Setting Guidelines - ABB REB670 Applications Manual

1MRK 505 337-UUS -
7.2.3
Application manual
In many applications several steps with different current pick up levels and time delays are
needed. PH4SPTOC(51) can have up to four different, individual settable, steps. The
flexibility of each step of PH4SPTOC(51) function is great. The following options are
possible:
Choice of delay time 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 all overcurrent IEDs, to be co-ordinated against each other,
should have the same time delay characteristic. Therefore a wide range of standardised
inverse time characteristics are available: IEC and ANSI. It is also possible to programme
a user defined inverse time characteristic.
Normally it is required that the phase overcurrent function shall reset as fast as possible
when the current level gets lower than the operation level. In some cases some sort of time
delayed reset is required. Therefore three different kinds of reset time 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 then
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 second harmonic content.
This can be used to avoid unwanted operation of the protection. Therefore the Four step
phase overcurrent protection (OC4PTOC, 51/67) function have a possibility of second
harmonic restrain if the level of this harmonic current reaches a value above a set
percentage of the fundamental current.

Setting guidelines

The parameters for the four step phase overcurrent protection function (OC) are set via the
local HMI or Protection and Control IED Manager (PCM 600).
The following settings can be done for the four step phase overcurrent protection.
Operation: Off/On
IBase: Base current in primary A. This current is used as reference for current setting. It
can be suitable to set this parameter to the rated primary current of the protected object.
Section 7
Current protection
175