31
Motor
Manual
garding high frequency currents.
• Effectiveness of protection to enhance electromagnetic
compatibility (EMC)
• EMC screened equipment suitable for VFD opera-
tion is recommended and could, among others,
include:
• Sufficient cable screening, cable gland connec-
tions, suitable high frequency earthing etc.
To reduce the risk of bearing currents and corresponding
downtime of the motor application, please see the sugges-
tions for motor applications operated with VFD’s in the
section 8.5 Hoyer VFD application suggestions.
8.4 Additional solutions for limitation of bear-
ing currents
In special cases where bearing current still occurs, or for
essential applications where optimised uptime is signifi-
cant, additional actions may be recommended. Depending
on application and installation requirements, the follow-
ing advanced solution will ensure a high reliability:
• Grounding brushes can be mounted to ensure a good
earthing connection between motor housing and shaft.
• Insulated bearing in NDE and DE
• Hybrid bearing with ceramic balls in NDE or DE.
• Combination of Hybrid bearing in NDE and brush in DE
Grounding brushes are installed outside the motor hous-
ing and makes the connection from stator to shaft. Brush-
es must periodically be inspected for wear and tear in or-
der to ensure an optimized protection.
With insulated bearings mounted in drive-end and none-
drive-end, the shaft is electrically insulated from the sta-
tor, meaning that no bearing current will run from stator
to rotor. Bearings with ceramic balls are recommended as
the most reliable solution.
Be aware of any bearings in the application, so that the
bearing current does not pass through these when the mo-
tor bearings are insulated and a grounding brush is not
used.
8.5 Hoyer VFD application suggestions
To ensure a reliable VFD- and motor operation, please
take the suggestions listed in below table into account.
In general Hoyer recommends reenforced insolation sys-
tems and insulated bearings in NDE when the motor has
a power-size above 75 kW or a supply voltage above 500 V.
Common mode filters are recommended above 75 kW and
dU/dt filters should be implemented when supply voltages
surpasses 500 V. Hoyer can deliver all types of filters upon
request.
Supply
voltage
Power
Winding
insula-
tion
Motor
bearings
Drive
filters*
< 500 V
< 75 kW
Hoyer
standard
insulation
Standard
bearings
No filter
needed
≥ 75 kW
Hoyer
standard
insulation
Insulated
non-drive
end bear-
ing
Common
mode filter
≥ 500 V
<75 kW
Hoyer
reinforced
insulation
Standard
bearings
dU/dt filter
≥ 75 kW
Insulated
non-drive
end bear-
ing
dU/dt filter
& common
mode filter
*Common mode filters can generally be recommended in all mo-
tor sizes
Hoyer premium reinforced insulation system can be implemented
upon request
Table 14: Hoyer motor recommendations to bearing current and
filter mitigation with VFD control.
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