38 Function Description
WAGO I/O System 750 XTR
750-495/040-010 3-Phase POM 20KV 300A XTR
Manual
Version 1.0.0
Figure 7: RMS Calculation (Example – Not to Scale)
The current and voltage RMS values are calculated for each period in the I/O
module. The RMS values can be exported with every second period with the
specified measuring accuracy via the process image (2T). In a 50 Hz power
system, this corresponds to a refresh rate of 40 ms.
The
arithmetic mean value
for the phase current and voltage is calculated on
the basis of the RMS values. The time interval for which the mean value should
be calculated can be set via WAGO-I/O-
CHECK
or parameters 34, 35 and 36.
The
minimum and maximum RMS values
for the current and voltage are also
determined over a configurable time interval (WAGO-I/O-
CHECK
or parameters
37, 38 and 39).
Peak values
for current and voltage can also be recorded for a selectable phase.
The specified observation interval for this can be set using the number of half-
waves (WAGO-I/O-
CHECK
or registers 43, 44 and 45).
Calculation of line-to-line voltages is performed on the basis of the phase
voltages and the corresponding phase angles.
Calculation of Power
Individual, synchronous sampling values for current and voltage are used for
calculating active power (P). Phase shifts between the currents and voltages are
taken into account in the power calculation. Positive values occur when the
power is “exhausted” by a load, i.e., the current has a phase shift of −90° … +90°
relative to the voltage (operation under load, quadrants I and IV). Negative values
occur when the power is “fed in” by a generator, i.e., the current has a phase shift
of 90° … 270° relative to the voltage (generator operation, quadrants II and III).
See the figure “4-Quadrant Representation of Active and Reactive Power.”