Danfoss VLT AQUA FC 202 - Bearing Currents

•
•
•
•
Standard IEC line motors (IEC 60034-30-1)
The standard IEC 60034-30-1 of March 2014 replaces the standard 60034-30:2008, which has dened 3 eciency levels for 3-phase
induction motors. The updated standard IEC 60034-30-1 now includes the 4
th
eciency level, IE4. Furthermore, 8-pole motors and
an extended power range are now included in the standard.
Eciency classes:
In the IEC 60034-30-1, the following eciency classes are dened for induction motors:
IE1 (Standard eciency).
IE2 (High ecienc y).
IE3 (Premium eciency).
IE4 (Super premium eciency).
IE = Internation eciency.
These motor types can all be operated with Danfoss VLT® drives.
More information on this topic can be found in the publication Motor Technologies for Higher Eciency in Applications. This docu-
ment can be downloaded from www.danfoss.com.
5.1.3 Bearing Currents
Protecting the motor insulation and bearings
The drive employs modern IGBT inverter technology. Regardless of the frequency, the drive output comprises pulses of approxi-
mately the drive DC bus voltage with a very short rise time. The pulse voltage can almost double at the motor terminals, depending
on the attenuation and reection properties of the motor cable and the terminals. This can cause extra stress on the motor and
motor cable insulation. Modern AC drives with their fast-rising voltage pulses and high-switching frequencies can generate current
pulses that ow through the motor bearings. Gradually, these current pulses can erode the bearing races and rolling elements. Op-
tional dU/dt lters protect the motor insulation system and reduce bearing currents. Optional common-mode lters mainly reduce
bearing currents. Insulated N-end (non-drive end) bearings protect the motor bearings.
Practical tips
Usually, the shielding surface of the motor cable is connected to the frame of the terminal box and not to the motor stator frame.
However, the motor terminal box on some motors can be mounted to the stator housing with a considerable change of the high-
frequency currents and impedance. Typically, there is a gasket between the terminal box and the stator frame, and the box is attach-
ed to the motor frame with 4 small screws. Conducted measurements on these motors showed that screws did not provide a low
impedance from the terminal box to the stator and therefore, the common-mode currents were oscillated with a noticeable magni-
tude.
Applying high-frequency bonding straps between the motor terminal box and the stator frame helps providing low impedance for
high-frequency currents and therefore eliminating the common-mode current oscillations in the installation.
e30bh117.10
Illustration 17: Installation of EMC straps from the Terminal Box to the Motor Frame
Sometimes, so called NYCWY cables are used to connect the motor to the drive inverter. The symmetry of the PE conductor in these
cables is achieved by a conductor surrounding all the phase leads. These cables, however, prevent common-mode currents at the
fundamental frequency only.
AJ300847815559en-000101 / 130R033732 | Danfoss A/S © 2020.09
Product Overview
VLT® AQUA Drive FC 202
Design Guide