Power Calculation - Allen-Bradley Rockwell Automation 857 User Manual

5-6
Measurement Functions

Power Calculation

857-UM001A-EN-P – July 2009
•
"1LL+U /LLy"
0
This mode is used with the synchrocheck function. See
Table 3.40.
•
"2LL/LLy"
This mode is used with the synchrocheck function. See
Table 3.40
•
"LL/LLy/LLz"
This mode is used with the synchrocheck function. See
Table 3.40.
The overvoltage protection is always based on the line-to-line
voltage regardless of the measurement mode.
The power calculations in Allen-Bradley devices are dependent on
the voltage measurement mode (see "Voltage Measurement Mode").
The equations used for power calculations are described in this
chapter.
The device is connected to line-to-line voltages
When the device is connected to line-to-line voltages, the voltage
measurement mode is set to equal to "2LL+Uo". The following Aron
equation is used for power calculation.
= ⋅ − ⋅
*
S U I U
12 L 1 23
= Three phase power phasor
S
= Measured voltage phasor corresponding the
U
12
fundamental frequency voltage between
phases L1 and L2.
* = Complex conjugate of the measured phase L1
I
1 L
fundamental frequency current phasor.
= Measured voltage phasor corresponding the
U
23
fundamental frequency voltage between
phases L2 and L3.
= Complex conjugate of the measured phase L3
*
I
L 3
fundamental frequency current phasor.
Apparent power, active power and reactive power are calculated as
follows:
=
S S
=
P real ( S )
=
Q imag ( S )
P
ϕ
=
cos
S
*
I
, where
L 3