ABB ACS880-77CC, Hardware Manual

Page: 51 / 128

• du/dt filter protects generator insulation system and reduces bearing currents
• common mode filter mainly reduces bearing currents (option).
To avoid damage to generator bearings, the cables must be selected and installed according
to the instructions given in this manual. In addition, insulated N-end (non-converter end)
bearings must be used.
Selecting the power cables
￭
General rules
Dimension the grid cable or busbar and generator cable according to local regulations :
• The cable must be able to carry the converter load current. See the technical data for
the rated currents.
• The cable must be rated for at least 90 °C (194 °F) maximum permissible temperature
of conductor in continuous use. See also section
Additional US and Canada
requirements (page 54) .
• The inductance and impedance of the PE conductor/cable (grounding wire) must be
rated according to permissible touch voltage appearing under fault conditions (so that
the fault point voltage will not rise excessively when a ground fault occurs).
• The rated voltage between the conductors of the cable should be minimum 1 kV.
For generators, the symmetrical shielded generator cable is highly recommended. See
section
Alternative power cable types (page 53) .
Note: When continuous conduit is employed, shielded cable is not required.
Note: When using a four-conductor system, consult the generator manufacturer regarding
bearing and disturbance shielding.
In a non-symmetrical four-conductor system, voltage can be induced to the separate PE
conductor, which rises generator frame potential and causes current to ground through the
generator bearings and shaft. This causes extra wear. Whereas, in a symmetrical shielded
cable, the high capacitance between the PE conductor and the phase conductors forms an
LC filter reducing bearing currents and voltage changes.
A four-conductor system is allowed for grid cabling, but shielded symmetrical cable is highly
recommended.
￭
Sufficient conductivity of the protective conductor
The protective conductor must always have an adequate conductivity.
Unless local wiring regulations state otherwise, the cross-sectional area of the protective
conductor must agree with the conditions that require automatic disconnection of the supply
required in 411.3.2. of IEC 60364-4-41:2005 and be capable of withstanding the prospective
fault current during the disconnection time of the protective device.
The cross-sectional area of the protective conductor can either be selected from the table
below or calculated according to 543.1 of IEC 60364-5-54.
This table shows the minimum cross-sectional area related to the phase conductor size
according to IEC 61800-5-1 when the phase conductor and the protective conductor are
made of the same metal. If this is not so, the cross-sectional area of the protective earthing
Planning the electrical installation 51