BLK_EF
OPERATE
Io
Uo
BLOCK
START
Timer 2
t
Timer 1
Transient
detector
Fault
indication
logic
Level
detector
Blocking
logic
Figure 159: Functional module diagram
Level detector
The residual voltage can be selected from 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 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 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 phase quantities. The phase VT-ratio is 20/sqrt(3)
kV : 100/sqrt(3) V. In this case, "Calculated Uo" is selected. The nominal values for
residual current and residual voltage are obtained from VT ratios entered in Residual
voltage Uo: Configuration > Analog inputs > Voltage (3U,VT): 20.000 kV : 100 V. 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 residual voltage nominal value is always
phase-to-phase voltage. Thus, the valid maximum setting for residual
voltage start value is 0.577 × Un. 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.
Transient detector
The Transient detector module is used for detecting transients in the residual
current and residual voltage signals.
The transient detection is supervised with a settable current threshold. With
a special filtering technique, the setting
Min operate current is based on the
fundamental frequency current. This setting should be set based on the value of
Protection functions
1MRS758755 C
334
REC615 & RER615
Technical Manual
