ABB RET670 - Page 253

RFPP 1.6 Zload£ ×
load
1.6 Z£ ×RFPP
EQUATION579 V2 EN (Equation 168)
Equation 168 is applicable only when the loop characteristic angle for the phase-to-
phase faults is more than three times as large as the maximum expected load-
impedance angle. More accurate calculations are necessary according to equation
169.
RFPP 1.6 Z
loadmin
cos J
R1PP
X1PP
---------------– sin J×× ×£
EQUATION580 V1 EN (Equation 169)
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 Power swing detection (ZMRPSB, 68) function.
Load impedance limitation, with load encroachment function activated
The parameters for load encroachment shaping of the characteristic are found in the
description of the phase selection with load encroachment function, section
"Setting
guidelines". If the characteristic for the impedance measurement is shaped with the
load encroachment algorithm, the parameter RLdFw and the corresponding load angle
ArgLd must be set according to the minimum load impedance.
Setting of minimum operating currents
The operation of the distance function can be blocked if the magnitude of the currents
is below the set value of the parameter IMinPUPP and IMinPUPG.
The default setting of IMinPUPP and IMinPUPG is 20% of IBase where IBase is the
chosen base current for the analog input channels. The value has 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 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 IMinOpIR
that will block the phase-ground loop if the 3I0<IMinOpIR. The default setting of
IMinOpIR is 5% of the IED base current IBase.
The minimum operating fault current is automatically reduced to 75% of its set value,
if the distance protection zone has been set for the operation in reverse direction.
1MRK504116-UUS C Section 3
IED application
247
Application manual