5.11
Date Code 20080213 Instruction Manual SEL-351A Relay
Trip and Target Logic
Front-Panel Target LEDS
INST Target LED
The INST target LED illuminates at the rising edge of trip if SELOGIC control
equation setting FAULT has been asserted for less than 3 cycles. FAULT is
usually set with time-overcurrent element pickups (e.g., FAULT = 51P + 51G)
to detect fault inception. If tripping occurs within three cycles of fault
inception, the INST target illuminates.
SEL
OGIC control equation setting FAULT also controls other relay functions.
See subsection SEL
OGIC Control Equation Setting FAULT on page 5.13.
COMM Target LED
The COMM target LED illuminates at the rising edge of trip if the trip is the
result of SEL
OGIC control equation setting DTT (see top of Figure 5.1).
Another Application for the COMM Target LED
The Direct Transfer Trip (DTT) SELOGIC setting can also be used to indicate
tripping via remote communications channels (e.g., via serial port commands
or SCADA asserting optoisolated inputs). Use SEL
OGIC control equation
setting DTT (Direct Transfer Trip) to accomplish this (see Figure 5.1).
For example, if the OPEN command or remote bit RB1 (see CON Command
(Control Remote Bit) on page 10.36) are used to trip via the serial port and
they should illuminate the COMM target LED, set them in SEL
OGIC control
equation setting DTT:
DTT = … + OC + RB1
Additionally, if SCADA asserts optoisolated input IN104 to trip and it should
illuminate the COMM target LED, set it in SEL
OGIC control equation setting
DTT also:
DTT = … + IN104 + …
Relay Word bits set in SEL
OGIC control equation setting DTT do not have to
be set in SEL
OGIC control equation setting TR because both settings directly
assert the TRIP Relay Word bit. The only difference between settings DTT
and TR is that setting DTT causes the COMM target LED to illuminate.
Many other variations of the above DTT settings examples are possible.
SOTF Target LED
The SOTF target LED illuminates at the rising edge of the TRIP Relay Word bit
if the trip is the result of the SEL
OGIC control equation setting TRSOTF and
associated switch-onto-fault trip logic (see Figure 5.3).
50 Target LED
The 50 target LED illuminates at the rising edge of trip if an instantaneous or
definite-time overcurrent element causes the trip.
51 Target LED
The 51 target LED illuminates at the rising edge of trip if a time-overcurrent
element (51PT, 51AT, 51BT, 51CT, 51NT, 51GT, 51G2T, or 51QT) causes the
trip.
Courtesy of NationalSwitchgear.com
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