Switch Onto Fault Logic - Hitachi Relion 670 Series Applications Manual

Section 8
Current protection
saturation. The 2
The summation of the two currents will thus give a small 2
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
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high 2
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2 harmonic blocking will reset.
Power System
ANSI05000136 V1 EN-US
Figure 59:
If the BlkParTransf function is activated, the 2
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: 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.
8.2.3.4

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.
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
harmonic restrain will prevent unwanted operation 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.
122
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harmonic of the inrush currents of the two transformers will be in phase opposition.
harmonic current initially. After a short period this current will however be small and the normal
51N 51N
Application for parallel transformer inrush current logic
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en05000136_ansi.vsd
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harmonic restrain signal will latch as long as the residual
harmonic restrain blocking, will give operation from step 4. The 2
1MRK511407-UUS Rev. N
harmonic current. The residual fundamental
Phasor measurement unit RES670
M15282-106 v6
nd
Application manual