Sel 411L - Figure 3.37 Adaptive Disturbance Detection Algorithm; Table 3.22 Adaptive Threshold Limits in the Adaptive Disturbance Detection Algorithm; Table 3.23 External Fault Detection Relay Word Bits

P.3.64
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
Second, the algorithm uses a slow infinite impulse response (IIR) filter to
average the standing values in the DX signal to obtain a representation of
normal DX values. The algorithm clamps input values to the filter at certain
minimum (MIN) and maximum (MAX) values to better control the filter
according to its intended application in the scheme. Tabl e 3.22 lists the MIN
and MAX levels of the effective threshold for different types of input signals, IN.
Third, the output of the adaptive disturbance detection algorithm, OUT, asserts
if the present value of the magnitude in the phasor change, DX, is greater than
kTH times the standing value in the DX signal (kTH is a factory constant of 3).
For example, assume that the DX value from the local positive-sequence
current in the W current terminal oscillates at about one percent of CT
nominal. This means that the effective threshold the IIR filter developed for
the I1 comparator in the W terminal is 3 • 0.01 • CT nominal. If the positive-
sequence current changes by more than 0.03 • CT nominal, the local
disturbance detector will assert. The 0.03 • CT nominal change may result
from an increase or decrease of three percent of nominal in the magnitude of
the positive-sequence current. It may also result from an angular shift. For
example, assume a near full rating load of 0.8 • CT nominal load. At this
signal level, an angular shift of 1.1 degrees causes a 0.03 • CT nominal phasor
change and triggers the disturbance detector. At 0.2 • CT nominal load, for
example, an angular shift of 4.3 degrees will cause the DX to change by
0.03 • CT nominal and trigger the disturbance.
Figure 3.37 Adaptive Disturbance Detection Algorithm
Table 3.23 lists the disturbance detector logic Relay Word bits. You can use
these bits in custom SEL
OGIC control equations.
Σ
–
-
+
IN
1-cycle
buffer
mag
DX
MAX
MIN
IIR Filter
kTH
TH
OUT
Table 3.22 Adaptive Threshold Limits in the Adaptive Disturbance Detection
Algorithm
Input Phasor MIN TH MAX TH
I1 (positive-sequence, local current) 0.03 • CT
NOM
/kTH 0.15 • CT
NOM
/kTH
I0 (zero-sequence, local current) 0.03 • CT
NOM
/kTH 0.15 • CT
NOM
/kTH
V1 (positive-sequence, local voltage) 0.03 • PT
NOM
/kTH 0.10 • PT
NOM
/kTH
V2 (negative-sequence, local voltage) 0.03 • PT
NOM
/kTH 0.10 • PT
NOM
/kTH
V0 (zero-sequence, local voltage) 0.03 • PT
NOM
/kTH 0.10 • PT
NOM
/kTH
I1 (positive-sequence, remote current) 0.03 pu of 87L/kTH 0.15 pu of 87L/kTH
IG (3I0, remote current) 0.01 pu of 87L/kTH 0.30 pu of 87L/kTH
IQ (3I2, remote current) 0.01 pu of 87L/kTH 0.30 pu of 87L/kTH
Table 3.23 External Fault Detection Relay Word Bits
Name Description
87DD Disturbance detected in local 87L currents or 87LINEV voltages, and
remote 87L currents
87DDL Disturbance detected in local 87L currents or 87LINEV voltages
87DDR Disturbance detected in remote 87L currents