Schweitzer Engineering SEL-387-0, Instruction Manual

Page: 204 / 556

6.4
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Setting the Relay
Additional Relay Settings
Trip and Close Logic
The Settings Sheets contain two specific areas highlighting the assignment of
variables for the Trip Logic and Close Logic . These functions, along with
those in the Output Contact Logic area, must be programmed in order for the
relay to take action. Settings in all three areas are SEL
OGIC
control equations.
There are five trip variables to define conditions under which a trip will be
issued. These are named TR1 to TR5. This will cover trip conditions for four
separate breakers, plus one extra for a general trip of all breakers. The settings
for the example transformer application illustrate this.
In the example, TR1 through TR3 are set to respond to overcurrent elements
specific to the winding associated with Breakers 1 to 3. For example, TR1 =
51P1T + 51Q1T. Complete operation of the phase definite-time or
inverse-time elements, or the negative-sequence inverse-time element, will set
the appropriate Relay Word bits 5
xxxx T to one, and TR1 will respond to any
of them. TR1 initiates the Trip Logic, producing output of the logic and
setting of Relay Word bit TRIP1 to one. For tripping Breaker 2, TR2 = 51P2T
+ 51Q2T. For tripping Breaker 3, TR3 = 50P31 + 51P3T. Technically, 50P31T
should have been used, since this would indicate that the definite-time element
has timed out. However, since 50P31 is set for zero delay, or is instantaneous,
there is no reason to wait. For group tripping of all three breakers, TR4 = 87R
+ 87U. This results in a tripping output to an external 86 lockout device, which
then trips the three breakers with separate contacts. This takes place only if a
differential operation, either restrained or unrestrained, is detected. TR5 is not
used, and is set to zero.
In general, definition of the TR1 and TR5 variables should include only Relay
Word bits which remain firmly asserted during a fault, but otherwise are not
asserted. For this reason, rising-edge detection (/), falling-edge detection (\),
and the NOT operator (!) should be avoided for the Relay Word bits used in
these five settings. Exceptions might be bits used for opening the breaker by
command during nonfault conditions, such as the OC
n bits or the remote bits,
RB n .
When the trip logic is activated, and one or more Relay Word bits TRIP1 to
TRIP4 are set to one, a trip can take place. However, in order for this to
happen an output contact must be assigned for each trip. These assignments
are made on the Output Contact Logic setting sheet area. In this case, OUT101
= TRIP1, OUT102 = TRIP2, OUT103 = TRIP3, and OUT104 = TRIP4.
OUT101 to OUT103 go directly to the three breaker trip coils, and OUT104
goes to the 86 operate coil. These connections are shown in
Figure 2.9 .
Corresponding to the five trip variables in the Trip Logic setting area are five
unlatch variables. The variables ULTR1 to ULTR5 define the conditions to
unlatch the seal-in of trip logic that takes place when TR
n goes to one. They
sense when it is appropriate to de-energize the trip circuit. In this case, the
instantaneous overcurrent elements, 50P
n 3, were set very low, and unlatch is
defined as when the phase currents in all three phases drop below the setting.
This is done with the NOT operator. That is, ULTR1 = !50P13, ULTR2 =
!50P23 and ULTR3 = !50P33. ULTR4 = !(50P13 + 50P23 + 50P33), and
unlatches TRIP4 when all phase currents on all windings drop below the 0.5 A
setting. ULTR5 is not used and is set to zero.
In the Close Logic setting area, inputs are defined to represent the 52a
auxiliary contacts from the individual breakers. Defined as well are the four
Close and four Unlatch Close variables, if the closing function is to be used.