Setting Guidelines - ABB REL650 Applications Manual

Section 7
Current protection
7.3.3
180
characteristics. The selectivity between different overcurrent protections is normally
enabled by co-ordination between the function time delays of the different protections. To
enable optimal co-ordination between all overcurrent protections, they should have the
same time delay characteristic. Therefore a wide range of standardized inverse time
characteristics are available: IEC and ANSI.
The time characteristic for step 1 and 4 can be chosen as definite time delay or inverse time
characteristic. Step 2 and 3 are always definite time delayed and are used in system where
IDMT is not needed.
Power transformers can have a large inrush current, when being energized. This
phenomenon is due to saturation of the transformer magnetic core during parts of the
period. There is a risk that inrush current will reach levels above the pick-up current of the
phase overcurrent protection. The inrush current has a large 2nd harmonic content. This
can be used to avoid unwanted operation of the protection. Therefore, OC4PTOC (51/67)
have a possibility of 2nd harmonic restrain if the level of this harmonic current reaches a
value above a set percentage of the fundamental current.

Setting guidelines

When inverse time overcurrent characteristic is selected, the operate time
of the stage will be the sum of the inverse time delay and the set definite
time delay. Thus, if only the inverse time delay is required, it is important
to set the definite time delay for that stage to zero.
The parameters for Four step phase overcurrent protection 3-phase output OC4PTOC
(51/67) are set via the local HMI or PCM600.
The following settings can be done for OC4PTOC (51/67).
GlobalBaseSel: Selects the global base value group used by the function to define (IBase),
(VBase) and (SBase).
MeasType: Selection of discrete Fourier filtered (DFT) or true RMS filtered (RMS)
signals. RMS is used when the harmonic contents are to be considered, for example in
applications with shunt capacitors.
Operation: The protection can be set to Disabled or Enabled
2ndHarmStab: Operate level of 2nd harmonic current restrain set in % of the fundamental
current. The setting range is 5 - 100% in steps of 1%. Default setting is 20%.
1MRK 506 334-UUS A
Application manual