Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.36 Open-Pole OSB Unblock Logic; Figure 5.37 Zero-Setting OOS Blocking Function; Out-Of-Step Logic (Zero Settings)

5.56
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Out-of-Step Logic (Zero Settings)
Out-of-Step Logic (Zero Settings)
Use the zero-setting out-of-step (OOS) blocking function element when the slip
frequency of your system is in the 0.1 to 7 Hz range. (Download the technical
paper “Zero-Setting Power-Swing Blocking Protection” by G. Benmouyal,
Daqing Hou, and Demetrios Tziouvaras from the SEL website for more informa-
tion).
To use the conventional power swing blocking function, set EOOS = Y.
To use the zero-setting power swing blocking function, set EOOS = Y1.
No-Setting OOS Blocking Base Block Diagram
The zero-setting out-of-step blocking function is based on the five functional
blocks shown in Figure 5.37. These blocks are the swing-center voltage slope
detector, the swing signature detector, the reset conditions, the dependable out-
of-step blocking detector, and the three-phase fault detector. Notice that when
either SD (swing-center voltage slope detector) or SSD (swing signature detec-
tor) asserts, the Latch is set, and OSB_I and OSB are also latched.
Figure 5.36 Open-Pole OSB Unblock Logic
I0LFA–IA2LFA
SPO
50QR
50QF
50GR
OSBB
OSBC
OSBA
SPOA
SPOB
SPOC
50GF
–60 to 60
ENABLE
60 to 180
–60 to –180
Figure 5.37 Zero-Setting OOS Blocking Function
OR 1
AND 1
OSB
OSB_I
SD
SSD
RST
DOSB
DTF
OR 2
Latch
Swing Signature
Detector
Reset Conditions
Dependable OSB
Detector
Three-Phase
Fault Detector
S
R
Swing Center Voltage
Slope Detector