GE L30 Instruction Manual page 254

5.6 GROUPED ELEMENTS
• CURRENT DIFF CT TAP 1 and CURRENT DIFF CT TAP 2: These settings adapt the remote terminal 1 or 2 (commu-
nication channel) CT ratio to the local ratio if the CT ratios for the local and remote terminals are different. The setting
value is determined by CT
referred to as the CT primary rated current). Ratio matching must always be performed against the remote CT with the
maximum CT primary defined by the
See the Current differential settings application example in chapter 9 for additional details.
• CURRENT DIFF RESTRAINT 1 and CURRENT DIFF RESTRAINT 2: These settings select the bias characteristic for
the first and second slope, respectively.
• CURRENT DIFF BREAK PT: This setting is used to select an intersection point between the two slopes.
• CURRENT DIFF GND FUNCTION: This setting enables and disabled the 87LG neutral differential element, which may
be used 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 dif-
ferential 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 are equal at all ter-
minals. Refer to the Applications of settings chapter for additional details.
• CURRENT DIFF GND PICKUP: This setting specifies the pickup threshold for neutral current differential element.
• CURRENT DIFF GND RESTRAINT: This setting specifies the bias characteristic for the neutral current differential ele-
ment.
• CURRENT DIFF GND DELAY: This setting specifies the operation delay for the neutral current differential element.
Since this element is used to detect high-resistive faults where fault currents are relatively low, high-speed operation is
5
usually not critical. This delay will provide security against spurious neutral current during switch-off transients and
external fault clearing.
• CURRENT DIFF DTT: This setting enables and disables the sending of a DTT by the current differential element on
per single-phase basis to remote relays. To allow the L30 to restart from master-master to master-slave mode (very
important on three-terminal applications),
• CURRENT DIFF KEY DTT: This setting selects an additional protection element (besides the current differential ele-
ment; for example, distance element or breaker failure) which keys the DTT on a per three-phase basis.
For the current differential element to function properly, it is imperative that all L30 relays on the protected
line have exactly identical firmware revisions. For example, revision 5.62 in only compatible with 5.62, not
NOTE
5.61 or 5.63.
5-118
/ CT for local and remote terminal CTs (where CT
prim_rem prim_loc
CURRENT DIFF SIGNAL SOURCE 1
must be set to "Enabled".
CURR DIFF DTT
L30 Line Current Differential System
prim_rem
through
CURRENT DIFF SIGNAL SOURCE 4
5 SETTINGS
/ CT is
prim_loc
settings.
GE Multilin