Chapter 2 – Twelve–Pulse Technology
II F2
2 - 10 DCS 600 Manual for 12 – Pulse Operation
2.5 Advanced current measurement
DC drives from ABB are equipped with DC current measurement by
AC current transformer. If such drives are connected to and used at
weak networks and if the current controller is tuned for fast time re-
sponse it may happen, that an interaction can be recognized bet-
ween the networks and the drive. The most critical configuration is
the 12-pulse parallel one in the range of 900A –5150A
(C3 and C4).
Sometimes it will appear as a current instability or increase of
bridge change over time and due to an remaining magnetizing in
the current transformer.
GAP IN THE CURRENT
FEEDBACK BUT NOT
IN THE REAL CURRENT
Figure 2/12
1%
3%
The current - zero signal is too short.
ACTUAL VALUE
OF THE DC CURRENT
t1
wrong feedback value due to
Imag
Figure 2/13
Graph of wrong actual current signal
To avoid this problem the converters (900A…5150A) can be equip-
ped with a current measurement aid (CMA2) as an option.
The board is located outside the converter module quite near the
current transformer.
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