Setting Guidelines - ABB REL650 Applications Manual

Section 7
Current protection
7.4.3
190
If VT inputs are not available or not connected, setting parameter
DirModeSelx (x=step 1, 2, 3 or 4) shall be left to default value,
Nondirectional, or set to Disabled.
In many applications several steps with different current pick up levels and time delays are
needed. OC4SPTOC (51_67) can have up to four different, individual settable, steps. The
flexibility of each step of the OC4SPTOC (51_67) function 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.
Power transformers can have a large inrush current, when being energized. This
phenomenon is due to the saturation of the transformer magnetic core during parts of the
period. There is a risk that inrush current will reach the levels above the pick-up current
of the phase overcurrent protection. The inrush current has a large second harmonic
content. This can be used to avoid the unwanted operation of the protection. Therefore,
OC4SPTOC (51/67) function has a possibility of a second harmonic restrain if the level
of this harmonic current reaches a value above a set percentage of the fundamental current.
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 functions is normally
enabled by co-ordination between the function time delays of the different functions. To
enable optimal co-ordination between all overcurrent functions, 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.

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.
1MRK 506 334-UUS A
Application manual