ABB RELION REB670, Applications Manual

Page: 194 / 554

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.
7.2.3 Setting guidelines
SEMOD127939-1 v1
SEMOD127941-4 v3
A typical starting time delay of 24ms is subtracted from the set trip
time delay, so that the resulting trip time will take the internal IED start
time into consideration.
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).
Section 7
1MRK 505 370-UUS A
Current protection
188 Busbar protection REB670 2.2 ANSI
Application manual