ABB RELION RET670, Applications Manual

Page: 675 / 1016

to the voltage instrument transformers, and shall be equipped with auxiliary contacts
that are wired to the IEDs. Separate fuse-failure monitoring IEDs or elements within
the protection and monitoring devices are another possibilities. These solutions are
combined to get the best possible effect in the fuse failure supervision function
(FUFSPVC).
FUFSPVC function built into the IED products can operate on the basis of external
binary signals from the miniature circuit breaker or from the line disconnector. The
first case influences the operation of all voltage-dependent functions while the second
one does not affect the impedance measuring functions.
The negative sequence detection algorithm, based on the negative-sequence measuring
quantities is recommended for use in isolated or high-impedance grounded networks: a
high value of voltage 3V
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 grounded networks: a
high value of voltage 3V
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
IP15000-1 v1
14.2.3.1 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 ( VBase ) 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.
1MRK 504 163-UUS A
Section 14
Secondary system supervision
Transformer protection RET670 2.2 ANSI 669
Application manual