
R
X
Load blinder forward area
(Load-out region or Load exporting)
Load blinder reverse area
(Load-in region or Load importing)
Max impedance angle
Min impedance angle
Min impedance angle
Max impedance angle
Nominal impedance
circle
Resistive
reach Fw
Resistive
reach Rv
Load blinder reverse area
(Load-in region or Load importing)
Load blinder forward area
(Load-out region or Load exporting)
Figure 736: Operating sectors for load blinder
The blinder directional operation can be selected with the
Directional mode setting.
The alternatives are "Non-directional", "Forward" and "Reverse" operation.
Forward operation is allowed if
Directional mode is set to “Forward”. If the resistive
part value of positive sequence impedance is higher than
Resistive reach Fw and
the angle of positive sequence impedance stays in the range limited with the
Max
impedance angle and Min impedance angle on forward area, the function output
LB_FORWARD
is activated.
Reverse operation is allowed if
Directional mode is set to “Reverse”. If the resistive
part value of positive sequence impedance exceeds the limitation of
Resistive reach
Rv and the angle of positive sequence impedance stays in the range limited with the
Max impedance angle and Min impedance angle on reverse area, the function output
LB_REVERSE
is activated.
In case
Directional mode is set to “Non-directional”, operation is allowed both
directions according to conditions described above.
Activation of the
BLOCK
input deactivates the function outputs.
5.16.6
Application
Load blinder or load encroachment, function LBRDOB is used to block the
directional overcurrent protection aiming at avoiding incorrect trip in case of heavy
loading condition in network. In general, the active power increases to the level
leading to a high power factor, the network turns into heavy load status, and there
exists risk of incorrect trip for the directional overcurrent protection because of
high level of load current.
The suitability of
Resistive reach Fw and Resistive reach Rv settings will influence
the activation of load blinder function. If
Resistive reach Fw and Resistive reach Rv
are set beyond the network minimal resistive load, the function will not be activated
in the case that the load impedance approaches the network minimal impedance
load. Hence, the absolute values of
Resistive reach Fw and Resistive reach Rv should
be set less than that of the minimal resistive load.
1MRS759142 F
Protection related functions
REX640
Technical Manual
1297