Sel 411L - Page 652

P.9.6
SEL-411L Relay Protection Manual Date Code 20151029
Monitoring and Metering
Circuit Breaker Monitor
Another part of the circuit breaker maintenance curve falls vertically at the
right set point (B1KASP3, B1COSP3). This is the maximum interrupted
current limit (for the Example 9.1 circuit breaker, this is at B1KASP3 := 20.0).
If the interrupted current exceeds setting B1KASP3, the relay sets contact
wear at 105 percent.
EXAMPLE 9.2 I
2
t Criteria Application
Some circuit breaker manufacturers do not provide a circuit breaker
maintenance curve, but specify the accumulated fault current arcing
time (I
2
t) for circuit breaker maintenance. For example,
manufacturer’s data specify I
2
t per phase at 750 kA
2
-seconds for a
particular circuit breaker, at a rated arcing duration for each trip of
1 cycle. The circuit breaker maximum interrupting current rating is
40 kA, and the continuous load current rating is 2 kA.
You can construct the contact wear curve for this circuit breaker from
the specified I
2
t. Choose B1KASP1 := 2.0 (the continuous current
rating) and B1KASP3 := 40.0 (the maximum interrupting current
rating). Choose the middle of the contact wear curve based on
experience and system fault studies. The majority of faults a typical
circuit breaker interrupts are single-line-to-ground faults. Therefore,
set nKASP2 at or slightly greater than the expected
single-line-to-ground fault current (B1KASP2 := 10.0 kA in this
example). From the following equations, calculate these settings
points to obtain the number of close/open operations:
Equation 9.1
Equation 9.2
Equation 9.3
In these equations, t
arc
is the arcing time in seconds; t
arc
= (1/f
NOM
)•
(arc duration in cycles); f
NOM
is the nominal power system frequency
(50 Hz or 60 Hz). These calculations show the number of close/open
operations rounded to the nearest unit.
Preloading Contact Wear Data
Upon the first commissioning of the relay, the associated circuit breakers can
already have some wear. You can preload a separate amount of wear for each
pole of each circuit to preload existing contact wear data. The relay accepts
integer values of percentage wear as great as 100 percent. The relay adds the
incremental contact wear at the next circuit breaker monitor initiation (and at
all subsequent initiations) to the preloaded value to obtain a total wear value.
The limit for reporting circuit breaker contact wear is 150 percent for each
pole.
Program the SELOGIC Control Equations for Trip and Close Conditions
NOTE: In the following discussion,
three elements are specified. There is
one element for each phase:  = A, B,
and C).
Circuit Breaker Monitor Trip Initiation Settings: BM1TRP. The
relay employs SEL
OGIC control equations to initiate the circuit breaker
monitor. For Circuit Breaker 1, this setting is BM1TRP. These SEL
OGIC
control equations use Relay Word bits to determine when the circuit breaker
monitor accumulates circuit breaker operating parameters from phases A, B,
and C. When detecting a rising edge (a transition from logical 0 to logical 1)
of the initiation settings, the relay accumulates the interrupted rms currents
B1COSP1 =
I
2
t

(B1KASP1)
2
• t
arc
----------------------------------------------
750
2
2
• (0.01667 • 1)
-----------------------------------------
:= 11250=
B1COSP2 =
I
2
t

(B1KASP2)
2
• t
arc
--------------------------------------------
750
10
2
• (0.01667 • 1)
-------------------------------------------- := 450=
B1COSP3 =
I
2
t

(B1KASP3)
2
• t
arc
--------------------------------------------
750
40
2
• (0.01667 • 1)
-------------------------------------------- := 28=