Setting Guidelines - ABB RER670 Applications Manual

1MRK 506 375-UEN A
8.2.3
Railway application RER670 2.2 IEC
Application manual
• Short circuit protection of feeders.
• Back-up short circuit protection of transmission lines.
• Back-up short circuit protection of power transformers.
In many applications several steps with different current pickup levels and time
delays are needed. D2PTOC can have one or two, individually settable steps. 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.
If VT inputs are not available or not connected, the setting
parameter DirModex (x = step 1, 2) shall be left to the default value
Non-directional.
Choice of time delay characteristics: There are several types of time delay
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, several
inverse time characteristics are available within D2PTOC function.
Normally, it is required that the phase overcurrent protection shall reset as fast as
possible when the current level gets lower than the operation level.
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 2
harmonic content. This can be used to avoid unwanted operation of the protection
function. Therefore, D2PTOC has a possibility of 2
nd
of 2 harmonic component reaches a value above a set percent of the fundamental
frequency 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.
Section 8
Current protection
nd
harmonic restrain if the level
nd
IP14982-1 v1
M12982-4 v13
161