The zero sequence detection algorithm, based on the zero sequence measuring
quantities is recommended for use in directly or low impedance earthed networks:
a high value of voltage 3U
0
without the presence of the residual current 3I
0
is a
condition that is related to a fuse failure event. In cases 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.
9.1.3 Setting guidelines
IP15000-1 v1
9.1.3.1 General
M13683-3 v5
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 long 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. Common base IED values for
primary current (IBase), primary voltage (UBase) and primary power (SBase) are
set in Global Base Values GBASVAL. The setting GlobalBaseSel is used to select a
particular GBASVAL and used its base values.
9.1.3.2 Setting of common parameters
M13683-9 v9
Set the operation mode selector Operation to On to release the fuse failure
function.
The voltage threshold USealIn< is used to identify low voltage condition in the
system. Set USealIn< below the minimum operating voltage that might occur
during emergency conditions. We propose a setting of approximately 70% of
UBase.
The drop off time of 200 ms for dead phase detection makes it recommended to
always set SealIn to On 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
Section 9 1MRK 505 388-UEN B
Secondary system supervision
146 Busbar protection REB650 2.2 IEC
Application manual
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