Figure 4.9.3-1 Voltage Detector Operation - Siemens Argus 7SR21 Technical Manual

7SR210 & 7SR220 Description of Operation
Voltage detectors
Voltage detectors determine the status of the line or bus. If the voltages on either the line or bus are below a set
threshold level they can be considered to be 'dead'. If the voltages are within a setting around the nominal voltage
they are classed as 'live'. Independent voltage detectors are provided for both line and bus.
If a voltage is in the dead band range then it will be classed as dead until it has reached the live band area.
Similarly, if a voltage is live, it continues to be live until it has reached the dead band area. This effectively allows
for variable amounts of hysteresis to be set. Figure 4.9.3-1 illustrates the voltage detector operation.
Note: the area between the dead and live zones is not indeterminate. When any voltage is applied to the relay it
will ramp up the software RMS algorithm and always pass through the dead zone first.
A wide range is provided for live and dead voltage detector levels but the live and dead zones must not overlap.
Figure 4.9.3-1 Voltage Detector Operation
Under-voltage detectors
The under-voltage detectors, if enabled, can block a close output command if either the line voltage is below the
25 Line Undervolts setting value or the bus voltage is below the 25 Bus Undervolts setting value. Both line and
bus have their own independent settings and are applied to the single-phase voltage inputs.
Differential voltage detectors
The differential voltage detector, if enabled, can block a close output command if the difference between the line
and bus voltages is greater than the differential voltage setting value.
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