6-6
Metering and Monitoring
Date Code 20010731
SEL-352-1, -2 Instruction Manual
Use the breaker contact wear function to estimate the amount of contact wear per pole. You can
use this information and the BCW (breaker contact wear alarm) Relay Word bit in a Reliability
Centered Maintenance program. The relay estimates the contact wear based on a simple model
of the breaker manufacturer maintenance curves, number of breaker operations, and total
interrupted current. The curve is a plot of close/open operations versus interrupted currents in
kiloamperes (kA). The total interrupted current is an accumulation of the RMS current (IRMSA,
IRMSB, IRMSC) measured Topen milliseconds after a trip (TRIPA, TRIPB, TRIPC Relay Word
bit).
Use the three points shown in Figure 6.1 to model the breaker maintenance curve. These points
divide the curve into three regions to tailor the curve for a breaker in a particular application.
The first region is intended for low currents, the second for medium currents, and the third for
high currents. This flexibility accommodates mechanical wear resulting from low-current
breaker interruptions and electrical wear resulting from medium and high currents.
KASP1 is kA Set Point 1, while COSP1 is Close/Open Set Point 1. The relay will not accept the
settings unless KASP3>KASP2>KASP1 and COSP1>COSP2>COSP3.
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Figure 6.1: Breaker Maintenance Curve
Breaker contact wear calculation occurs on a per-phase basis (BCWPn where n=A, B, or C) by
adding the percent wear for the latest operation to the previous sum. For example, the breaker
can perform 6200 close/open operations if 3 kA is interrupted each time. Therefore, a single 3
kA operation adds 100 percent (1/6200) = 0.016 percent wear to the breaker. The breaker can
perform 400 close/open operations if 10 kA is interrupted each time. Therefore, a single 10 kA
operation adds 100 percent (1/400) = 0.25 percent wear to the breaker, an accumulated wear of
0.266 percent.
The relay uses the following equation to calculate the contact wear as described above:
( )
(
)
1
k
k
BCWPp
I
K
100
BCWPp
-
a
+
¼
=
Содержание SEL-352-1
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