Schweitzer Engineering SEL-387-0, Instruction Manual

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4.19
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Control Logic
Trip and Close Logic
serial port, or if (2) input IN104 has been energized via an external SCADA,
recloser, or control switch contact, for example. CL1 does not directly assert
CLS1 but acts as one input to the AND gate at the center. The other input to
the AND gate is a negated OR gate output which asserts whenever any of the
unlatching functions is in effect. Thus, unlatch elements take precedence over
the close command elements.
Assuming no unlatch elements are asserted, assertion of CL1 produces
assertion of the output Relay Word bit CLS1. CLS1 seals itself in via the OR
gate at the top and begins to drive the output contact OUT105 (=CLS1),
leading to the Breaker 1 closing circuit. CLS1 can also be used in other
SEL
OGIC
control equations. CLS1 will remain asserted, and
OUT105
will
remain closed, until the close logic is unlatched by one of three means:
assertion of the ULCL1 setting, closure of the breaker 52a auxiliary contact,
or a Close Failure Detection. These three functions are inputs to the OR gate at
the mid-left.
The ULCL1 SEL
OGIC
control equation setting defines conditions for
unlatching the close logic. If CL1 is not asserted when ULCL1 asserts,
ULCL1 effectively “blocks” the close logic. If CL1 should assert after ULCL1
has been asserted, it effectively will be ignored, and CLS1 will not assert. If
CL1 has asserted before ULCL1 and the closing process has begun, assertion
of ULCL1 will unseal CLS1 and interrupt the process. In our example,
ULCL1 = TRIP1 + TRIP4. That is, if a Winding 1 overcurrent trip, or a high-
speed differential trip has been initiated, ULCL1 will prevent the close process
from starting, or it will prevent it from going to completion if it has already
begun.
Under normal circumstances, the second means of unlatching occurs. This is
the closure of the Breaker 1 52a contact. The close logic setting 52A1 =
IN101. When CLS1 asserts,
OUT105 closes and the breaker begins to close.
When the breaker closing is complete, the 52a contact closes, duplicating the
operation of the breaker contacts themselves, and effectively indicating that
the breaker is closed. The 52a contact is wired to
IN101 . When IN101 asserts, the
equation 52A1 asserts and unlatches the close logic, deasserting CLS1 and
opening
OUT105
. The close process is now complete. (Presumably, interruption
of the current in the closing circuit has been accomplished via a breaker 52b
contact, and not by
OUT105 .)
The third means of unlatching is a Close Failure Detection. This function can
be set OFF if necessary. This function is useful in the event the breaker does
not close in response to energization of the closing circuit. This might be the
result of electrical problems or mechanical binding or breakage. With the
breaker not moving, CLS1 will remain asserted and
OUT105 will stay closed for
an extended period, possibly resulting in an electrical fire, system damage, or
injury to personnel. Within the logic when CLS1 asserts, an input is also sent
to the AND gate at the bottom. The second AND input is 1 if the Close Failure
detection timer (CFD) is set to some value, and 0 if CFD is set to OFF. In our
example, we have selected CFD = 60 cycles (one second). With CFD set to
some value, a timer is started. At the expiration of CFD, an output is asserted
as Relay Word bit CF1T. This bit is pulsed for one processing interval. It is
sent to the OR gate for the unlatch functions and interrupts the closing
process. This prevents the closing circuit from being energized too long. It
also creates the possibility that the OUT105 contact may be damaged by
interrupting the closing circuit current flow. However, the emergency nature of
the situation generally would be worth the risk. The CFT1 bit might also be
used to set a SEL
OGIC
control equation Latch Bit to close a contact, informing
a SCADA system of the aborted closure attempt.