Application - ABB Relion 670 Series Product Manual

Busbar protection REB670
Version 2.2

2. Application

The Intelligent Electronic Device (IED) is designed for the
selective, reliable and fast differential protection of busbars,
T-connections and meshed corners in up to 6 zones. It can
be used for protection of single, double and triple busbar
with or without transfer bus, double circuit breaker or one-
and-half circuit breaker stations. The IED is applicable for
the protection of medium voltage (MV), high voltage (HV)
and extra high voltage (EHV) installations at a power
system frequency of 50Hz or 60Hz. It can detect all types of
internal phase-to-phase and phase-to-earth faults in solidly
earthed or low impedance earthed power systems, as well
as all internal multi-phase faults in isolated or high-
impedance earthed power systems.
Ordering of VT inputs inside of the busbar protection IED
will allow integration of voltage related functionality like
under-voltage release, residual over-voltage, power
functions, metering and voltage recording during the faults.
However attention shall be given to the fact that inclusion of
VT inputs will reduce number of available CT inputs (in total
24 analogue inputs are the product limit). Consequently
when VT inputs are ordered the busbar protection IED will
be applicable for buses with a fewer number of bays.
Practically the number of available CT inputs will limit the
size of the station which can be protected.
The IED has very low requirements on the main current
transformers (that is, CTs) and no interposing current
transformers are necessary. For all applications, it is
possible to include and mix main CTs with 1A and 5A rated
secondary current within the same protection zone.
Typically, CTs with up to 10:1 ratio difference can be used
within the same differential protection zone. Adjustment for
different main CT ratios is achieved numerically by a
parameter setting.
The numerical, low-impedance differential protection
function is designed for fast and selective protection for
faults within protected zone. All connected CT inputs are
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provided with a restraint feature. The minimum pick-up
value for the differential current is set to give a suitable
sensitivity for all internal faults. The pick-up setting for the
SEMOD121007-5 v9
fault current must be less than 80% of the lowest fault
current that can occur on the protected bus bars. If the
minimum fault current is high enough, the set value should
be set higher than the maximum load current. This setting is
made directly in primary amperes. The operating slope for
the differential operating characteristic is fixed to 53% in the
algorithm.
The fast tripping time (minimum trip time is 5ms when SOM
output module is used) of the low-impedance differential
protection function is especially advantageous for power
system networks with high fault levels or where fast fault
clearance is required for power system stability.
All CT inputs are provided with a restraint feature. The
operation is based on the well-proven RADSS percentage
restraint stabilization principle, with an extra stabilization
feature to stabilize for very heavy CT saturation. Stability for
external faults is guaranteed if a CT is not saturated for at
least two milliseconds during each power system cycle.
The advanced open CT detection algorithm detects instantly
the open CT secondary circuits and prevents differential
protection operation without any need for additional check
zone.
Differential protection zones in the IED 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 (that is, 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). Alternatively this sensitive
level can be used when high sensitivity is required from
busbar differential protection (that is, energizing of the bus
via long line).
Overall operating characteristic of the differential function in
the IED is shown in figure 1.
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