Application - ABB Relion 670 Series Product Manual

Busbar protection REB670
Customized
Product version: 1.2

1. Application

REB670 is designed for the selective, reliable and fast
differential protection of busbars, T-connections and meshed
corners. REB670 can be used for protection of single and
double 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. The IED 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.
REB670 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.
ABB
The numerical, low-impedance differential protection function
is designed for fast and selective protection for faults within
protected zone. All connected CT inputs are 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. For busbar protection applications typical
setting value for the minimum differential operating current is
from 50% to 150% of the biggest CT. 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 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.
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 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 (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
REB670 is shown in figure 1.
1MRK505273-BEN D
Issued: February 2015
Revision: D
3