5-30 Trip and Target Logic Date Code 20001006
SEL-351 Instruction Manual
Additional Target LED Information
TRIP Target LED
The TRIP target LED illuminates at the rising edge of trip (the new assertion of the TRIP Relay
Word bit).
The TRIP target LED is especially helpful in providing front-panel indication for tripping that does
not involve overcurrent or frequency elements. If the trip is not an overcurrent or frequency
element generated trip, none of the target LEDs numbered 3 through 13 in Table 5.1 illuminate, but
the TRIP target LED still illuminates. Thus, tripping via the front-panel local control (local bits),
serial port (remote bits or OPEN command), or voltage elements is indicated only by the
illumination of the TRIP target LED.
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 3
cycles of fault inception, the INST target illuminates.
SELOGIC Control Equation setting FAULT also controls max./min. metering. If FAULT is
asserted, maximum/minimum metering is blocked (see Maximum/Minimum Metering in Section
8: Breaker Monitor, Metering, and Load Profile Functions). Fault current values are not to be
accrued as maximum current values in maximum/minimum metering.
COMM Target LED
The COMM target LED illuminates at the rising edge of trip if the trip is the result of SELOGIC
Control Equation setting TRCOMM and associated communications-assisted trip logic, Relay
Word bit ECTT, or SELOGIC Control Equation setting DTT (see Figure 5.1, top half of figure).
Another Application for the COMM Target LED
If none of the traditional communications-assisted trip logic is used (i.e., SELOGIC Control
Equation setting TRCOMM is not used; see Figure 5.4 and accompanying text), consideration can
be given to using the COMM target LED to indicate tripping via remote communications
channels (e.g., via serial port commands or SCADA asserting optoisolated inputs). Use SELOGIC
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 in Section 10: Serial
Port Communications and Commands) are used to trip via the serial port and they should
illuminate the COMM target LED, set them in SELOGIC Control Equation setting DTT:
DTT = … + OC + RB1
Courtesy of NationalSwitchgear.com
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