Zero Clamping - ABB RET670 Applications Manual

Section 3
IED application
3.15.1.2
750
The power system quantities provided, depends on the actual hardware,
(TRM) and the logic configuration made in PCM600.
The measuring functions CMSQI and VMSQI provide sequence component quantities:
• I: sequence currents (positive, zero, negative sequence, magnitude and angle)
• V: sequence voltages (positive, zero and negative sequence, magnitude and angle).
The CVMMXN function calculates three-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.

Zero clamping

The measuring functions, CMMXU, VMMXU, VNMMXU and CVMMXN have no
interconnections regarding any setting or parameter.
Zero clampings are also entirely handled by the ZeroDb for each and every signal
separately for each of the functions. For example, the zero clamping of U12 is handled
by UL12ZeroDb in VMMXU, zero clamping of I1 is handled by IL1ZeroDb in
CMMXU ETC.
Example how CVMMXN is operating:
The following outputs can be observed on the local HMI under Monitoring/
Servicevalues/SRV1
S Apparent three-phase power
P Active three-phase power
Q Reactive three-phase power
PF Power factor
ILAG I lagging U
ILEAD I leading U
U System mean voltage, calculated according to selected mode
I System mean current, calculated according to selected mode
F Frequency
The settings for this function is found under Setting/General setting/Monitoring/
Service values/SRV1
1MRK504116-UUS C
Application manual