easy overview of the present status of the power system. Additionally, it can be
used during testing and commissioning of protection and control IEDs in order to
verify proper operation and connection of instrument transformers (CTs and VT
s).
During normal service by periodic comparison of the measured value from the IED
with other independent meters the proper operation of the IED analog measurement
chain can be verified. Finally, it can be used to verify proper direction orientation
for distance or directional overcurrent protection function.
Several instances of each type of measurement function blocks are
available in the IED. The actual reported values from the IED are
dependent on the logic configuration made in PCM600.
All measured values can be supervised with four settable limits:
•
low-low limit
•
low limit
• high limit
• high-high limit
A zero clamping reduction is also supported, that is, the measured value below a
settable limit is forced to zero which reduces the impact of noise in the inputs.
Dead-band supervision can be used to report the measured signal value to the
station level when a change in the measured value is above the set threshold limit
or time integral of all changes since the last time value updating exceeds the
threshold limit. The measure value can also be based on periodic reporting.
All measurement functions uses fundamental frequency phasors (i.e. DFT filtering)
for internal calculations and for reporting of measured values. However, from the
following three measurement functions CMMXU, VMMXU and VNMMXU it is
also possible to report the total measured quantity (i.e. true RMS filtering). By
selecting the RMS mode, the reported value will in addition to the fundamental
magnitude also include harmonics. The RMS measurement is often required for
railway power systems which are typically polluted by harmonics.
The measurement function CVMMXN is located under: Main menu/
Measurement/Monitoring/Service values/CVMMXN
CVMMXN provides the following power system quantities:
• P, Q and S: two or single phase active, reactive and apparent power
• PF: power factor
• F: power system frequency
The CVMMXN function calculates two-phase power quantities by using
fundamental frequency phasors (DFT values) of the measured current respectively
voltage signals. The measured power quantities are available either, as
instantaneously calculated quantities or, averaged values over a period of time (low
pass filtered) depending on the selected settings.
Section 15 1MRK 506 375-UEN A
Monitoring
380 Railway application RER670 2.2 IEC
Application manual
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