ABB RELION REB670, Руководство по эксплуатации продукта

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saturated for at least two milliseconds during each power
system cycle. It is also possible to add external tripping
criteria by binary signal.
The trip command from the differential protection including
sensitive differential protection and circuit breaker failure
backup-trip commands can be set either as self-resetting or
latched. In second case the manual reset is needed in order
to reset the individual bay trip output contacts.
Sensitive differential level BZISGGIO
Differential protection zones in REB670 include a sensitive
operational level. This sensitive operational level is designed
to be able to detect internal busbar earth faults in low
impedance earthed power systems (i.e. power systems where
the earth-fault current is limited to a certain level, typically
between 300A and 2000A primary by a neutral point reactor
or resistor). For increased security, the sensitive differential
protection must be externally enabled by a binary signal (e.g.
from external open delta VT overvoltage relay or external
power transformer neutral point overcurrent relay). Finally it is
as well possible to set a time delay before the trip signal from
the sensitive differential protection is given. This sensitive
level can be alternatively used in special applications when
high sensitivity is required from busbar differential protection
(i.e. energizing of dead bus via a long line).
Operation and operating characteristic of the sensitive
differential protection can be set independently from the
operating characteristic of the main differential protection.
However, the sensitive differential level is blocked as soon as
the total incoming current exceeds the pre-set level or when
differential current exceed the set minimum pickup current for
the usual differential protection. Therefore, by appropriate
settings it can be ensured that this sensitive level is blocked
for all external multi-phase faults, which can cause CT
saturation. Operating characteristic of sensitive differential
characteristics is shown in figure
1 .
Check zone
For busbar protection in double busbar stations when
dynamic zone selection is needed, it is sometimes required to
include the overall differential zone (that is, check zone).
Hence, the built-in, overall check zone is available in the IED.
Because the built-in check zone current measurement is not
dependent on the disconnector status, this feature ensures
stability of Busbar differential protection even for completely
wrong status indication from the busbar disconnectors. It is
to be noted that the overall check zone, only supervise the
usual differential protection operation. The external trip
commands, breaker failure backup-trip commands and
sensitive differential protection operation are not supervised
by the overall check zone.
The overall check zone has simple current operating
algorithm, which ensures check zone operation for all internal
faults regardless the fault current distribution. To achieve this,
the outgoing current from the overall check zone is used as
restraint quantity. If required, the check zone operation can
be activated externally by a binary signal.
Open CT detection
The innovative measuring algorithm provides stability for open
or short-circuited main CT secondary circuits, which means
that no separate check zone is actually necessary. Start
current level for open CT detection can usually be set to
detect the open circuit condition for the smallest CT. This
built-in feature allows the protection terminal to be set very
sensitive, even to a lower value than the maximum CT primary
rating in the station. At detection of problems in CT
secondary circuits, the differential protection can be instantly
blocked and an alarm is given. Alternatively, the differential
protection can be automatically desensitized in order to
ensure busbar differential protection stability during normal
through-load condition. When problems in CT secondary
circuits have been found and associated error has been
corrected a manual reset must be given to the IED. This can
be done locally from the local HMI, or remotely via binary
input or communication link.
However, it is to be noted that this feature can only be partly
utilized when the summation principle is in use.
Differential protection supervision
Dual monitoring of differential protection status is available.
The first monitoring feature operates after settable time delay
when differential current is higher than the user settable level.
This feature can be, for example, used to design automatic
reset logic for previously described open CT detection
feature. The second monitoring feature operates immediately
when the busbar through-going current is bigger than the
user settable level. Both of these monitoring features are
phase segregated and they give out binary signals, which can
be either used to trigger disturbance recorder or for alarming
purposes.
4. Zone selection
Typically CT secondary circuits from every bay in the station
are connected to the busbar protection. The built-in software
feature called “Zone Selection” gives a simple but efficient
control over the connected CTs to busbar protection IED in
order to provide fully operational differential protection
scheme for multi-zone applications on both small and large
buses.
The function consists of dedicated disconnector/circuit
breaker status monitoring algorithm, bay dedicated CT-
connection control algorithm and zone interconnection
algorithm.
Switch status monitoring
For stations with complex primary layout (that is, double
busbar single breaker station with or without transfer bus) the
information about busbar disconnector position in every bay
is crucial information for busbar protection. The positions of
Busbar protection REB670 1MRK505212-BEN E
Pre-configured
Product version: 1.2
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