Seg HighTECH MRU3-2, Руководство пользователя

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TB MRU3-2 12.00 E 11
4.4.4 Negative sequence system of
a symmetrical voltage system
Figure 4.3: Graphical determination of the negative sequence system in a symmetrical system
Figure 4.3 shows a symmetrical vector system. As in-
dicated in the calculation the
MRU3-2 forms the nega-
tive sequence system. For this it rotates per software
both voltage vectors U
2
by 240
o
and U
3
by 120
o
and adds them. Acc. to definition the result of the vec-
tor must be multiplied by 1/3. In this example the sum
equals zero. Conclusion: the source system is symmet-
rical.
4.4.5 System with voltage unbalance
Figure 4.4: Graphical determination of the negative sequence system in an asymmetrical system
Figure 4.4 shows the voltage vectors of an asymmetri-
cal grid. A residual negative sequence system voltage,
which is not zero, is calculated in this example. Should
this residual voltage exceed the set treshold, which is
indicated as rms value, the relay trips after the prese-
lected time delay.
For the exact rotation of the current vectors by 120
o
or
240
o
the system frequency has to be pricisely ad-
justed.