ABB Relion SMU615 Technical Manual page 178

Section 7
Measurement functions
172
Some of the measurement functions operate on two alternative measurement modes:
"DFT" and "RMS". The measurement mode is selected with the X Measurement mode
setting. Depending on the measuring function if the measurement mode cannot be
selected, the measuring mode is "DFT".
Demand value calculation
The demand values are calculated separately for each measurement function and per
phase when applicable. The available measurement modes are "Linear" and
"Logarithmic". The "Logarithmic" measurement mode is only effective for phase
current and residual current demand value calculations. The demand value calculation
mode is selected with the setting parameter Configuration/Measurements/A
demand Av mode. The time interval for all demand value calculations is selected
with the setting parameter Configuration/Measurements/Demand interval.
If the Demand interval setting is set to "15 minutes", for example, the demand values
are updated every quarter of an hour. The demand time interval is synchronized to the
real-time clock of the merging unit. When the demand time interval or calculation
mode is changed, it initializes the demand value calculation. For the very first demand
value calculation interval, the values are stated as invalid until the first refresh is
available.
The "Linear" calculation mode uses the periodic sliding average calculation of the
measured signal over the demand time interval. A new demand value is obtained once
in a minute, indicating the analog signal demand over the demand time interval
proceeding the update time. The actual rolling demand values are stored in the
memory until the value is updated at the end of the next time interval.
The "Logarithmic" calculation mode uses the periodic calculation using a log10
function over the demand time interval to replicate thermal demand ammeters. The
logarithmic demand calculates a snapshot of the analog signal every 1/15 x demand
time interval.
Each measurement function has its own recorded data values. In merging unit, these
are found in Monitoring/Recorded data/Measurements. In the technical manual
these are listed in the monitored data section of each measurement function. These
values are periodically updated with the maximum and minimum demand values. The
time stamps are provided for both values.
Reset of Recorded data initializes a present demand value to the minimum and
maximum demand values.
Value reporting
The measurement functions are capable of reporting new values for network control
center (SCADA system) based on various functions.
• Zero-point clamping
• Deadband supervision
• Limit value supervision
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SMU615
Technical Manual