Application; General Ied Application - ABB Relion 670 Series Applications Manual

1MRK 505 370-UUS Rev. K
Section 2
2.1

General IED 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 breaker-and-a-
half 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-ground faults in solidly grounded or low impedance
grounded power systems, as well as all internal multi-phase faults in isolated or high-impedance
grounded power systems.
Ordering of PT 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 PT inputs will
reduce number of available CT inputs (in total 24 analogue inputs are the product limit). Consequently
when PT 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 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 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 pickup. This sensitive operational
pickup is designed to be able to detect internal busbar ground faults in low impedance grounded power
systems (that is, power systems where the ground-fault current is limited to a certain level, typically
between 300A and 2000A primary by a neutral point reactor or resistor). Alternatively this sensitive
Busbar protection REB670
Application manual

Application

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Section 2
Application
SEMOD121007-5 v9
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