8-24
Application
BE1-951
Normal Operation - Protection
All timed and instantaneous overcurrent function blocks are enabled in this scheme. Overcurrent function
blocks are directed through VO11 to provide a protective trip signal at OUT1. The breaker failure function
will also re-trip OUT1 once picked up via BFPU.
The 150T function blocks are arranged as high-set instantaneous functions that drive the recloser to lockout
when they trip. Each overcurrent function block can be disabled individually by a pickup setting of 0 in each
of the four setting groups. This scheme also allows the 50TN, 50TQ, 51N, and 51Q function blocks to be
torque controlled by using either IN3 or virtual switch 243.
Normal Operation - Reclosing
FDR-W-IL reclosing logic uses a reclose initiate (RI) scheme where each step in the reclosing sequence is
initiated by a protective trip.
Setting the first reclose time at zero will disable the recloser function block. Reclosing can also be disabled
by either IN2 or virtual switch 143, which 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 will cause the recloser to be in
lockout. 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/Q functions (typically used for high-set instantaneous
protection) trip or a breaker failure trip (BFT) occurs. 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 which is VO12 in all preprogrammed logic
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.
FDR-W-IL 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. The recloser sequence-controlled
blocking output is set in the four setting groups using the S#-79SCB commands.
Recloser timing is stopped by the wait input if an overcurrent protection function block is picked up 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.
Initiation of the recloser function block by external relaying is not accommodated in this logic scheme.
Normal 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. Automatic setting
group change logic can be enabled by virtual switch 43.
Normal Operation - Bus Protection
When any of the feeder relay overcurrent function blocks are picked up, OUT4 closes. The signal from OUT4
is intended for connection to IN2 of an upstream BE1-951 using BUS logic. When the upstream relay
recognizes an external contact closure on IN2, the upstream relay will block its 50T elements that are set
to trip the bus breaker or bus lockout relay (OUT3 of BUS relay). If the fault is not on a feeder, the 50T
elements of the bus relay are not blocked. Bus relay 50T elements are typically set with a 2 to 4 cycle time
delay to provide a minimal coordination interval for the feeder relay OUT4 to close. Should there be a
problem with the blocking logic, the bus relay 51 functions are not blocked to allow bus fault clearing with
a traditional coordination interval.
When used to provide high-speed overcurrent protection for the substation bus, it is recommended that all
51 function timing curves be set for instantaneous reset.
