance with the meter
manufacturer's recommendations. For more
detailed instructions on operating the 1040C
for calibration of power factor, refer to
section 2.5.1 of the operation manual.

Volt-Amps and Volt-Amps Reactive

Volt-Amps is the product of the rms
voltage and the rms current in a circuit,
without regard to the phase angle between
them. Another term commonly used to
describe this parameter is apparent power. If
a separate rms ammeter and rms voltmeter
were used to measure the current and
voltage, respectively, and the two values
were multiplied together, the result would be
the apparent power. This is not an indication
of the amount of work that can be done,
however; if the phase angle is 90 degrees
(power factor is zero), the true power
available is zero.
Volt-amps reactive (SI unit=var) is the
same as volt-amps, but with the phase angle
between voltage and current factored in.
Vars are a measure of the amount of power
required by the reactive portion of a load,
and actually represents circulating current in
the circuit. Vars are calculated as the
product of the RMS voltage, the RMS
current, and the sine of the phase angle
In this
In light of this,
and calibration
5
between the two. For an illustration of the
relationship between phase angle and vars
when using the 1040C, refer to figure 12.
The 1040C has a provision for displaying
and modifying both volt-amps and vars;
successively pressing the "Power" key during
operation will first display watts, then vars,
then volt-amps. The user can continue
indefinitely to scroll through these three
choices.
Some points of interest regarding va and
var measurements:
It is important to note that unless there is
a phase angle of greater than zero
between voltage and current, the var
value will be zero. Also, since va and var
indications are sub-functions of the
power mode, adjustment of these values
using direct entry, the control knob, or
the up/down keys affects the value by
changing only the current, not the voltage
or the phase angle. The current can only
be modified to a point within the current
range of the 1040C.
current exceeds this range, the display
will indicate "Entry Error". Additionally,
if the phase angle is set to zero and the
user attempts to enter any var value other
than zero, "Entry Error" will be indicated.
This is because under these conditions,
no value of voltage or current will
produce anything other than zero vars.
Typical applications of va and var meters
or transducers for single-phase systems
involve circuit connections
similar, if not identical to those employed by
single phase watt and power factor meters
and transducers. Therefore, representative
circuit connections
connections for these devices are shown in
figures 5 and 6, respectively.
connected per the calibration setup diagram,
calibration of these instruments can be
performed in accordance with the meter
manufacturer's recommendations. For more
If the necessary
which are
and calibration
When