ABB DCS550 Series, Manual

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Electrical installation
3ADW000379R0501 DCS550 Manual e e
Installation components
①
Line reactors (L1)
When thyristor power converters operate, the line voltage is short-circuited during commutation from one
thyristor to the next. This operation causes voltage dips in the mains PCC (point of common coupling). For the
connection of a power converter system to the mains, one of the following configurations applies:
Configuration A
When using the power converter, a minimum of impedance is required to ensure proper
performance of the snubber circuit. Use a line reactor to meet this minimum impedance
requirement. The value must therefore not drop below 1 % u
k
(relative impedance voltage). It
should not exceed 10 % u
k
, due to considerable voltage drops at the converter outputs.
Configuration B
If special requirements have to be met at the PCC (standards like EN 61 800-3, DC and AC
drives at the same line, etc), different criteria must be applied for selecting a line reactor. These
requirements are often defined as a voltage dip in percent of the nominal supply voltage. The
combined impedance of Z
Line
and Z
L1
constitute the total series impedance of the installation. The
ratio between the line impedance and the line reactor impedance determines the voltage dip at
the connecting point. In such cases, line chokes with an impedance around 4 % are often used.
Example calculation with u
k
Line = 1 % and u
k
L
1
= 4 %:
Voltage dip = Z
Line
/ (Z
Line
+ Z
L1
) = 20 %. Detailed calculations see Technical Guide.
Configuration C
If an isolation transformer is used, it is possible to comply with certain connecting conditions per
Configuration B without using an additional line reactor. The condition described in Configuration
A will then likewise be satisfied, since the u
k
is > 1 %.
Configuration C1
When supplying 2 or more converters by one transformer use configuration A or B. One can see
that each drive needs its own line reactor.
Configuration D
In the case of high power converters, frequently a transformer is used for voltage matching.
When using an autotransformer for this purpose, additionally install a commutating reactor,
because the u
k
of commonly used autotransformers is too small.