P54x/EN OP/La4 Operation
(OP) 5-38
MiCOM P543, P544, P545 & P546
OP
A reactance line is formed by the phase comparison between an operating signal V/I - Z,
which is the same as that used for the equivalent mho element, and a polarizing signal Iref/I.
Where:
V is the fault voltage
is the fault current (always presented at zero degree)
Z is the zone reach setting, including residual compensation
ref is the negative sequence current for dynamic tilting or phase current for the fixed angle
tilting that includes the initial tilt angle setting (set to -3° as default).
Dynamic tilting:
When the Dynamic tilting is selected by a user, the top line of the ground distance
quadrilateral characteristic will start
tilting from the user settable angle (default angle is -3°)
and tilt further for the angle difference between the fault current and the negative sequence
current so that an overall tilt angle with the reference to fault (phase) current ‘I’ will be:
Tilt angle = ∠Iref/I = setting + ∠(Iph-I2)
Operation occurs when the operating signal lags the polarizing signal.
The default starting (initial) tilt angle of -3° is introduced to reduce the possibility of overreach
caused by any small differences between the negative sequence source impedances, and
general CT/VT angle tolerances.
Negative sequence current is used for ground fault ref since it provides a better estimate of
the current in the fault than either the faulted phase current or zero sequence current. As a
result the reactance line follows the fault resistance impedance and tilts up or down
(depending on the load direction) starting from the set initial tilt angle to avoid underreach or
overreach.
The following additional constraints also exist to ensure that the top line does not tilt too far:-
The Zone 1 reactance (top) line can only stay at set initial tilt angle (-3° default)
compared to the resistive axis, or can tilt down by ∠(Iph-I2) . The top line may never tilt
up from set tilting angle, to ensure that Zone 1 does not overreach. This maintains
grading/selectivity with downstream protection.
The Zone 2 reactance (top) line can only ever stay at set tilt angle (-3° default) compared
to the resistive axis, or can tilt up by ∠(Iph-I2). The top line may never tilt down, to
ensure that Zone 2 does not underreach. This is particularly important when Zone 2 is
used to key channel-aided distance schemes.
The maximum permissible tilt is +/- 45° either side of the set initial tilt angle (-3° default)
When one circuit breaker pole is open, during a single pole reclose sequence, the polarizing
signal is replaced by the fault current with a -7° phase shift, allowing the protection of the
remaining phases, even though the negative sequence current is not available. The
additional phase shift is provided to reduce the possibility of overreach caused by the faulted
phase as the reference.
Predetermined (fixed angle) tilting:
For the phase quadrilateral characteristics and ground quad characteristics in case when
Dynamic tilting is disabled, the fix angle setting settable by a user applies. Each zone has an
independent tilt angle setting. The total tilting angle with the reference to fault current ‘I’ is
equal to the set angle:
Tilt angle = ∠Iref/I = setting
Note: A minus angle is used to set a downwards tilt gradient, and a positive
angle to tilt upwards.
Operation occurs when the operating signal lags the polarizing signal. The setting range is
+/- 30°.
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