Alstom MiCOM P546 - 1.15.3 Distance zone sensitivities (Distance option only)

Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546 (OP) 5-41
OP
1.15.3 Distance zone sensitivities (Distance option only)
When the Simple setting mode is selected, the minimum current sensitivity still applies, but
the value is automatically calculated and applied based on the data entered into the simple
settings fields. The criteria used to calculate the setting value is required to satisfy a
minimum value of current flowing in the faulted loop and a requirement on the Zone reach
point voltage. For Zones 3, P, and 4, the requirements are that the minimum current must
be greater than 5% of rated current, and that the minimum voltage at the Zone reach point is
0.25 V. The current equating to the reach point criteria can be expressed as 0.25/Zone
reach, and the sensitivity can be expressed as:-
Sensitivity (Z3, ZP, Z4) = max (5%In, (0.25/Zone reach))
For Zones 1 and 2, the sensitivity is further qualified to ensure that they are set less sensitive
that the reverse Zone 4. This is designed to ensure stability of the relay where applied with
either an overreaching, or a blocking scheme. For Zones 1 and 2, the same criteria as for
Zones 3, P, and 4 are applied, but in addition a minimum sensitivity criterion dependent upon
the Zone 4 sensitivity is applied : the sensitivity must also exceed 1.5 x Zone 4 sensitivity.
The sensitivity can be expressed as:-
Sensitivity (Z1, Z2) = max (5%In, (0.25/Zone reach), (1.5 x Zone 4 sensitivity))
Or
Sensitivity (Z1, Z2) = max (5%In, (0.25/Zone reach), (1.5 x (0.25/Zone 4 reach)))
Note 1: The dependency on the Zone 4 element always applies, even if Zone
4 is disabled.
Note 2: The default reach setting for Zones 1, 2, and 4 are 80%, 120%, and
150% respectively and for these settings, the “Zone dependent” terms
can be reduced to:-
0.25/Zone 1 reach = 0.25/(0.8 x line impedance)
0.25/Zone 2 reach = 0.25/(1.2 x line impedance)
1.5 x (0.25/Zone 4 reach) = 0.25/line impedance
In such cases, for Zone 1, the dominant Zone reach term will be that of Zone 1 and the
equation can be reduced to:-
Sensitivity (Z1) = max (5%In, (0.25/(0.8 x line impedance)))
And it can be shown that for lines with an impedance less than 6.25 Ω the Zone 1 reach term
will dominate and the sensitivity will be greater than 5% In. Above this line impedance the
sensitivity will be 5% In.
Similarly, for Zone 2, the dominant Zone reach term will be that of Zone 4 and the equation
can be reduced to:-
Sensitivity (Z2) = max (5%In, (0.25/line impedance))
And it can be seen that for lines with an impedance less than 5 Ω the Zone reach term will
dominate and the sensitivity will be greater than 5% In. Above this line impedance the
sensitivity will be 5% In.
In Advanced mode the same restrictions as minimum sensitivity should be applied to ensure
distance element accuracy.