20 S&C Instruction Sheet 1041-540
Switch Control Operation
The switch control keeps a record of each recognized event, the assumed cause of the
event, and any action taken. The switch control logs all events, regardless of the position
of the automatic operation ENABLE/DISABLE switch and REMOTE/LOCAL switch.
The switch control maintains three separate, chronological logs of event data. Infor-
mation is stored in these logs in a circular fashion; the newest entry always overwrites
the oldest. (The switch control logs each event with millisecond timestamping and 6.25
millisecond resolution.)
The first log is a “sequence of events” buffer. Each record in this log represents one
fault event (for example, an
Overcurrent
condition followed by voltage loss) and/or a
fault-related action taken by the switch control (for example, the line switch opened
because of a
Phase Imbalance
condition). The information in this log is displayed on the
IntelliLink software
OVERCURRENT FAULT
:
Fault Events
screen and the LCD screen.
Overcurrent Data
Logging
The switch control checks the voltage on all three phases at 50-millisecond intervals.
Any voltage drop below the
Loss of Voltage Threshold
setpoint is considered a voltage
outage.
Voltage Loss
Detection
The
Inrush Restraint
feature prevents phase or ground overcurrent conditions, which
can occur during outage restoration (hot or cold load pickup) from falsely indicating a
“fault.” It also applies when the switch is closed from the faceplate or via SCADA while
power is present. The
Current Inrush Restraint Multiplier
feature enables the switch
control to differentiate between moderate overcurrents (caused by cold load pickup) and
large overcurrents (caused by a fault condition) during the Inrush Restraint period. See
S&C Instruction Sheet 1041-572 for additional information.
The
Inrush Restraint
feature is applied as follows:
(a) During a voltage outage, the switch control continuously monitors the switch
status, the RMS voltage sensors, and the phase overcurrent detectors for any
indication that the outage has ended
(b) When voltage rises above the L
oss of Voltage Threshold
setpoint on any phase
or overcurrent is detected on any phase, the switch control checks the switch
position
(c) If the switch is closed, the switch control starts the
Phase Current Inrush
Restraint
timer and the
Ground Current Inrush Restraint
timer
(d) If both
Current Inrush Restraint Multiplier
values are set to
TimeBlock
mode, the switch control ignores all overcurrent conditions until the
Inrush
Restraint
timers expire
If one or both
Current Inrush Restraint Multiplier
values are set to something
other than
Time Block
mode, the switch control considers any overcurrent
condition that exceeds the specified multiplier value to be a “fault.” See the “Phase
Overcurrent Detection” and the “Ground Overcurrent Detection” sections on page
19 for details.
(e) After the inrush restraint timers expire, the switch control responds to
overcurrent conditions in the normal manner (See the “Phase Overcurrent
Detection” and the “Ground Overcurrent Detection” sections on page 19 for
details.)
Note:
If the “Inrush Restraint” times are set to “0”, no inrush restraint occurs.
Inrush Restraint
The switch control’s response to an overcurrent condition or voltage loss depends on
the settings in effect when the event occurs. For example, the values selected for the
Fault Detection Current Level
and
Fault Duration Time Threshold
setpoints
determine whether the switch control recognizes an overcurrent event as a “fault.” The
Automatic Operation
features enabled, and the position of the faceplate automatic
operation ENABLE/DISABLE switch, determine what the switch control will do when a
recognized “fault” occurs.
Overcurrent and
Voltage Loss Events
