ABB Relion 670 series - Switch Onto Fault Logic

current will however be 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 high 2
nd
harmonic current initially. After a short
period this current will however be small and the normal 2
nd
harmonic blocking will reset.
en05000136_ansi.vsd
Power System
51N
51N
ANSI05000136 V1 EN
Figure 264: Application for parallel transformer inrush current logic
If the BlkParTransf function is activated, the 2
nd
harmonic restrain signal will latch as long
as 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 (51N_67N). 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.
The settings for the parallel transformer logic are described below.
BlkParTransf: This is used to Enable blocking at energising of parallel transformers.
Use_PUValue: Gives which current level should be used for the 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.
9.4.3.4 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 a 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.
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 513
Application manual