Zone Selection - ABB Relion 670 Series Product Manual

Busbar protection REB670
Version 2.2
by a binary signal (e.g. start signal 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 stations with double or triple
busbars 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 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
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circuits have been found and associated error has been
corrected a manual reset must be given to the IED. This can
be done from the local HMI via the 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.
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Figure 11.

5. 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.
Switch status monitoring
For stations with complex primary layout the information
about busbar disconnector position in every bay is crucial
information for busbar protection. The positions of these
disconnectors then actually determine which CT input (that
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is, bay) is connected to which differential protection zone.
For some more advanced features like end-fault or blind-
spot protection the actual status of the circuit breaker in
some or even all bays can be vital information for busbar
protection as well. The switch function block is used to take
the status of two auxiliary contacts from the primary device,
evaluate them and then to deliver the device primary
contact position to the rest of the zone selection logic.
For such applications typically two auxiliary contacts (that
is, normally open and normally closed auxiliary contacts)
from each relevant primary switching object shall be
connected to the IED. Then the status for every individual
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Simplified logic for Zone supervision features
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