8-54
Application
BE1-951
Figure 8-18. Underfrequency Load Shed, Circuit Level Application, Manual or Auto Close
from SCADA or Local Restore.
381T elements. Also, VO4 will go low, opening Output 4 contact, removing the 86UF Restore Permissive.
The last 86UF to reset can initiate an optional “auto target reset circuit”, thus eliminating the need for further
operator input. A one-shot, non-retriggerable timer (62), initiated by the last lockout to reset (Input 1), is
used to automatically reset the 951 targets and Trip LED via “logic” input to the
Target Reset Logic, see
Figure 6-4, Section 6). Fault and Event records detailing the operation are available from the relay.
Circuit Level Application—Manual and Auto Reclosing:
The following logic was designed to work with the preprogrammed OC-W-79 Logic Scheme described in ,
Section 8,
Application.
For the Bus Application, load restoration was accomplished by resetting the lockout relays (86UFs) and
allowing the circuit recloseing relays to close the breaker and restore load. Using the Circuit Level
Application, restoration can be accomplished by an automatic or manual closure of the breaker. Both
methods are described in the following paragraphs.
Referring to Figure 8-18, if sensing voltage is above the inhibit setting of the under frequency elements 81
and 181T, and system frequency is below the 81 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 281 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.
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 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 (281 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 reseting output 1 and Output 3 contacts. If
Содержание BE1-951
Страница 157: ...BESTlogic Programmable Logic BE1 951 7 2 Figure 7 1 BESTlogic Function Blocks Courtesy of NationalSwitchgear com...
Страница 238: ...BE1 951 Human Machine Interface 10 5 Figure 10 5 Metering Menu Branch Structure Courtesy of NationalSwitchgear com...
Страница 239: ...10 6 Human Machine Interface BE1 951 Figure 10 6 Reports Menu Branch Structure Courtesy of NationalSwitchgear com...
Страница 270: ...12 2 Installation BE1 951 Figure 12 1 BE1 951 S1 Case Dimensions Courtesy of NationalSwitchgear com...
Страница 274: ...12 6 Installation BE1 951 Figure 12 5 BE1 951 H1 Case Dimensions Courtesy of NationalSwitchgear com...
Страница 283: ...BE1 951 Installation 12 15 Figure 12 16 Typical AC Connections Courtesy of NationalSwitchgear com...
Страница 394: ...A 18 Appendix BE1 951 Figure A 14 Time Characteristic Curve B Very Inverse 99 1376 Courtesy of NationalSwitchgear com...
Страница 396: ...A 20 Appendix BE1 951 Figure A 16 Time Characteristic Curve G Long Inverse 99 1622 Courtesy of NationalSwitchgear com...
Страница 397: ...BE1 951 Appendix A 21 Figure A 17 46 Time Characteristic Curve Courtesy of NationalSwitchgear com...