Woodward HighPROtec MCDLV4, Руководство пользователя, Страница: 631 / 1275

Protective Elements
For the secondary winding system:
Zero sequence removal will be calculated for the secondary winding system, if the W2con value is set to yn or zn.
A zero sequence current can only flow:
1. If the vector group is odd;
2. If the neutral is connected to ground; and
3. The grid on the secondary side is grounded as well
⃗
I
W2
' ' '
=⃗
I
W2
' '
−⃗
I
0, W2
' '
After setting the values for the percentage restrained characteristic curve, the settings for harmonic and transient
restraining have to be defined. Both the harmonic and transient restraining settings depend on many parameters:
•
Transformer type;
•
Transformer material;
•
Operational parameter of the grid; and
•
Time of energizing relative to the sinusoidal phase.
Therefore it is very difficult to give “
one for all” settings in this area and to find a compromise between making a
differential relay extremely fast and extremely reliable in its trip decisions.
Beginning with the static characteristic curve, typical slopes of 25% and 50% for both sections are recommended.
They will be obtained by the following settings:
Id(IS0)
Default (example)
0.3
Id(IS1)
Default (example)
1.0
Id(IS2)
Default (example)
4.0
In case of harmonic or transient restraint, the curve will be added by a static offset d(H,m)
To be able to withstand magnetizing inrush currents of typical values, the following value of d(H,m) = 8 is
recommended.
d(H,m)
Default (example)
8
In case that harmonic restraint threshold is reached, this value will be added to the characteristic curve.
It is important to estimate the necessary harmonic threshold to obtain stability against magnetizing inrush,
CT
saturation,
and over-excitation. The harmonics seen under different operational conditions like magnetizing inrush
and
CT saturation
depend on many different parameters.
631 MCDLV4 DOK-HB-MCDLV4-2E