ABB RER615 - Page 343

4.2.4.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of EFPADM can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
OPERATE
Neutral
admittance
calculation
BLOCK
START
Io
Uo
RELEASE
t
Timer
Operation
characteristics
Blocking
logic
Figure 165: Functional module diagram
Neutral admittance calculation
The residual current can be selected from the Io signal Sel setting. The setting
options are "Measured Io" and "Calculated Io". If "Measured Io" is selected, the
current ratio for Io-channel is given in Configuration> Analog inputs> Current
(Io,CT). If "Calculated Io" is selected, the current ratio is obtained from phase-
current channels given in Configuration> Analog inputs> Current (3I,CT).
Respectively, the residual voltage can be selected from the Uo signal Sel setting.
The setting options are "Measured Uo" and "Calculated Uo". If "Measured Uo"
is selected, the voltage ratio for Uo-channel is given in Configuration> Analog
inputs> Voltage (Uo,VT). If "Calculated Uo" is selected, the voltage ratio is obtained
from phase-voltage channels given in 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 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 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.
In case, 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. 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.
When the residual voltage exceeds the set threshold Voltage start value , an earth
fault is detected and the neutral admittance calculation is released.
1MRS758755 C
Protection functions
REC615 & RER615
Technical Manual
343