Alstom MiCOM P546 - 1.17 Load blinding (load avoidance) (Distance option only); 1.18 Distance elements basic scheme setting (Distance option only)

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-43
OP
1.17 Load blinding (load avoidance) (Distance option only)
Load blinders are provided for both phase and ground fault distance elements, to prevent
misoperation (mal-tripping) for heavy load flow. The purpose is to configure a blinder
envelope which surrounds the expected worst case load limits, and to block tripping for any
impedance measured within the blinded region. Only a fault impedance which is outside of
the load area will be allowed to cause a trip. The blinder characteristics are shown in
Figure 23.
P1232ENa
P1134ENa
Blind
Blind
Blind
Operate
R
Blind
Operate
Load
Radius
Z
X
b
Figure 23 Load blinder characteristics (Distance option only)
In Figure 23:
 Z den
otes the Load/B Impedance
setting. This sets the radius of the underimpedance
circle.
  denotes the Load/B Angle
setting. This sets the angle of the two blinder boundary
lines - the gradient of the rise or fall with respect to the resistive axis.
The MiCOM P54x has a facility to allow the load blinder to be bypassed any time the
measured voltage for the phase in question falls below an undervoltage V< setting. Under
such circumstances, the low voltage could not be explained by normal voltage excursion
tolerances on-load. A fault is definitely present on the phase in question, and it is acceptable
to override the blinder action and allow the distance zones to trip according to the entire
zone shape. The benefit is that the resistive coverage for faults near to the relay location
can be higher.
1.18 Distance elements basic scheme setting (Distance option only)
Config
uration of which zones will trip, and the zone time delays is set in the menu column
GROUP x SCHEME LOGIC (where x is the setting group). Phase and ground elements
may have different time delays if required. Operation of distance zones according to their
set time delays is termed the Basic Scheme, and is shown in Figure 24. The basic scheme
alway
s runs, regardless of any channel-aided acceleration schemes which may be enabled
(see later).