Label of
Watt 2 1/2 Element
. Another value of Watts gets calculated using the
measured dc Volts or dc milliampere output as displayed in the
Transducer Output
section. Let us assume that in our example transducer, the output is in dc milliamperes.
In this example, let 20 milliamps of dc current be equal to the full scale output of 1500
Watts. For this example, let's say that the measured output voltages are 120.02 Volts (V1
and V3) and the measured output currents are 4.166, Amperes. The measured output
Watts would be,
120.02 * 4.166 * 0
°
+120.02 * 4.166 * COS 0
°
+ 120.02 * 4.166 * (COS 60
°
+0
°
) + 120.02 * 4.166 * (COS 60
°
- 0
°
) =
or, 500.0332 + 500.0332 + 250.0166 + 250.0166
1500.10
Watts
For this example, let's assume the measured output current from the transducer is 20.1
mA dc. Based on a Max. value of 20 mA equals 1500 Watts, the displayed
Watts
in the
Transducer Output
section of the
Transducer Test Screen
should read
1507.5 Watts
The
Accuracy
displayed in the
Transducer Output
section would be equal to the
following,
(1507.5 - 1500.10 / 1500.10) * 100 = % accuracy or
0.493%
If this were a 0.5 % transducer, then the firmware would compare the accuracy values
between the Setting Screen and the Test Screen and would display
PASS
in the
Transducer Output
section of the test screen.
If the user adjusts the phase angle in the lagging direction by 30
°
, then the Watts output
changes.
Using the formula,
V1 * I1 * (COS
∅
) + V3 * I3 * (COS
∅
) + V1 * I2 * (COS 60
°
+
∅
) + V3 * I2 * (COS 60
°
-
∅
) = Total Watts
Where
∅
is the incremental angular change of 30
°
between V1 and I1 and V3 and I 3
etc. ,
then,
120 * 4.1667 * COS 30
°
+ 120 * 4.1667 * COS 30
°
+ 120 * 4.1667 * (COS 60
°
+30
°
) + 120 * 4.1667 * (COS 60
°
- 30
°
) = 1299.05 Total Watts
Note: All of the calculations are very similar when testing VAR 2 1/2
Element transducers.
The primary difference is replacing the COS function with the SIN
function. For the example above,
120 * 4.1667 * SIN 30
°
+ 120 * 4.1667 * SIN 30
°
+ 120 * 4.1667 * (SIN 60
°
+30
°
) + 120
* 4.1667 * (SIN 60
°
- 30
°
) = 1250.01 VAR's
-
148
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