ABB Relion REQ650, Руководство по применению

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The negative sequence detection algorithm, based on the negative-sequence
measuring quantities, a high value of voltage 3U
2
without the presence of the
negative-sequence current 3I
2
, is recommended for use in isolated or high-impedance
earthed networks.
The zero sequence detection algorithm, based on the zero sequence measuring
quantities, a high value of voltage 3U
0
without the presence of the residual current
3I
0
, is recommended for use in directly or low impedance earthed networks. 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.
9.2.3 Setting guidelines
9.2.3.1 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 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,
UBase and IBase respectively. Set
UBase to the primary rated phase-phase voltage of the potential voltage transformer
and IBase to the primary rated current of the current transformer.
9.2.3.2 Setting of common parameters
GlobalBaseSel : Selects the global base value group used by the function to define
( IBase ), ( UBase ) and ( SBase ).
The settings of negative sequence, zero sequence and delta algorithm are in percent of
the global base voltage and global base current for the function,
UBase and IBase
respectively.
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 the global
parameter
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
1MRK 505 291-UEN A
Section 9
Secondary system supervision
175
Application manual