Sel 411L - Figure 9.3 Circuit Breaker Contact Wear Curve with Relay Settings

P.9.5
Date Code 20151029 Protection Manual SEL-411L Relay
Monitoring and Metering
Circuit Breaker Monitor
Figure 9.3 Circuit Breaker Contact Wear Curve With Relay Settings
Circuit Breaker Contact Wear Curve Details. Circuit breaker
maintenance information from the two end values of Table 9.2 or Figure 9.2
determine set point (B1KASP1, B1COSP1) and set point (B1KASP3,
B1COSP3) for the contact wear curve of Figure 9.3. Set point (B1KASP2,
B1COSP2) is the middle maintenance point in these data. There are two
philosophies for selecting the middle set point. One method places the middle
set point to provide the best “curve-fit” for your plot of the manufacturer’s
circuit breaker maintenance data of Figure 9.2. Another philosophy is to set
the middle point based on actual experience or fault studies of the typical
system faults.
EXAMPLE 9.1 Creating the Circuit Breaker Contact Wear Curve
Acquire the manufacturer’s maintenance information (this example
uses the data of Table 9.2 for Circuit Breaker 1). If you receive the
data in tabular form, plot the manufacturer’s maintenance
information on log/log paper in a manner similar to Figure 9.2.
Choose the left and right set points from the extremes of the curve
you just plotted. Select the left set point on the contact wear curve
corresponding to (B1KASP1, B1COSP1) by setting B1KASP1 := 1.2 and
B1COSP1 := 10000. Plot the right set point (B1KASP3, B1COSP3) by
setting B1KASP3 := 20.0 and B1COSP3 := 12.
Choose the midpoint of the contact wear curve based on your
experience and system fault studies. The majority of operations for a
typical circuit breaker are to interrupt single-line-to-ground faults.
Therefore, plot the midpoint (B1KASP2, B1COSP2) by setting B1KASP2
at or slightly greater than the expected single-line-to-ground fault
current: B1KASP2 := 8.0 and B1COSP2 := 150.
There are two other notable portions of the circuit breaker contact wear curve
in Figure 9.3. The curve is horizontal below the left set point (B1KASP1,
B1COSP1). This is the close/open operation limit regardless of interrupted
current value (for the Example 9.1 circuit breaker, this is at B1COSP1 :=
10000). Some manufacturers call this point the mechanical circuit breaker
service life.
B1COSP2
1 10 100
kA Interrupted per Operation (kA)
Number of Close/Open Operations
10000
1000
100
10
B1COSP3
B1KASP1 B1KASP2 B1KASP3
(B1KASP1, B1COSP1)
(B1KASP2, B1COSP2)
(B1KASP3, B1COSP3)
B1COSP1