8-16
Application
BE1-951
Operation - Protection
All overcurrent function blocks are enabled in this scheme. These functions include timed (51) and
instantaneous (50, 150) overcurrent protection. 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 tripped, these functions
drive the recloser to lockout. This scheme also allows the 50TN, 50TQ, 51N, and 51Q function blocks to be
torque controlled by using either IN3 or virtual switch 243.
Operation - Reclosing
OC-W-CTL logic 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 setting at zero in each of
the four setting groups will disable the recloser function block. Reclosing can also be disabled by energizing
IN2, which is connected to the drive to lockout (DTL) input of the recloser function block. When the breaker
is manually closed, the relay will time out to a reset condition.
Drive to lockout also occurs if any of the 150TP, N, or Q functions trip (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 close and
the Relay Trouble LED of the HMI will light. OUTA will also close 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.
