GE MiCOM P40 Agile, Technical Manual, Page: 174 / 962

 
A C C B B A BIAS
I I I I I I I
   
, , max Bias current
N
eu
tr
al
c
ur
re
n
t
C B A N
I I I I
  
% 10

K
V02777
Figure 61: Biased Neutral Current Detector Characteristic
The neutral current detector uses the maximum of the three phase current differences as a biasing value. The
slope of the characteristic is fixed at 10%.
Biasing the neutral current detector assures that the detector is sensitive enough to operate for any single-phase
fault, without the risk of picking up on neutral spill current during phase-to-phase faults. The neutral spill current
might arise from mismatched current transformers or current transformer saturation. The biasing also ensures
that the earth fault distance elements are generally disabled for double-phase-to-earth faults with high resistance
in the neutral. Such faults can occur in resistively earthed systems, or in solidly earthed systems due to high arc
resistance. Given that these conditions are very similar to pure phase-to-phase faults, the earth fault distance
elements can exhibit high measuring errors which the use of the neutral current detector overcomes.
4.6 DISTANCE ELEMENT ZONE SETTINGS
The settings for the Distance protection are contained in the DISTANCE SETUP and DIST. ELEMENTS columns of the
relevant settings group.
The Distance protection has a Setting Mode which is set to
Simple
by default. We recommend the default for
most applications.. Instead of entering distance zone impedance reaches in ohms, zone settings are simply
entered in terms of percentage of the protected line data specified with the Line Impedance setting in the LINE
PARAMETERS column. The setting assumes that the residual compensation factor is equal for all zones. The
protection calculates the required reach settings from the percentage settings. The calculated zone reaches are
available for viewing but you cannot change a value.
An ‘Advanced’ Setting Mode allows individual distance ohmic reaches and residual compensation factors to be
entered for each zone. When ‘Advanced’ mode is selected, all ‘percentage’ settings that are associated to ‘Simple’
setting mode in the DISTANCE SETUP column will be hidden and the Distance zone settings need to be entered for
each zone in the DIST. ELEMENTS column.
If you use the ‘Simple’ Settings Mode, the DISTANCE ELEMENTS column contains a list of what settings have been
automatically calculated and applied. This list is useful as a reference for commissioning and periodic injection
testing. If you use the ‘Advanced’ Setting Mode, however, you must enter all settings for each zone.
Note:
Distance zones are directionalized by a Delta Directional decision. The characteristic angle for this decision is set with the
Delta Directional configuration, in the DISTANCE SETUP column. The default setting is 60°.
4.6.1 DIRECTIONALIZING THE DISTANCE ELEMENTS
By default a Delta technique is used for directionalizing the Distance protection. It acts on step-changes (Deltas) of
current and voltage to determine whether potential fault conditions are in the forward or reverse direction. The
Delta voltage and current thresholds used in the Distance Directional decision are fixed for optimum performance.
The Directional characteristic angle, (also known as the relay characteristic angle – RCA) is set to 60° by default,
but you can change this to suit your application using the Dir. Char Angle setting in the DISTANCE SETUP column.
Chapter 7 - Distance Protection P446SV
142 P446SV-TM-EN-1