ABB RELION 670 Series Applications Manual page 152

Section 7
Current protection
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. It is also possible to
tailor make the inverse time characteristic.
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. In some cases some sort of delayed reset is
required. Therefore different kinds of reset characteristics can be used.
For some protection applications there can be a need to change the current pick-up level for some
time. A typical case is when the protection will measure the current to a large motor. At the start
up sequence of a motor the start current can be significantly larger than the rated current of the
motor. Therefore there is a possibility to give a setting of a multiplication factor to the current
pick-up level. This multiplication factor is activated from a binary input signal to the function.
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.
The phase overcurrent protection is often used as protection for two and three phase short
circuits. In some cases it is not wanted to detect single-phase ground faults by the phase
overcurrent protection. This fault type is detected and cleared after operation of ground fault
protection. Therefore it is possible to make a choice how many phases, at minimum, that have to
have current above the pick-up level, to enable operation. If set
current in one phase only. If set
7.1.3 Setting guidelines
The parameters for the directional phase overcurrent protection, four steps 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 Enabled or Disabled .
AngleRCA : Protection characteristic angle set in degrees. If the angle of the fault loop current has
the angle RCA, the direction to the fault is forward.
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2 of 3 or 3 of 3 single-phase ground faults are not detected.
When inverse time overcurrent characteristic is selected, the trip 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 505 337-UUS A
1 of 3 it is sufficient to have high
Application manual
IP14982-1 v1
M12982-4 v14