Schweitzer Engineering Laboratories SEL-311L, Instruction Manual, Page: 311 / 734

Date Code 20010625 Breaker Monitor and Metering Functions 8-7
SEL-311L Instruction Manual
Breaker Monitor Operation Example
As stated earlier, each phase (A, B, and C) has its own breaker maintenance curve. For this
example, presume that the interrupted current values occur on a single phase in Figure 8.4
through Figure 8.7. Also, presume that the circuit breaker interrupting contacts have no wear
initially (brand new or recent maintenance performed).
Note in the following four figures (Figure 8.4 through Figure 8.7) that the interrupted current in a
given figure is the same magnitude for all the interruptions (e.g., in Figure 8.5, 2.5 kA is
interrupted 290 times). This is not realistic, but helps in demonstrating the operation of the
breaker maintenance curve and how it integrates for varying current levels.
0 Percent to 10 Percent Breaker Wear
Refer to Figure 8.4. 7.0 kA is interrupted 20 times, pushing the breaker maintenance curve from
the 0 percent wear level to the 10 percent wear level.
Compare the 100 percent and 10 percent curves and note that for a given current value, the 10
percent curve has only 1/10 of the close/open operations of the 100 percent curve.
10 Percent to 25 Percent Breaker Wear
Refer to Figure 8.5. The current value changes from 7.0 kA to 2.5 kA. 2.5 kA is interrupted 290
times (290 close/open operations = 480 - 190), pushing the breaker maintenance curve from the
10 percent wear level to the 25 percent wear level.
Compare the 100 percent and 25 percent curves and note that for a given current value, the 25
percent curve has only 1/4 of the close/open operations of the 100 percent curve.
25 Percent to 50 Percent Breaker Wear
Refer to Figure 8.6. The current value changes from 2.5 kA to 12.0 kA. 12.0 kA is interrupted
11 times (11 close/open operations = 24 - 13), pushing the breaker maintenance curve from the
25 percent wear level to the 50 percent wear level.
Compare the 100 percent and 50 percent curves and note that for a given current value, the 50
percent curve has only 1/2 of the close/open operations of the 100 percent curve.
50 Percent to 100 Percent Breaker Wear
Refer to Figure 8.7. The current value changes from 12.0 kA to 1.5 kA. 1.5 kA is interrupted
3000 times (3000 close/open operations = 6000 - 3000), pushing the breaker maintenance curve
from the 50 percent wear level to the 100 percent wear level.
When the breaker maintenance curve reaches 100 percent for a particular phase, the percentage
wear remains at 100 percent (even if additional current is interrupted), until reset by the
BRE R
command (see View or Reset Breaker Monitor Information that follows later). Current and trip
counts continue to be accumulated, until reset by the BRE R command.
Additionally, logic outputs assert for alarm or other control applications—see the following
discussion.