• Zero-point clamping
• Deadband supervision
• Limit value supervision
In the three-phase voltage measurement function VMMXU the
supervision functions are based on the phase-to-phase voltages.
However, the phase-to-earth voltage values are also reported with
the phase-to-phase voltages.
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 531: Zero-point clamping limits
Function
Zero-clamping limit
Three-phase current measurement (CMMXU) 1% of nominal (In)
Three-phase voltage measurement (VMMXU) 1% of nominal (Un)
Residual current measurement (RESCMMXU) 1% of nominal (In)
Residual voltage measurement (RESVMMXU) 1% of nominal (Un)
Phase sequence current measurement (CSMSQI) 1% of the nominal (In)
Phase sequence voltage measurement
(VSMSQI)
1% of the nominal (Un)
Three-phase power and energy measurement
(PEMMXU)
1.5% of the nominal (Sn)
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.
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 (50/60 Hz) and also the
quality information of the data set accordingly.
1YHT530004D05 D Section 8
Measurement functions
615 series 627
Technical Manual
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