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To adapt the fault direction determination to possible fault direction change during the
fault, for example, during manual fault location process, a cyclic accumulation of sum
admittance phasors is conducted. The duration of this directional evaluation cycle is 1.2 ·
Reset delay time
(minimum of 600 ms). If the fault direction based on the cyclic phasor
accumulation is opposite to the function direction output for
Reset delay time
or 500 ms
(minimum of 500 ms), the function is reset and fault direction calculation of 67YN is
restarted.
In case the ground-fault protection is alarming, the 67YN includes also a
RESET
input,
which can be utilized to externally re-trigger the fault direction determination, if re-
evaluation of fault direction during a persistent ground fault is required. It is also
recommended to connect the pickup signal of non-directional ground-fault protection
(51N, 51G, 50N, 50G, 50N-3, 50G-3), set to trip in case of a cross-country fault, to
RESET
input of 67YN to reset phasor accumulation during a cross-country fault. 67YN is then
able to adapt to possible fault direction change more rapidly, if single phase ground fault
still persists in the system after the other faulty feeder has been tripped (cross-country fault
has been transformed back to a single phase ground fault).
The direction of the 67YN function is supervised by a settable current magnitude
threshold. The trip current used in the magnitude supervision is measured with a special
filtering method, which provides very stable residual current estimate regardless of the
fault type. This stabilized current estimate is the result from fundamental frequency
admittance calculation utilizing the CPS technique. The stabilized current value is
obtained (after conversion) from the corresponding admittance value by multiplying it
with the system nominal phase-to-ground voltage value, which is entered as a base value
for the residual voltage (V
baseres
). The equations for calculating the stabilized values of the
fundamental frequency admittance and the corresponding current are given below.
Y
I
V
Y
j
Y
G
o stab
CPS
CPS
o stab
o stab
ost
1
0
1
0
1
1
1
3
=
⋅
−
=
+ ⋅
=
Re
Im
a
ab
ostab
j B
1
1
+ ⋅
GUID-66B0BAEF-BDA1-40CF-B5A0-71B7D0284C03 V1 EN
(Equation 63)
Y
o stab
1
The stabilized fundamental frequency admittance estimate, which is result from fundamental
frequency admittance calculation utilizing the Cumulative Phasor Summing (CPS) technique.
I
CPS
0
1
The fundamental frequency zero-sequence current phasor calculated utilizing the Cumulative
Phasor Summing (CPS) technique.
V
CPS
0
1
The fundamental frequency zero-sequence voltage phasor calculated utilizing the Cumulative
Phasor Summing (CPS) technique.
G
o stab
1
The real-part of stabilized fundamental frequency conductance estimate.
B
o stab
1
The imaginary part of stabilized fundamental frequency susceptance estimate.
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
445
Technical Manual
Содержание Relion 615 series
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