BECKWITH ELECTRIC M-6280A, Instruction Book

Page: 287 / 462

M-6280A Instruction Book
4–96
Bank/Switch Failed Measured Current Level 1
Or Level 2 Enabled
If either Level 1 or Level 2 alone is enabled and set
to a value of current that is in the range of 1 to 200
Amps, the control has the capability of determining
two types of failures:
• Failed Cap Bank Switch (if the bank is
Open)
• Open Phase/Failed Cap Bank Switch (if
the bank is Closed).
The current value chosen is dependent on the
size of the capacitor bank and the line voltage of
the circuit (see Table 4-5). This is used to detect
a single switch stuck in the closed position when
the bank has been commanded to Open. When
this occurs, the level of unbalanced current seen
in the neutral is typically in the range referenced in
Table 4-5.
KVAr/0
L - N Voltage
4160 V 7.2 kV 19.9 kV
100 24.04 A 13.89 A 5.03 A
200 48.08 A 27.78 A 10.05 A
300 72.12 A 41.67 A 15.08 A
400 96.15 A 55.56 A 20.10 A
Table 4-5 Calculated Values of Unbalanced
Current in the Cap Bank Neutral
Likewise, if the capacitor bank is Open and a
command to Close is issued, and Level 1 or Level
2 current has been exceeded, it could be the result
of a switch that did not close completely or an open
phase capacitor or a blown fuse. In this scenario,
two of the capacitor bank switches would be closed
.
The neutral unbalance current is the same whether
one or two phases are closed. The value is only
dependent on the kVAr size of the capacitor and the
line voltage. Table 4-5 is again referenced.
If
either failure mode occurs, the control can be
programmed to retry the previous operation, or
to reverse the previous operation, or both. In the
case where both retry and reverse operations
are enabled, the retry operation will always be
performed before the reverse operation, and each
operation will only be performed once. There will
not be retry/reverse operations (due to neutral
current) if the same repeated Close/Open command
is detected. Retry and Reverse operations are
applicable only in Auto and Remote modes.
Bank/Switch Failed Measured Current Level 1
And Level 2 Enabled
If the phase capacitors are large enough to be
constructed from multiple segments or packs within
each capacitor can, it may be possible to detect a
pack failure within a can, by setting both current
detection levels.
This is accomplished by setting the Bank/Switch
Failed Level 2 to the value shown in Table 4-5, which
indicates a complete failure or one or two phases
of the bank.
A value can then be chosen for the Bank/Switch
Failed – Level 1 which is a fraction of the current
of Bank/Switch Failed -Level two. To properly set
this value, it is necessary to know the internal
connection geometry of the capacitors being used
in the bank, such that a failure of one of the internal
packs or segments of the capacitor will generate
a Bank/Switch Failed – Level One signal. This will
work if a segment fails open in paralleled segment
internal connection geometry, or if a segment fails
short in a series segment internal connection
geometry for higher voltage capacitors. A short in
a paralleled geometry will open the capacitor phase
fuse, and an open in a series geometry will generate
a Bank/Switch/Failed –Level Two signal.
It is recommended that the user consult the
capacitor manufacture to obtain data on the internal
construction geometry of the capacitors used.
Bank/Switch Failed Level 2
Prior Operation Element
The “Prior Operation” element of the Bank/Switch
Failed Level 2 feature considers detected neutral
current within a prescribed time period (Prior
Operation is considered to be within 60 seconds of
switch operation) and in the event that the detected
neutral current exceeds the Bank/Switch Failed
Level 2 setpoint, activates user selected “Prior
Operation” actions in a specific sequence.
The “Prior Operation” element includes the following
user selectable actions:
• Retry Operation (1 to 9 Attempts)
• Reverse Operation (1 Attempt)
• Block Operation (Block Reset Time Delay
1 to 72 hours)

NOTE : If at any time during the "Prior Operation"
sequence of actions the control is placed
in Manual Mode or detected neutral
current decreases to less than the
Bank/Switch Failed Level 2 setting the
sequence of actions will stop and normal
control operation will resume.