Zero Clamping - Hitachi Relion 670 Series Applications Manual

1MRK511407-UUS Rev. N
• P, Q and S: three phase active, reactive and apparent power
• PF: power factor
• V: phase-to-phase voltage magnitude
• I: phase current magnitude
• F: power system frequency
,
The measuring functions CMMXU, VMMXU and VNMMXU provide physical quantities:
• I: phase currents (magnitude and angle) (CMMXU)
• V: voltages (phase-to-ground and phase-to-phase voltage, magnitude and angle) (VMMXU,
VNMMXU)
Fundamental frequency filtered values (DFT) or true RMS values can be selected as a measurement
type in CMMXU, VMMXU and VNMMXU functions.
The CVMMXN function calculates three-phase power quantities by using fundamental frequency phasors
(DFT values) of the measured current and 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.
It is possible to calibrate the measuring function above to get better then class 0.5 presentation. This is
accomplished by angle and magnitude compensation at 5, 30 and 100% of rated current and at 100% of
rated voltage.
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).
16.1.4

Zero clamping

Measuring functions CVMMXN, CMMXU, VMMXU and VNMMXU have no interconnections regarding
any settings or parameters.
Zero clampings are also handled entirely by ZeroDb separately for each function's every output signal.
For example, zero clamping of U12 is handled by UL12ZeroDb in VMMXU, zero clamping of I1 is
handled by IL1ZeroDb in CMMXU, and so on.
Example of CVMMXN operation
Outputs seen on the local HMI under Main menu/Measurements /Monitoring/Servicevalues(P_Q) /
CVMMXN(P_Q):
S
P
Q
PF
ILAG
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Phasor measurement unit RES670
Application manual
The power system quantities provided, depends on the actual hardware, (TRM) and the logic
configuration made in PCM600.
Apparent three-phase power
Active three-phase power
Reactive three-phase power
Power factor
I lagging U
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Section 16
Monitoring
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