ABB RET670 Applications Manual page 310

Section 3
IED application
304
This equation is applicable only when the loop characteristic angle for the single phase-
to-ground 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:
é
£ × ×
RFPE 0.8 Z
ê
ë
load min
EQUATION578 V3 EN
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, 78) 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
reach with load encroachment
measurement shall be shaped with the load encroachment algorithm, the parameter
OperationLdCmp in the phase selection has to be switched On.
Setting of minimum operating currents
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 analogue 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-ground loop if the 3I0<IMinOpIN. The default setting of
IMinOpIN 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.
× +
2 R 1 R 0
¶ - ×
cos sin
× +
2 X 1 X 0
characteristic". If the characteristic for the impedance
1MRK504116-UUS C
ù
¶
ú
û
Application manual
(Equation 233)
"Resistive