ABB RELION SMU615 Technical Manual page 184

Measurement functions
Zero-point clamping
A measured value under the zero-point clamping limit is forced to zero. This allows
the noise in the input signal to be ignored. The active clamping function forces
both the actual measurement value and the angle value of the measured signal to
zero. In the three-phase or sequence measuring functions, each phase or sequence
component has a separate zero-point clamping function. The zero-value detection
operates so that once the measured value exceeds or falls below the value of the
zero-clamping limit, new values are reported.
Table 203: Zero-point clamping limits
Function
Three-phase current measurement (CMMXU) 1% of nominal (In)
Three-phase voltage measurement (VMMXU) 1% of nominal (Un)
Residual current measurement (RESCMMXU)
Phase sequence current measurement
(CSMSQI)
Phase sequence voltage measurement
(VSMSQI)
Three-phase power and energy measurement
(PEMMXU)
Limit value supervision
The limit value supervision function indicates whether the measured value of
X_INST exceeds or falls below the set limits. The measured value has the
corresponding range information X_RANGE and has a value in the range of 0 to 4:
• 0: "normal"
• 1: "high"
• 2: "low"
• 3: "high-high"
• 4: "low-low"
The range information changes and the new values are reported.
184
When the frequency measurement function FMMXU is unable to measure
the network frequency in the undervoltage situation, the measured
values are set to the nominal and also the quality information of the
data set accordingly. The undervoltage limit is fixed to 10 percent of the
nominal for the frequency measurement.
Zero-clamping limit
1% of nominal (In)
1% of the nominal (In)
1% of the nominal (Un)
1.5% of the nominal (Sn)
1MRS758407 C
SMU615
Technical Manual