CHAPTER 6: SETPOINTS
S3 PROTECTION
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–103
Broken conductor (I1/I2 or 46BC)
The Broken Conductor detection function detects a feeder broken conductor condition or a
single-pole open breaker malfunction condition by checking the phase current input
phasors and the I
2
/ I
1
ratio. In normal and balanced load situations this ratio is zero, while
in broken conductor conditions an unbalance is produced and this ratio increases. The
intention of this function is to detect a single-phase broken conductor only. As such, two-
phase or three-phase broken conductors cannot be detected.
The broken conductor element compares the I
2
/ I
1
ratio against a programmed threshold,
while I
1
is the normal range. To distinguish between a single-phase disappearance and a
system disturbance in all three phases (such as load change, switching, etc.), the broken
conductor element also monitors for a change in only a single phase current.
NOTE
NOTE:
Note that there are several broken conductor scenarios that this element cannot detect.
The broken conductor Pickup flag is asserted when the I
2
/ I
1
ratio is above the I_2/I_1
RATIO setting's value, the positive sequence current is between I_1 MIN and I_1 MAX, and a
single phase current changes by more than 0.05 x CT. The broken conductor Trip flag is
asserted if the element stays picked up for the time defined by the PICKUP DELAY setting.
The element instantaneously drops from pickup without operation if the I
2
/ I
1
ratio
decreases to below 97% to 98% of the pickup value before the time for operation is
reached.
PATH
:
SETPOINTS > S3 PROTECTION > SETPOINT GROUP 1(2) > BROKEN CONDUCTOR
BROKEN CONDUCTOR FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Control
Default: Disabled
For details see
I_2/I_1 RATIO
Range: 20.0% to 100.0% in steps of 0.1%
Default: 20.0%
This setting specifies the ratio of negative-sequence current to positive-sequence
current for element operation. When one phase conductor is broken, the I
2
/ I
1
ratio with
balanced remaining phases is 50%. Thus, usually this setting should be set below 50%
(for example, to 30%).
I_1 MIN
Range: 0.05 to 1.00 x CT in steps of 0.01 x CT
Default: 0.10 x CT
This setting specifies the minimum positive-sequence current supervision level. Ensure
the setting is programmed to a level sufficient to prevent the I
2
/ I
1
ratio from causing
erratic pickup due to a low I
1
signal. However, this setting cannot be set too high since
the broken conductor condition cannot be detected under light load conditions when I
1
is less than the value specified by this setting.
I_1 MAX
Range: 0.05 to 5.00 x CT in steps of 0.01 x CT
Default: 0.10 x CT
This setting specifies the maximum I
1
level allowed for the broken conductor function to
operate. When I
1
exceeds this setting, it is considered a fault. This broken conductor
function should not respond to any fault conditions so normally the setting is
programmed to less than the maximum load current.
