Schweitzer Engineering SEL-387-0, Instruction Manual

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5.9
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Metering and Monitoring
Breaker Monitor
Breaker Monitor
The SEL-387 breaker monitoring function is intended to capture information
on the number of operations and total interrupted current for up to four
breakers. These data are used to estimate the amount of contact wear per pole,
based on a wear curve input by the user, and derived from the breaker
manufacturer maintenance curves. Separate settings for each breaker
determine under what conditions the monitoring function is initiated for that
breaker. The breaker monitoring function is capable of differentiating between
an internal trip, generated by units associated with the winding where the
breaker is applied, and an external trip, initiated by units from another
winding, another relay, or control contact. This information will assist the user
in determining when to schedule maintenance of the breakers.
Breaker Monitor
Description and
Initiation Setting
The breaker monitor function has one initiation setting for each breaker. The
BKMON1 through BKMON4 settings, in the Global/Relay settings area, are
SEL
OGIC
control equations, using Relay Word bits to initiate the monitor. The
BKMON n settings look for rising edges (transition from logical 0 to logical 1)
as an indication to read in current values. Currents are read 1.5 cycles after
initiation as symmetrical rms current and sent to the monitor IA, IB, and IC
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 (TR n ), which is
associated with the particular Breaker n that BKMON n 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, 3, or 4) 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 make the following setting:
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-387, BKMON
n 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 internal comparison with TRIP1 is then made to sort out internal
versus external trips.