4.5.5.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of ROVPTOV can be described by using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 344: Functional module diagram
Level detector
The residual voltage is compared to the set
Start value. If the value exceeds
the set
Start value, the level detector sends an enable signal to the timer. The
residual voltage can be selected with the
Uo signal Sel setting. The options are
"Measured Uo" and "Calculated Uo". If "Measured Uo" is selected, the voltage ratio
for Uo-channel is given in the global setting Configuration > Analog inputs >
Voltage (Uo,VT). If "Calculated Uo" is selected, the voltage ratio is obtained from
phase-voltage channels given in the global setting Configuration > Analog inputs >
Voltage (3U,VT).
Example 1: Uo is measured from the open-delta connected VTs (20/sqrt(3) kV :
100/sqrt(3) V : 100/3 V). In this case, "Measured Uo" is selected. The nominal values
for residual voltage is obtained from the VT ratios entered in Residual voltage Uo:
Configuration > Analog inputs > Voltage (Uo,VT): 11.547 kV:100 V. The residual
voltage start value of 1.0 × Un corresponds to 1.0 × 11.547 kV = 11.547 kV in the
primary.
Example 2: Uo is calculated from the phase quantities. The phase VT-ratio is 20/
sqrt(3) kV : 100/sqrt(3) V. In this case, "Calculated Uo" is selected. The nominal value
for residual voltage is obtained from the VT ratios entered in Residual voltage Uo:
Configuration > Analog inputs > Voltage (3U,VT): 20.000kV : 100V. The residual
voltage start value of 1.0 × Un corresponds to 1.0 × 20.000 kV = 20.000 kV in the
primary.
If "Calculated Uo" is selected, the nominal value of residual voltage is
always phase-to-phase voltage. Thus, the valid maximum setting for
residual voltage
Start value is 0.577 × Un. The calculated Uo requires that
all three phase-to-earth voltages are connected to the protection relay.
Uo cannot be calculated from the phase-to-phase voltages.
Timer
Once activated, the timer activates the
START
output. The time characteristic is
according to DT. When the operation timer has reached the value set by
Operate
delay time, the
OPERATE
output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the
1MRS757644 H
Protection functions
620 series
Technical Manual
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