The negative sequence detection algorithm, based on the negative-sequence
measuring quantities is recommended for use in isolated or high-impedance earthed
networks: a high value of voltage 3U
2
without the presence of the negative-sequence
current 3I
2
is a condition that is related to a fuse failure event.
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.
14.2.3
Setting guidelines
14.2.3.1
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 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.
14.2.3.2
Setting of common parameters
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
1MRK 502 071-UEN -
Section 14
Secondary system supervision
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
473
Application manual
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