8-52 BE1-951 Application 9328900990 Rev L
Referring to Figure 8-18, if sensing voltage is above the inhibit setting of the under frequency elements
81T and 181T and system frequency is below the 81T and 181T setting, VO6, UF_TRIP goes high. This
initiates the auto reclose sequence through VO8, RI and forces VO13 (UF_LO) high, closing and sealing
the inputs to VO1 and VO3 through AND gate VO14 (LATCH). This allows the contacts of Output 3 and
Output 4 to transition and remain in that state, simulating "a" and "b" contacts of an electrical reset lockout
relay (86). The VO14 seal also removes the block input from the 281T and 381T over frequency elements
and, either drives the 79 element to lockout (manual close) or puts a "wait" on 79 (auto close). The
associated breaker will be tripped by Output 1 and the close circuit is disabled by Output 3.
Figure 8-18. Underfrequency Load Shed, Circuit Level Application, Manual or Auto Close from SCADA or
Local Restore
When the load condition that initiated the event has subsided, the system operator/dispatcher will initiate
a remote restoration procedure. A "restoration permissive" from the BE1-951 verifies that the following
conditions are met prior to allowing closure of the breaker:
• Under frequency trip, 81T and 181T are no longer present.
• System Frequency and Voltage above the predetermined restore level (281T and 381T).
• The breaker is open.
• The VO14 latch circuit is high.
With VO7, PROT_RES high and the above conditions met, closure of the SCADA Restore contact forces
VO10, REST_PER high, breaking the VO13/VO14 seal and resetting Output 1 and Output 3 contacts. If
automatic reclosing is used, the "WAIT" input is removed and the reclosing element (79) closes the
breaker after a predetermined time delay. If manual reclosing is used, the "DTL/BLK" input is removed
and the breaker is ready to close SCADA or local close.
As with the Bus Level Application, an optional "auto target reset circuit", can be initiated, automatically
resetting the BE1-951 targets and Trip LED and eliminating the need for further operator input. A one-
shot, non-retriggerable timer (62), initiated by VO10, REST_PER is used to automatically reset the BE1-
951 targets and Trip LED via "logic" input to the Target Reset Logic (see Figure 6-4). Fault and Event
records detailing the operation are available from the relay.
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