The characteristic
Tilt angle should reflect the measurement errors, that
is, the larger the measurement errors, the larger the
Tilt angle setting
should be. Typical setting value of 5 degrees is recommended.
The detected fault direction is available in the Monitored data view as parameter
DIRECTION.
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 MFADPSDE is restarted.
In case the earth-fault protection is alarming, the MFADPSDE 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 earth fault is
required. It is also recommended to connect the start signal of non-directional
earth-fault protection (EFxPTOC), set to operate in case of a cross-country fault,
to
RESET
input of MFADPSDE to reset phasor accumulation during a cross-country
fault. MFADPSDE is then able to adapt to possible fault direction change more
rapidly, if single phase earth 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 earth fault).
The direction of the MFADPSDE function is supervised by a settable current
magnitude threshold. The operate 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-earth voltage value, which is entered as a base value for the residual voltage
(U
baseres
). The equations for calculating the stabilized values of the fundamental
frequency admittance and the corresponding current are given below.
Y
I
U
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
+ ⋅
(Equation 55)
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.
U
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.
1MRS757644 H
Protection functions
620 series
Technical Manual
487
