Siemens SINAMICS G130 Engineering Manual page 248

EMC Installation Guideline
Engineering Information
2)
When several three-phase motor cables have to be routed in parallel between the converter and the associated
motor, it has to be ensured that all three phases of the three-phase system are routed within each motor cable. This
minimizes the magnetic leakage fields. The illustration below uses an example of three shielded, three-phase motor
cables routed in parallel.
3)
When DC cables (DC link cables or connection cables between Braking Modules and the associated braking
resistors) are routed, the feed and return lines must be routed in parallel with as little space between them as
possible to minimize magnetic leakage fields.
Information about using single-wire cables between the converter and the motor:
The use of 3-wire three-phase cables in the most symmetrical possible arrangement is recommended for the
connection between the converter and motor owing to the components at pulse frequency in the motor current. Also
recommended is the use of shielded cables, particularly in cases where it has not been possible to fully implement
other EMC measures. The reasons behind this recommendation are as follows:
With symmetrical 3-wire three-phase cables, the magnetic fields of the three wires almost entirely cancel each other
out within the cable which means that the resultant magnetic field at the surface of the cable sheath is virtually zero.
This means that cables of this kind can be safely installed in conductive metal cable ducts or on conductive metal
cable racks without the risk that currents of any significant magnitude are induced in the metallic connections. The
cables can also be safely inserted into the metal terminal boxes of the motors because no significant currents are
induced in the area around the cable entry point which might cause an inadmissibly high temperature rise in the
terminal box.
The conditions associated with single-wire cables are considerably less favorable. When the three wires of the three-
phase system are incorrectly bundled, the magnetic fields hardly cancel each other out at all and, even when the
wires are correctly bundled, the mutual compensation between magnetic fields is still less effective than with
symmetrical 3-wire three-phase cables. For this reason, the use of single-wire cables between the converter and
motor should be avoided wherever possible.
With very large cable cross sections (e.g. 150 mm
single-wire cables must often be used in order to ensure compliance with the specified bending radii. If the use of
single-wire cables is unavoidable for applications of this type, then it is absolutely essential to take note of the
following points:
·
The three wires of the three-phase system must be bundled as well as possible according to the description
in the section above in order to minimize the resultant magnetic field at the surface of the bundled wires.
·
The cable entry at the motor must be amagnetic in order to minimize the currents induced in the area
around the cable entry and thus also the temperature rise associated with induced currents. For some motor
series that are equipped as standard with magnetic terminal boxes or cable entries, such as SIMOTICS TN
series N-compact, amagnetic cable entries can be ordered as an option.
·
When shielded single-wire cables are used, the motor cable length should not exceed 15 to 20 m. With
motor cable lengths > 20 m, the cable shields should be connected only at the converter end (not at the
motor end) in order to prevent circulating currents in the shields which can cause an inadmissible
temperature rise in the cables.
·
If the cable shields are not connected at the motor end because the motor cables are > 20 m in length, a
cable suitable for high-frequency currents must be installed as a high-frequency bonding connection
between the converter and the motor housing in order to minimize bearing currents in the motor.
Since magnetic leakage fields will be higher by comparison with 3-wire three-phase cables and the shield cannot be
connected at the motor end when long motor cables are used, it must be expected that the drive will emit a higher
level of electromagnetic interference.
SINAMICS Engineering Manual – November 2015
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Ó Siemens AG
2
and AWG 300 MCM or larger) or with trailing cable arrangements,