Schweitzer Engineering Laboratories SEL-421-4 - Page 471

6.135
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
Out-of-Step Logic Application Examples
Out-of-Step Block Time Delay
Set OSBD longer than OSTD by the next timer setting step (0.125-cycle step
size) greater than 0.500 cycle. Thus, the OSBD setting is calculated in
Equation 6.87.
Equation 6.87
OSBD := 1.500. Out-of-Step Block Time Delay (0.500–8000 cycles)
To find the effective slip rate for OOS blocking, solve Equation 6.88 for f
slip
.
Equation 6.88
The relay detects OOS blocking conditions for power swing slip frequencies up
to 5.95 Hz and OOS tripping conditions for power swing slip frequencies from
5.95 Hz to 10.2 Hz (see Equation 6.86). Zone 1 and Zone 2 elements remain
blocked during these OSB and OST conditions. The event is not a swing condi-
tion if the Z
1
impedance locus crosses Zone 7 and Zone 6 before the OSTD and
OSBD timers time out. The relay identifies this event as a fault condition.
Latch Out-of-Step Blocking
Latch out-of-step blocking to maintain the blocking condition throughout the
entire swing cycle.
OSBLTCH := Y. Latch Out-of-Step Blocking (Y, N)
Control Outputs
For local OOS tripping, configure the relay control outputs for tripping and
remote notification of an out-of-step condition. Include Relay Word bit OST in
the direct tripping SEL
OGIC control equation TR. (Add OR OST to the existing
TR equation; the default is shown here.)
TR := Z1P OR Z1G OR M2PT OR Z2GT OR OST. Trip (SELOGIC Equation)
Set a control output for remote notification of the out-of-step tripping condition.
This example uses OUT205. Select a relay control output that is appropriate for
your particular application.
OUT205 := OST. Output OUT205 (SELOGIC Equation)
OSBD OSTD 0.500 cycle timer step++=
0.875 0.500 0.125++=
1.500 cycles=
f
slip
Ang_R6 Ang_R7–f
NOM
•
360
cycle
------------
OSBD•
---------------------------------------------------------------------------=
120.0 66.4–60 Hz•
360
cycle
------------ 1.500 cycle•
--------------------------------------------------------------=
5.5 Hz=