Schweitzer Engineering Laboratories SEL-751 - Table; Figure 4.56 HIF Detection Block Diagram

4.83
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
Figure 4.56 HIF Detection Block Diagram
HIF Detection Settings
Table 4.28 lists the relay settings corresponding to high-impedance fault
detection. High-impedance fault detection is enabled by group setting
EHIF := Y or T. When EHIF is set to Y, the detection algorithm begins calcu-
lating a running average of the applicable algorithm quantity to provide a sta-
ble prefault reference. This initial tuning asserts Relay Word bits ITUNE_x
(where x = A, B, C). This process takes 24 hours but is interrupted by a change
in the EHIF setting value, a change in the FNOM setting value, a loss of load
current, or a relay trip condition.
Once interrupted, the initial tuning restarts the next time the relay detects load
current. If necessary, it can be restarted with the INI HIF command or by
asserting the programmable SEL
OGIC control equation HIFITUNE. See INI
HIF Command in Section 7: Communications for more information on the
INI HIF command. After the initial tuning process, the relay retains the
learned value for four hours. If a line is de-energized for more than four hours,
Note: A-phase logic is shown above; B-phase and C-phase are similar.
(d) Detection Signal Generation SDI Non-Harmonic
SDIA
k
DAI
k-63
DIA
k-1
DIA
k
M1
M2
IAL
k
IAL at 32 s/cyc
(freq. tracked)
1-cyc memory
{IA
k-1
... IA
k-32
}
runs every 2-cycle
IA
k-32
2-cyc memory
{DIA
k-1
... DIA
k-63
}
(c) Block Diagram of HIF Detection Non-Harmonic
SDIA
IA
HIF2_A
HIA2_A
Adaptive Tuning
Blocking Conditions
Decision Logic 2Trending and Memory
IIR Limiting
Averager 2
Detection Signal
Generation 2
(b) Detection Signal Generation ISM Odd-Harmonic
|IAs
k-1
|
ISMA
k
runs every 2-cyc
IAs
k
|IAs
k
|
IA
k
, ... IA
k-SRATE+1
1-Cycle
FIR Filter
Near 2-cyc memory
{|IAs
k-1
|...|IAs
k-2 •SRATE + 1
|}
(a) Block Diagram of HIF Detection Odd-Harmonic
IA
HIF1_A
HIA1_A
Detection Signal
Generation 1
FIR Smoothing
IIR Limiting
Averager 1
Statistics
Decision Logic 1
Difference
ISMA
NOTE: It is recommended to use
EHIF := Y for field tests and follow the
initial tuning process.