120.00 *
* 2.793 * SIN (30
°
+30
°
) + 120.00 *
* 2.793 * SIN (30
°
- 30
°
)
then, 502.7397 + 0 = 502.74 VAR
Note: For apparent power, VA, transducers, the calculations remain the
same, except there are no COS or SIN functions.
For the example above,
120.00 *
* 2.793 + 120.00 *
* 2.793 = 1161.03 VA
3.8.10.7.5
Watt/VAR 2 1/2 Element
This transducer is normally used in three-phase, four wire Wye applications, which
requires 2 voltages and 3 currents to test. The two voltages and three currents are all
refernced to ground. The MPRT will automatically select two voltage and three current
channels,
V1
,
V3
,
I1, I2
and
I3
. The test will initially start at the default voltage value, that
is set in the
Default Setting Screen
, for each Voltage output. Thus, for a default voltage
setting of 120 volts, V1 will be set to 120 Volts at an angle of 0
°
, and V3 will be 120 Volts
at 240
°
lagging. This assumes that the default phase angle is 0 - 360 Degrees lag, and
not +/- 180 degrees. If the +/- 180 degree phase angle option is used, then V3 will be at
+120
°
. I1and I3 will be in-phase with their respective voltages, or I1 at 0
°
and I3 at 240
°
lag (or + 120
°
). I2 will be at 120
°
lag (or -120
°
). When the user inputs the
MAX.
Watts
value in the
Transducer Setting Screen
, the firmware can calculate the required test
currents for full scale value.
The formula required to calculate Watts for 2 1/2 Element transducer is,
V1 * I1 * (COS
∅
) + V3 * I3 * (COS
∅
) + V1 * I2 * (COS 60
°
+
∅
) + V3 * I2 * (COS 60
°
-
∅
) = Total Watts
Where
∅
is the incremental angular change between V1 and I1 and V3 and I 3, with I2
changing at the same incremental angle as I1 and I3..
Example: The default voltage is 120.00 Volts AC, and the user inputs 1500 Watts as
Max. Value. The current required for full scale output from the transducer is,
120 * I1 * COS 0
°
+ 120 * I3 * COS 0
°
+ V1 * I2 * (COS 60
°
+0
°
) + V3 * I2 *
(COS 60
°
- 0
°
) = 1500 Watts
I1 = 500 Watts/(120 Volts * COS 0
°
) , or I1 = 500/120
then I1, I2 and I3 will be 4.1667 Amperes each
Therefore, when the user inputs 1500 Watts in the
MAX
. value window, the test set
should automatically show a test current value for I1 of 4.167 Amperes at an angle of 0
°
,
I2 will be 4.167 at 120
°
(-120
°
) and I3 will be 4.167 Amperes at an angle of 240
°
(+120
°
).
Note that the current is rounded up to 7 in the last digit displayed.
When the test is Started, the measured voltage and current outputs are displayed and the
calculated Watts is based on the measured voltage and current outputs. This is the value
that gets displayed in the
Transducer Test Screen
under the
MPRT Output
, next to the
-
147
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