Date Code 20020129
Metering and Monitoring
5-11
SEL-387E Instruction Manual
current accumulators. The trip counter is also advanced by one count. There are separate current
accumulators and trip counters for internal and external trips.
An internal trip is defined as one initiated by the trip equation (TRn), which is associated with
the particular Breaker n that BKMONn is monitoring. The monitor logic examines, for example,
the status of the TRIP1 variable at the time the BKMON1 setting equation is asserted. If the
TRIP1 variable is asserted when BKMON1 asserts, the trip count and the currents measured are
recorded as internal. If TRIP1 is not asserted when BKMON1 asserts, the trip and currents are
recorded as external. A trip initiated by any other winding elements (Windings 2 or 3) or the
differential element is regarded as external, even though it originates within the same relay.
In our example transformer application we want Breaker 1 to trip for its own overcurrent
elements (OUT101 = TRIP1; TR1 = 51P1T+51Q1T) or for a differential trip (86T
device trip via OUT104 = TRIP4; TR4 = 87R+87U). In this case we set
BKMON1 = TRIP1 +
TRIP4
. Winding 1 overcurrent trips (TRIP1) will be credited to the internal trip counter and
current accumulators, and differential trips (TRIP4) will appear as external trips.
In order to capture trip information for other Breaker 1 trips initiated by devices other than the
SEL-387E Relay, BKMONn must be set to sense these trips. This can be done, for example, by
using an input to monitor the trip bus for the given breaker. This is illustrated in Figure 5.4,
where IN106 is connected to the Breaker 1 trip bus and asserts for any trip from any source.
Setting
BKMON1 = IN106
ensures that the monitor will initiate for any Breaker 1 trip. The
monitor then compares IN106 with TRIP1 to sort internal and external trips.
Figure 5.4: Trip Bus Sensing With Relay Input
Breaker Wear Curve Description and Settings
Based on maintenance curves supplied by manufacturers of the breakers, a contact wear curve
for each breaker is constructed (Figure 5.5).
