Setting Guidelines - ABB REQ650 Applications Manual

1MRK 505 291-UEN A
6.3.3
Application manual
If VT inputs are not available or not connected, setting parameter
DirModex (x = step 1, 2, 3 or 4) shall be left to default value Non-
directionalor set to Off.
In many applications several steps with different current pick up levels and time
delays are needed. OC4PTOC can have up to four different, individual settable, steps.
The flexibility of each step of OC4PTOC is great. The following options are possible:
Non-directional / Directional function: In most applications the non-directional
functionality is used. This is mostly the case when no fault current can be fed from the
protected object itself. In order to achieve both selectivity and fast fault clearance, the
directional function can be necessary.
Choice of delay time characteristics: There are several types of delay time
characteristics available such as definite time delay and different types of inverse time
delay 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 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
are set via the local HMI or PCM600.
The following settings can be done for OC4PTOC.
GlobalBaseSel: Selects the global base value group used by the function to define
(IBase), (UBase) and (SBase).
Section 6
Current protection
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