GE L30 Instruction Manual page 425

CHAPTER 5: SETTINGS
If set to "2-out-of-3," the L30 checks second harmonic level in all three phases individually. If any two phases establish an
inhibiting condition, then the remaining phase is restrained automatically.
If set to "Average", the L30 first calculates the average second harmonic ratio, then applies the inrush threshold to the
calculated average.
This setting specifies the level of second harmonic component in the transformer magnetizing
—
INRUSH INHIBIT LEVEL
inrush current, above which the current differential element is inhibited from operating. The value of the
setting must be taken into account when programming this value. This setting is typically programmed as "20% f
MODE
CURRENT DIFF GND FUNCTION
to detect high-resistive faults. This element uses restrained characteristics to cope with spurious zero-sequence current
during system unbalance and signal distortions. The differential neutral current is calculated as the vector sum of all in-
zone CT input neutral currents. The restraint current is derived as the maximum of phase currents from all terminals
flowing through any individual CT, including breaker-and-a-half configurations. The 87LG neutral differential element is
blocked when the phase current at any terminal is greater than 3 pu, since the phase differential element should operate
for internal faults. To correctly derive the restraint quantity from the maximum through current at any terminal, it is
important that the 87L phase-segregated differential pickup and slope settings be equal at all terminals. See the
Application of Settings chapter for details.
— This setting specifies the pickup threshold for neutral current differential element.
CURRENT DIFF GND PICKUP
CURRENT DIFF GND RESTRAINT
— This setting specifies the operation delay for the neutral current differential element. Since this
CURRENT DIFF GND DELAY
element is used to detect high-resistive faults where fault currents are relatively low, high-speed operation is usually not
critical. This delay provides security against spurious neutral current during switch-off transients and external fault
clearing.
— This setting enables and disables the sending of a direct transfer trip (DTT) by the current differential
CURRENT DIFF DTT
element on per single-phase basis to remote devices. To allow the L30 to restart from master-master to master-slave
mode (very important on three-terminal applications),
— This setting selects an additional protection element (besides the current differential element; for
CURRENT DIFF KEY DTT
example, distance element or breaker failure) that keys the DTT on a per three-phase basis.
For the current differential element to function properly, it is imperative that all L30 devices on the protected line
have identical firmware revisions. For example, revision 5.62 in only compatible with 5.62, not 5.61 or 5.63.
L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
— This setting enables and disabled the 87LG neutral differential element, which can be used
— This setting specifies the bias characteristic for the neutral current differential element.
CURR DIFF DTT
must be "Enabled."
GROUPED ELEMENTS
INRUSH INHIBIT
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