Switch Onto Fault Logic - ABB RELION 670 Series Applications Manual

1MRK 504 152-UEN B
of the two transformers will be in phase opposition. The summation of the two currents will
thus give a small 2
significant. The inrush current of the transformer in service before the parallel transformer
energizing, will be a little delayed compared to the first transformer. Therefore we will have
nd
high 2
the normal 2
Power System
IEC05000136 V1 EN-US
Figure 253: Application for parallel transformer inrush current logic
If the BlkParTransf function is activated the 2
the residual current measured by the relay is larger than a selected step current level. Assume
that step 4 is chosen to be the most sensitive step of the four step residual overcurrent
protection function EF4PTOC. The harmonic restrain blocking is enabled for this step. Also the
same current setting as this step is chosen for the blocking at parallel transformer energizing.
Below the settings for the parallel transformer logic are described.
UseStartValue : Gives which current level that should be used for activation of the blocking
signal. This is given as one of the settings of the steps: Step 1/2/3/4. Normally the step having
the lowest operation current level should be set.
BlkParTransf : This parameter can be set Off / On , the parallel transformer logic.
8.4.3.5

Switch onto fault logic

In case of energizing a faulty object there is a risk of having a long fault clearance time, if the
fault current is too small to give fast operation of the protection. The switch on to fault
function can be activated from auxiliary signals from the circuit breaker, either the close
command or the open/close position (change of position).
This logic can be used to issue fast trip if one breaker pole does not close properly at a manual
or automatic closing.
SOTF and Under Time are similar functions to achieve fast clearance at asymmetrical closing
based on requirements from different utilities.
The function is divided into two parts. The SOTF function will give operation from step 2 or 3
during a set time after change in the position of the circuit breaker. The SOTF function has a
set time delay. The Under Time function, which has 2
operation from step 4. The 2nd harmonic restrain will prevent unwanted function in case of
transformer inrush current. The Under Time function has a set time delay.
Below the settings for switch on to fault logics are described.
SOTF operation mode : This parameter can be set: Off/SOTF/Under Time/SOTF+Under Time .
Application manual
nd
harmonic current. The residual fundamental current will however be
harmonic current initially. After a short period this current will however be small and
nd
harmonic blocking will reset.
IN>
IN>
en05000136.vsd
nd
harmonic restrain signal will latch as long as
nd
harmonic restrain blocking, will give
Section 8
Current protection
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