The neutral point reactor is normally designed so that it can be tuned to a position
where the reactive current balances the capacitive current from the network:
1
3
L
C
w
w
=
× ×
EQUATION1272 V1 EN-US
(Equation 263)
ANSI05000216 V2 EN-US
Figure 174:
High impedance grounded network
The operation of high impedance grounded networks is different compared to solid
grounded networks, where all major faults have to be cleared very fast. In high
impedance grounded networks, some system operators do not clear single phase-to-
ground faults immediately; they clear the line later when it is more convenient. In case
of cross-country faults, many network operators want to selectively clear one of the
two ground faults.
In this type of network, it is mostly not possible to use distance protection for detection
and clearance of ground faults. The low magnitude of the ground-fault current might
not give pickup of the zero-sequence measurement elements or the sensitivity will be
too low for acceptance. For this reason a separate high sensitive ground-fault
protection is necessary to carry out the fault clearance for single phase-to-ground fault.
For cross-country faults and when using phase preference, it is necessary to make sure
that the distance protection is operating in the phase-to-earth loops independently,
whenever possible. See guidelines for setting
INReleasePE
.
8.12.2.2
Fault infeed from remote end
GUID-E28CCC52-497F-4B79-9430-8A2155FED936 v4
All transmission and most all sub-transmission networks are operated meshed. Typical
for this type of network is that fault infeed from remote end will happen when fault
occurs on the protected line. The fault current infeed will enlarge the fault impedance
seen by the distance protection. This effect is very important to keep in mind when
both planning the protection system and making the settings.
With reference to figure
, the equation for the bus voltage V
A
at A side is:
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI
371
Application manual
Содержание RELION RET670
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