ABB DCS 400, Руководство пользователя

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II K 5-10
Installation
11 Screening
12 Signal cables
The cables for digital signals, which are longer than 3 m and all ca-
bles for analogue signals, must be screened. Each screen must be
connected at
both ends by metal clamps (see figure 5.2-4) or
comparable means directly on clean metal surfaces, if both
earthing points belong to the same earth line. Otherwise a capaci-
tor must be connected to earth on one end. In the converter cubicle
this kind of connection must be made directly on the sheet metal
close to the terminals (see
27 ) and if the cable comes from outside
also on the PE bar (see 25 and 26 ). At the other end of the cable
the screen must be well connected with the housing of the signal
emitter or receiver.
Figure 5.2 - 4 Connection of a cable screen with the aid of metal
clamp to the metal surface
13
Power cables
with screens
Power cables with screens are necessary, if they run over long
distances (>20 m) where they are susceptible to EMC environ-
mental conditions. The cable may have e.g. either a braided or spi-
ral screen made preferably of copper or aluminium. The transfer
impedance Z
T
of the power cable must be less than 0.1
Ω
/m in the
frequency range up to 100 MHz, in order to ensure an effective re-
duction of emission and a significant increase of immunity. The
screen must be pressed by a well conducting metal clamp directly
against the mounting plate or the PE bar of the converter cubicle
(see
24 ). Another connection option is via EMC sleeve. There the
contact surface shall be clean and as large as possible. The PE
wire can be connected with a normal cable socket at the PE bar.
Screened cables to the armature and to the excitation winding
cause the lowest noise level.