Protections Functions - ABB RET615 Product Manual

ABB
Transformer Protection and Control
RET615
Product version: 4.0

3. Protections functions

The IED features, three-phase, multi-slope
stabilized (biased) stage transformer differential
protection and an instantaneous stage to provide
fast and selective protection for phase-to-phase
short-circuit, winding interturn fault and bushing
flash-over protection. Besides second harmonic
restraint an advanced waveform-based blocking
algorithm ensures stability at transformer
energization and a fifth harmonic restraint function
ensures good protection stability at moderate
overexcitation of power transformers. Sensitive
restricted earth-fault protection (REF) completes
the overall differential protection providing
detection of even single phase-to-earth faults
close to the neutral earthing point of the
transformer. Either the conventional high-
impedance scheme or a numerical low-
impedance scheme can be selected for
protection of the transformer windings. When low-
impedance REF protection is used neither
stabilizing resistors nor varistors are needed and
as a further benefit the transforming ratio of the
neutral earthing CTs can differ from those of the
phase current transformers. Due to its unit
protection character and absolute selectivity REF
does not need to be time-graded with other
protection schemes, and therefore high-speed
fault clearance can be achieved.
The IED also incorporates a thermal overload
protection function, which supervises the thermal
stress of the transformer windings to prevent
premature aging of the insulation of the windings.
Multiple stages of short-circuit, phase-
overcurrent, negative-phase-sequence and earth-
fault back-up protection are separately available
for both sides of the power transformer. Earth-
fault protection based on the measured or
calculated residual voltage is also available.
Depending on the chosen standard configuration
the IED also features three-phase overvoltage
protection, three-phase undervoltage protection
and residual overvoltage protection. Further, the
IED also offers circuit-breaker failure protection.
Enhanced with optional hardware and software,
the IED also features three light detection
channels for arc fault protection of the circuit
breaker, busbar and cable compartment of metal-
enclosed indoor switchgear.
The arc-fault protection sensor interface is
available on the optional communication module.
Fast tripping increases staff safety and security
and limits material damage in an arc fault situation.
1MRS756891 F
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