1011-530
22
from shorting out a series group is:
Therefore, the desired gross overvoltage lockout level is:
Alarm Level
The alarm lets you choose a voltage level below lockout. When an alarm becomes
active, you can choose whether to continue operating the bank (deferring replacement
of the failed unit until a convenient time) or to replace the failed unit sooner (minimiz-
ing the time that the surviving capacitor units are exposed to overvoltage and thus
reducing the likelihood that marginal units will fail prematurely).
You should set the alarm level to approximately half of the value of the tap-point volt-
age percent imbalance resulting from the isolation of one capacitor unit (
U
tp
); if the
number of series groups is odd, set the value to half of the lower
U
tp
.
For “Formula Method – Example 1” on page 19, the alarm setting would be:
For “Formula Method – Example 2” on page 20, the alarm setting would be:
Coordinating Bank Lockout and Individual Capacitor Unit Fuses
It is important to coordinate capacitor bank isolation and lockout with the individual
capacitor unit fuses. The control device should not lock out before the fuse of the last-
failing capacitor unit has had sufficient time to operate. If the fuse does not operate,
there will be no indication of which capacitor unit was in the process of failing.
In general, bank lockout and the individual capacitor unit fuses will be coordinated if
all of the following are true:
•
The lockout and alarm levels are set as described above (graphical method or for-
mula method).
•
The lockout delay time is adequate.
•
The individual capacitor unit fuses use a fusing ratio of 1.25 or less.
U
tp
100
7
1
–
------------
16.67%
=
=
3.70%
16.67%
+
2
-----------------------------------------
10.19%
=
5.26%
2
---------------
2.63%
=
1.28%
2
---------------
0.64%
=
Summary of Contents for BankGuard PLUS
Page 4: ...1011 530 4...
Page 6: ...1011 530 6 Figure 1 Vo versus F P Ungrounded Wye Capacitor Bank...
Page 50: ...1011 530 50...
