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Date Code 20020129
Control Logic
4-19
SEL-387E Instruction Manual
With the deassertion of TRIP1, OUT101 opens, deenergizing the trip circuit. Presumably, the
trip circuit current has already been interrupted by a breaker 52a contact in series with the trip
coil. Should a failure to trip occur, followed by backup tripping of other breakers, the TR1
setting may deassert and the ULTR1 setting may assert, while the contact continues to carry dc
trip circuit current. This could damage the contact as it tries to interrupt this current. The
emergency nature of the situation might warrant this minor risk, but another choice might be to
program into the ULTR1 setting not only removal of current, but also indication that the breaker
has opened.
Note that TRIP1 will always be asserted as long as TR1 is asserted, regardless of the action of
ULTR1
or the
TARGET RESET
commands, and that TRIP1 will be asserted for an absolute
minimum of TDURD cycles, no matter how short a time TR1 has been asserted. This is the
essence of the trip logic.
At the bottom of Figure 4.7 is an additional OR gate. The four TRIPm Relay Word bits are all
inputs to this gate, and the output is another Relay Word bit TRIPL. TRIPL asserts for any trip
output. It may be useful for other applications of SEL
OGIC
control equations in the SEL-387E
Relay.
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 four trip variables, TR1 to TR4, to define conditions under which a trip will be issued.
This will cover trip conditions for three 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 one to three. 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 5xxxxT 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, because
this would indicate that the definite-time element has timed out. However, because 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.
In general, definition of the TR1 and TR4 variables should include only Relay Word bits that
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 four settings. Exceptions might be bits used for opening the breaker by
command during nonfault conditions, such as the OCn bits or the remote bits, RBn.
When the trip logic is activated, and
one or more Relay Word bits TRIP1 to TRIP4 are set to
logical 1, 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 =
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