GE Multilin 850

CHAPTER 4: SETPOINTS CONTROL
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 4–399
CTS detection using the Symmetrical Check Method
SYMMETRY CHECK
Range: Disabled, Enabled
Default: Disabled
This setting enables the symmetry check function. This check uses the ratio of minimum
over maximum of the phase magnitude of currents.
SYM QUOTIENT PKP
Range: 0.00 to 1.00 in steps of 0.01
Default: 0.20
The symmetry check quotient Q is the ratio of I
min
/I
max
. Under normal balanced load
conditions, this ratio is close to unity. Under CT failure, one of the phases can drop and
cause the I
min
to drop to 0 causing the symmetry check function to pickup. The quotient
pickup value should be kept lower than 0.5 to allow for unbalance between the phase
currents.
SYM MIN CURRENT
Range: 0.050 to 30.000 in steps of 0.001
Default: 0.100 x CT
This setting is used to compare the I
max
against the minimum current. For the quotient
to be calculated, the I
max
must be above the minimum current level. This avoids
nuisance alarms during low currents and current transformer measurement errors. As
long as one of the phases is higher than the minimum current level, the quotient is
calculated.
BLOCK
Range: Off, Any FlexLogic operand
Default: Off
OUTPUT RELAY X
For details see Common Setpoints
.
EVENTS
Range: Disabled, Enabled
Default: Enabled
TARGETS
Range: Disabled, Self-Reset, Latched
Default: Latched