9328900990 Rev L BE1-951 Application 8-9
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) and timing. This prevents the reset timer from resetting the reclose function for a situation where a
51 element is just above pickup and the time to trip is longer than the reset time.
Operation - Setting Group Selection
A setting group can be selected automatically or by using the communication ports or the front panel HMI.
Automatic setting group changes are based on current level and duration. Automatic setting group
changes for cold load pickup and/or dynamic setting adjustments are enabled by the SP-GROUP#
command. Setting group changes initiated by contact sensing inputs are not accommodated in this
scheme, but IN2, IN3, or IN4 can be programmed to provide this function.
Operation - Alarms
If the continuous self-test diagnostics of the relay detect an error, failsafe output contact OUTA will
change states and the Relay Trouble LED of the HMI will light. OUTA will also change states if relay
operating power is lost. More information about alarms is provided in Section 6, Reporting and Alarm
Functions.
Outputs OUT4 and OUT5 are assigned to indicate user specified Major or Minor alarms. OUT4 indicates
Minor alarms and OUT5 indicates Major alarms. The user has the ability to specify which alarms are
announced as Major or Minor alarms. When an alarm is detected, the appropriate front panel LED will
light to indicate the alarm. Note that some alarms are non-latching and will clear when the alarm condition
goes away. Other alarms require a reset either by operating the front panel Reset pushbutton or by
issuing ASCII commands through a communication port. More information about alarms is provided in
Section 6, Reporting and Alarm Functions.
NOTE
When using OUT1 through OUT5 as alarm outputs, remember that these outputs
do not have normally closed, failsafe output contacts.
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