Additional security logic for differential protection
LDRGFC
GUID-8F918A08-E50E-4E7B-BDCA-FF0B5534B289 v3
Additional security logic for differential protection
(LDRGFC) can help the security of the protection
especially when the communication system is in
abnormal status or for example when there is
unspecified asymmetry in the communication link. It
helps to reduce the probability for mal-operation of the
protection. LDRGFC is more sensitive than the main
protection logic to always release operation for all faults
detected by the differential function. LDRGFC consists
of four sub functions:
• Phase-to-phase current variation
• Zero sequence current criterion
• Low voltage criterion
• Low current criterion
Phase-to-phase current variation takes the current
samples as input and it calculates the variation using
the sampling value based algorithm. Phase-to-phase
current variation function is major one to fulfill the
objectives of the startup element.
Zero sequence criterion takes the zero sequence current
as input. It increases the security of protection during
the high impedance fault conditions.
Low voltage criterion takes the phase voltages and
phase-to-phase voltages as inputs. It increases the
security of protection when the three-phase fault
occurred on the weak end side.
Low current criterion takes the phase currents as inputs
and it increases the dependability during the switch
onto fault case of unloaded line.
The differential function can be allowed to trip as no
load is fed through the line and protection is not
working correctly.
Features:
• Startup element is sensitive enough to detect the
abnormal status of the protected system
• Startup element does not influence the operation
speed of main protection
• Startup element would detect the evolving faults, high
impedance faults and three phase fault on weak side
• It is possible to block the each sub function of startup
element
• Startup signal has a settable pulse time
4.
Impedance protection
Distance measuring zone, quadrilateral
characteristic ZMQPDIS, ZMQAPDIS
M13787-3 v13
The line distance protection is an up to five (depending
on product variant) zone full scheme protection function
with three fault loops for phase-to-phase faults and
three fault loops for phase-to-earth faults for each of
the independent zones. Individual settings for each zone
in resistive and reactive reach gives flexibility for use as
back-up protection for transformer connected to
overhead lines and cables of different types and lengths.
ZMQPDIS together with Phase selection with load
encroachment FDPSPDIS has functionality for load
encroachment, which increases the possibility to detect
high resistive faults on heavily loaded lines, as shown in
figure
.
en05000034.vsd
R
X
Forward
operation
Reverse
operation
IEC05000034 V1 EN-US
Figure 9.
Typical quadrilateral distance protection zone with
Phase selection with load encroachment function
FDPSPDIS activated
The independent measurement of impedance for each
fault loop together with a sensitive and reliable built-in
phase selection makes the function suitable in
applications with single-phase autoreclosing.
Built-in adaptive load compensation algorithm prevents
overreaching of zone 1 at load exporting end at phase-
to-earth faults on heavily loaded power lines.
The distance protection zones can operate
independently of each other in directional (forward or
reverse) or non-directional mode. This makes them
suitable, together with different communication
schemes, for the protection of power lines and cables in
1MRK 504 155-BEN F
Transformer protection RET670 2.1 IEC
ABB
27
