R
X
RLd
RLd
LdAngle
LdAngle
LdAngle
LdAngle
en06000404_ansi.vsd
ANSI06000404 V1 EN
Figure 127: Load encroachment of Faulty phase identification with load
encroachment for mho function FMPSPDIS (21) characteristic
The use of the load encroachment feature is essential for long heavy loaded lines, where
there might be a conflict between the necessary emergency load transfer and necessary
sensitivity of the distance protection. The function can also preferably be used on heavy
loaded medium long lines. For short lines the major concern is to get sufficient fault
resistance coverage and load encroachment is not a major problem. So, for short lines, the
load encroachment function could preferably be switched off.
The main settings of the parameters for load encroachment are done in Faulty phase
identification with load encroachment for mho function FMPSPDIS (21). The operation
of load encroachment function is always activated. To deactivate the function, setting
LoadEnchMode should be set off or the setting of RLdFw and RLdRv must be set to a value
much higher than the maximal load impedance.
8.4.2.5 Short line application
The definition of short, medium and long lines is found in IEEE Std C37.113-1999. The
length classification is defined by the ratio of the source impedance at the protected line’s
terminal to the protected line’s impedance (SIR). SIR’s of about 4 or greater generally
define a short line. Medium lines are those with SIR’s greater than 0.5 and less than 4.
Section 8 1MRK 506 369-UUS -
Impedance protection
258 Line distance protection REL670 2.2 ANSI
Application manual
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