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

1MRK 505 337-UUS A
Section 2
2.1

General IED application

The IED is designed for the selective, reliable and fast differential protection of busbars, T-
connections and meshed corners. It can be used for protection of single and double 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 (shortest trip time is 5ms) 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
Application manual

Application

Section 2
Application
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