Switch Onto Fault Logic - ABB REC670 Applications Manual

Section 8
Current protection
8.4.3.4
174
residual fundamental 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
current initially. After a short period this current will however be small and the normal
nd
2 harmonic blocking will reset.
51N
Power System
ANSI05000136 V1 EN-US
Figure 68: Application for parallel transformer inrush current logic
If the BlkParTransf function is activated, the 2
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.

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.
51N
en05000136_ansi.vsd
nd
harmonic restrain signal will latch as
1MRK 511 401-UUS A
nd
harmonic
M15282-106 v4
Bay control REC670 2.2 ANSI
Application manual