Schweitzer Engineering Laboratories SEL-387E, Инструкция по эксплуатации

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Date Code 20020129 Metering and Monitoring 5-13
SEL-387E Instruction Manual
To determine the constants K and
a
for a given segment, any two current-operations pairs in that
segment must be known. For any given pairs (I1, O1) and (I2, O2), the alpha constant is
determined by the equation:
Ü
Ý
Û
Ì
Í
Ë
Ü
Ý
Û
Ì
Í
Ë
= a
2 I
1 I
log
2 O
1 O
log
10
10
The K constant can be found by back substitution:
a
=
1 I
1 O
K , or
a
=
2 I
2 O
K
Here, we can use the endpoint pairs (BnKAP1, BnCOP1) and (BnKAP2, BnCOP2) to determine
the equation that applies between these two input points and pairs (BnKAP2, BnCOP2) and
(BnKAP3, BnCOP3) for the equation between the latter two points.
In Figure 5.5, for example, the two segments have the following equations:
( )
214 . 2
I • 14972 I O
-
=
and
( )
756 . 2
I • 46284 I O
-
=
For a particular value of I in kA, the calculated value O(I) represents 100 percent wear of the
breaker contacts. Thus, the incremental percent wear for one trip operation at the defined current
level is 100 / O(I) percent. For I < BnKAP1, O(I) = BnCOP1. For BnKAP1 < I < BnKAP2, O(I)
is calculated by the first equation. For BnKAP2 < I < BnKAP3, O(I) is calculated by the second
equation. For I > BnKAP3, O(I) = 0 and contact wear = 100 percent.
Because the breaker monitor calculates and accumulates current by phase, the wear for each pole
of the breaker is calculated separately, using the same wear curve as a basis. Thus, over time,
the cumulative percent wear for each of the three poles will be different. If a breaker already has
some estimated wear when the relay is first applied, the user can preload a separate amount of
wear for each pole of the breaker using the serial port command
BRE W n (or BRE n W ).
Integer values of percent wear up to 100 percent are accepted by the relay. The incremental wear
for the next interruption, and all subsequent interruptions, is added to the prestored value for a
total wear value.
When the cumulative wear on any breaker pole reaches 100 percent, Relay Word bits are set to
logical 1 for the particular pole, as well as for the breaker containing that pole. For example, for
Breaker n, the Relay Word bits for the three poles are designated BCWAn, BCWBn, and
BCWCn; for the breaker itself, Relay Word bit BCWn is set to logical 1 if any of the individual
pole bits is set to logical 1. These bits may be used for alarm or display purposes, to alert the
user that breaker inspection and maintenance may be required.
After breaker maintenance is performed or a new breaker installed, the breaker monitor
operation counters, cumulative interrupted currents by pole, and percent wear by pole should be
reset to zero. This can be done via the
BRE R n (or BRE n R ) serial port command or from the
front panel via the OTHER pushbutton menu.
Both the BRE W n and BRE R n commands can be executed from Access Level B or 2.