Date Code 20080110 Control Logic 4-21
SEL-387E Instruction Manual
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, the logic will effectively ignore CL1 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 will prevent the close process
from going to completion if it has already begun.
Under normal circumstances, the second means of unlatching, closure of the Breaker 1 52a
contact, occurs. 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 to OFF but
is useful in the event the breaker does not close in response to energization of the closing circuit.
This might be due to 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 and sent to the OR gate for the unlatch functions, where
it interrupts the closing process. This interruption prevents the closing circuit from being
energized too long but 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 warrants 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.
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.
In our example inputs IN101 to IN103 are assigned to represent the 52a contacts. That is,
52A1 = IN101, 52A2 = IN102, and 52A3 = IN103. (Note again that inputs appear in the right
side of an equation, outputs on the left side.) The connections for the 52a inputs are shown in
Figure 2.19 in Section 2: Installation.
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