EQUATION792 V2 EN-US (Equation 218)
This equation is applicable only when the loop characteristic angle for the single
phase-to-earth faults is more than three times as large as the maximum expected
load-impedance angle. More accurate calculations are necessary according to the
equation below:
min
21 0
0.8 cos sin
21 0
load
RZx R Zx
RFPEZx Z
XZx X Zx
EQUATION578 V5 EN-US (Equation 219)
Where:
ϑ is a maximum load-impedance angle, related to the minimum load impedance conditions.
All this is applicable for all measuring zones when no power swing detection
element is in the protection scheme. Use an additional safety margin of
approximately 20% in cases when a power swing detection element is in the
protection scheme, refer to the description of the power swing detection
(ZMRPSB) function.
8.5.3.8 Load impedance limitation, with load encroachment function
activated
SEMOD154704-129 v1
The parameters for load encroachment shaping of the characteristic are found in the
description of the phase selection with load encroachment function, section
"Resistive reach with load encroachment characteristic". If the characteristic for the
impedance measurement shall be shaped with the load encroachment algorithm, the
parameter OperationLdCmp in the phase selection has to be switched On.
8.5.3.9 Setting of minimum operating currents
SEMOD154704-132 v2
The operation of the distance function will be blocked if the magnitude of the
currents is below the set value of the parameter IMinOpPE.
The default setting of IMinOpPE is 20% of IBase where IBase is the chosen base
current for the analog input channels. The value have been proven in practice to be
suitable in most of the applications. However, there might be applications where it
is necessary to increase the sensitivity by reducing the minimum operating current
down to 10% of the IED base current. This happens especially in cases, when the
IED serves as a remote back-up protection on series of very long transmission
lines.
If the load current compensation is activated, there is an additional criteria
IMinOpIN that will block the phase-earth loop if the 3I0<IMinOpIN. The default
setting of IMinOpIN is 5% of the IED base current IBase.
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 281
Application manual
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