4.99
Date Code 20100129
Instruction Manual
SEL-751A Relay
Protection and Logic Functions
Arc-Flash Protection
having the overcurrent element (50PAF) supervise the light element (TOLn) in
the output logic (OUTxxx := 50PAF AND TOLn). This approach offers
fastest tripping times, but is less secure (can be tripped with the light input
only).
Output Logic
Programming
As stated earlier, arc-flash protection involves detecting an overcurrent as well
as light (arc). Location of the light sensors and source(s) of the arc energy
must also be considered in developing the trip output logic. If the relay detects
both signals simultaneously, it is desirable to trip the “source breaker(s).”
The Relay Word bits for arc-flash protection (see
and
are:
50PAF, 50NAF, TOL1, TOL2, TOL3, and TOL4
As described earlier, you select two output contacts for high-speed processing
by setting AOUTSLOT appropriately. The high-speed contact should be used
for arc-flash tripping instead of the default OUT103 shown in
. Also
to ensure all the advantages of the trip logic (trip seal-in, event report trigger,
etc.) the arc-flash trip should be included in the trip equation TR (see
for detail).
NOTE:
The high-speed outputs
selected by AOUTSLOT setting being
Form A, cannot be used in fail safe
mode (see Fig 2.later) and should be
disabled (set OUTxxxFS := N).
To get additional speed select the fast hybrid output option card (4DI/4DO).
This card contains trip duty rated solid state output contacts, which will
operate within 50 µs (up to 8 ms faster than the standard electromechanical
outputs).
EXAMPLE 4.23
Output Logic Programming Example 1:
SEL-751A applied at the source breaker.
Assume light sensors LS1, LS2, and LS3 are located downstream of
the source breaker and output contacts in slot 3 are selected for high-
speed processing (AOUTSLOT := 301_2).
Set:
OUT301FS :=
N
OUT301 :=
(50PAF OR 50NAF) AND (TOL1 OR TOL2 OR TOL3) OR TRIP
TR :=
ORED50T OR ORED51T OR
…
OR (50PAF OR 50NAF) AND (TOL1 OR
TOL2 OR TOL3
)
EXAMPLE 4.24
Output Logic Programming Example 2:
SEL-751A applied at the radial feeder breaker.
Assume light sensors LS1 and LS2 are located downstream, LS3 is
located upstream of the feeder breaker, and output contacts in slot 3
are selected for the high speed processing (AOUTSLOT := 301_2).
Set:
OUT301FS :=
N,
OUT302FS :=
N
OUT301 :=
(50PAF OR 50NAF) AND (TOL1 OR TOL2) OR TRIP
OUT302 :=
TOL3
TR :=
ORED50T OR ORED51T OR
…
OR (50PAF OR 50NAF) AND (TOL1 OR
TOL2)
Use the OUT302 contact to trip upstream breaker. Note that OUT302
does not include overcurrent element supervision. When desired, this
supervision should be added by upstream relay(s). For instance, you
can do the following:
➤
Connect OUT302 of breaker 2 relay to drive IN302 of the
breaker 1 relay
➤
Add IN302 to the OR string of TOLn in both OUT301 and TR
equations of breaker 1 relay.
You can use M
IRRORED
B
ITS
instead of IN302 for faster operation if
desired.
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