8-8
Application
BE1-951
SL-VO1=VO11
SL-VO2=50TPT
SL-VO3=51PT
SL-VO4=50TNT+50TQT
SL-VO5=51NT+51QT
SL-VO6=0
SL-VO7=0
SL-VO8=0
SL-VO9=0
SL-VO10=0
SL-VO11=50TPT+50TNT+50TQT+51PT+51NT+51QT
SL-VO12=51PPU+51NPU+51QPU
SL-VO13=0
SL-VO14=0
SL-VO15=0
OC-W-79 LOGIC SCHEME
Logic scheme OC-W-79 is intended for feeder breaker applications where nondirectional overcurrent
protection is required. Automatic reclosing is included and is initiated by a protective overcurrent trip or by
an external contact to initiate reclosing (RI). Breaker failure and other control functions such as virtual
switches are not provided in this scheme.
The components of OC-W-79 logic are summarized in Tables 8-5, 8-6, and 8-7. A diagram of OC-W-79 logic
is shown in Figure 8-3. Figure 8-4 shows a one-line drawing for the OC-W-79 logic scheme.
Operation - Protection
All timed (51) and instantaneous (50, 150) overcurrent function blocks are included in this logic scheme. The
overcurrent function block outputs are directed through VO11 to provide a protective trip signal at OUT1.
Overcurrent elements intended for this scheme are phase (P), neutral (N), and Negative Sequence (Q)
protection. A function block is disabled by setting the pickup point at zero in each of the four setting groups.
The 150T function blocks are arranged as high-set instantaneous functions. When a 150T trip occurs, the
recloser is driven to lockout. This scheme also allows the 50TN, 50TQ, 51N, and 51Q function blocks to be
torque controlled by contact input IN3 or virtual switch 243.
Operation - Reclosing
Reclosing logic in OC-W-79 uses a reclose initiate (RI) scheme where each step in the reclosing sequence
is initiated by a protective trip or external initiate signal via IN3. Setting the first reclose time at zero in the
four setting groups will disable the recloser. Reclosing can also be disabled by using IN2. Contact input IN2
is connected to the drive to lockout (DTL) input of the recloser function block. In this scheme, enabling the
recloser after a “one-shot” trip causes the recloser to be in lockout. When the breaker is manually closed,
the relay will time out to a reset condition.
Recloser lockout also occurs if any of the 150TP/N/Q functions trips (typically used for high-set
instantaneous protection). It should be noted that the 150TP/N/Q functions drive both the RI and the DTL
inputs to the recloser function block. The DTL input takes priority over the RI input.
If zone sequence control of the recloser is desired, a logic expression should be entered for the SP-79ZONE
setting that will advance the recloser shot count when a fault is detected, regardless of whether the relay
trips. This is typically the “Protection Picked Up” expression (VO12) in all of the preprogrammed schemes.
Zone sequence uses a BESTlogic expression but is not within the logic settings. Zone sequence
coordination may be enabled by the expression SP-79ZONE=VO12.
OC-W-79 logic provides for the recloser to torque control the 50TP/N/Q functions (typically used for low set
instantaneous protection) during various steps in the reclosing sequence. Setting the recloser Sequence
Controlled Blocking output in the four setting groups is done by using the S#-79SCB commands.
Recloser timing is stopped by the wait input if an overcurrent protection function block is picked up (VO12)
