ABB Relion 670 Series RES670, Technical Manual

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1. Current fundamental frequency component > IMinOpHarmBlk
2. Current second harmonic component > IMinOpHarmBlk
3. Ratio of the 2nd harmoinc component in relation to the fundamental frequency
component in the residual current exceeds the preset level defined parameter
2ndHarmStab setting
If all the above three conditions are fulfilled then ST2NDHRM function output signal is
set to logical value one and harmonic restraining feature to the function block is
applicable.
In addition to the basic functionality explained above the 2
nd
harmonic blocking can be set
in such way to seal-in until residual current disappears. This feature might be required to
stabilize EF4PTOC (51N67N) during switching of parallel transformers in the station. In
case of parallel transformers there is a risk of sympathetic inrush current. If one of the
transformers is in operation, and the parallel transformer is switched in, the asymmetric
inrush current of the switched in transformer will cause partial saturation of the
transformer already in service. This is called transferred saturation. The 2
nd
harmonic of
the inrush currents of the two transformers is in phase opposition. The summation of the
two currents thus gives a small 2
nd
harmonic current. The residual fundamental current is
however significant. The inrush current of the transformer in service before the parallel
transformer energizing, is a little delayed compared to the first transformer. Therefore we
have high 2
nd
harmonic current component initially. After a short period this current is
however small and the normal 2
nd
harmonic blocking resets. If the BlkParTransf function
is activated the 2
nd
harmonic restrain signal is latched as long as the residual current
measured by the relay is larger than a selected step current level by using setting
UseStartValue .
This feature has been called Block for Parallel Transformers. This 2
nd
harmonic seal-in
feature is activated when all of the following three conditions are simultaneously fulfilled:
1. Feature is enabled by entering setting parameter BlkParTransf = On .
2. Basic 2
nd
harmonic restraint feature has been active for at least 70ms.
3. Residual current magnitude is higher than the set pickup value for one of the four
residual overcurrent stages. By a parameter setting Use_PUValue it is possible to
select which one of the four pickup values that will be used ( Pickup1 or Pickup2 or
Pickup3 or Pickup4 ).
Once Block for Parallel Transformers is activated the basic 2
nd
harmonic blocking signal
is sealed-in until the residual current magnitude falls below a value defined by parameter
setting
Use_PUValue (see condition 3 above).
Simplified logic diagram for 2
nd
harmonic blocking feature is shown in figure 59 .
Section 8
1MRK 511 365-UUS A
Current protection
208 Phasor measurement unit RES670 2.1 ANSI
Technical manual