Setting Guidelines - ABB RET670 Applications Manual

1MRK504116-UUS C
3.11.2.2
Application manual
where the line can have a weak-infeed of zero sequence current this function shall be
avoided.
A criterion based on delta current and delta voltage measurements can be added to the
fuse failure supervision function in order to detect a three phase fuse failure. This is
beneficial for example during three phase transformer switching.

Setting guidelines

General
The negative and zero sequence voltages and currents always exist due to different non-
symmetries in the primary system and differences in the current and voltage instrument
transformers. The minimum value for the operation of the current and voltage
measuring elements must always be set with a safety margin of 10 to 20%, depending
on the system operating conditions.
Pay special attention to the dissymmetry of the measuring quantities when the function
is used on longer untransposed lines, on multicircuit lines and so on.
The settings of negative sequence, zero sequence and delta algorithm are in percent of
the base voltage and base current for the function, VBase and IBase respectively. Set
VBase to the primary rated phase-phase voltage of the potential voltage transformer
and IBase to the primary rated current of the current transformer.
Setting of common parameters
Set the operation mode selector Operation to On to release the fuse failure function.
The voltage threshold VPPU is used to identify low voltage condition in the system.
Set VPPU below the minimum operating voltage that might occur during emergency
conditions. We propose a setting of approximately 70% of VBase.
The drop off time of 200 ms for dead phase detection makes it recommended to always
set SealIn to Enabled since this will secure a fuse failure indication at persistent fuse
fail when closing the local breaker when the line is already energized from the other
end. When the remote breaker closes the voltage will return except in the phase that
has a persistent fuse fail. Since the local breaker is open there is no current and the
dead phase indication will persist in the phase with the blown fuse. When the local
breaker closes the current will start to flow and the function detects the fuse failure
situation. But due to the 200 ms drop off timer the output BLKZ will not be activated
until after 200 ms. This means that distance functions are not blocked and due to the
"no voltage but current" situation might issue a trip.
The operation mode selector OpModeSel has been introduced for better adaptation to
system requirements. The mode selector makes it possible to select interactions
between the negative sequence and zero sequence algorithm. In normal applications the
OpModeSel is set to either UNsINs for selecting negative sequence algorithm or
Section 3
IED application
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