10 Motor
10.1 Motor Cables
See
chapter 6.10 Cable Specifications
for more information
on wire type and sizes.
Voltage rating
Peak voltages up to 2.8 times the mains voltage of the
VLT
®
Parallel Drive Modules drive system can occur in the
motor cable. High peak voltages can severely stress the
motor cable. Use motor cables with rated voltage specifi-
cation of at least 0.6/1 kV. Cables in this range provide
good resistance to insulation breakdown.
Dimensions
Follow local codes for current capacity data for cables and
conductors. Widely used codes include: NFPA 70, EN
60204-1, VDE 0113-1, and VDE 0298-4. Overdimensioning
for harmonics is not required.
Length
Keep cables as short as possible. Voltage drop and heat
dissipation depends on the frequency and are proportional
to cable length. Consult the cable manufacturer specifi-
cations regarding the length and expected voltage drop
when connected to the drive system. See
chapter 6.10 Cable Specifications
.
NOTICE
CABLE LENGTH
With a standard VLT
®
Parallel Drive Modules drive
system, shielded cables up to 150 m (492 ft) long or
unshielded up to 300 m (984 ft) long provide full voltage
at the motor. If this cable length is exceeded, use a sine-
wave filter. For information on the selection of a sine-
wave filter, refer to the
VLT
®
FC-Series Output Filter Design
Guide
.
Shielding
See
chapter 9.5 EMC Recommendations
for information on
effective shielding.
NOTICE
TWISTED SHIELD ENDS (PIGTAILS)
Twisted shield ends increase the shield impedance at
higher frequencies, which reduces the shield effect and
increases the leakage current. To avoid twisted shield
ends, use integrated shield clamps. Refer to
.
1
2
130BE747.10
PE
PE
PE
PE
1 Correct grounding of shielded ends
2 Incorrect grounding using twisted shield ends (pigtail)
Illustration 10.1 Example of Shield Ends
10.2 Motor Coil Insulation
For motor cable lengths that are less than or equal to the
maximum cable length listed in
, use the motor insulation ratings shown in
. If a motor has lower insulation rating, Danfoss
recommends using a dU/dt or sine-wave filter.
Nominal mains voltage
Motor insulation
U
N
≤
420 V
Standard U
LL
=1300 V
420 V<U
N
≤ 500 V
Reinforced U
LL
=1600 V
500 V<U
N
≤ 600 V
Reinforced U
LL
=1800 V
600 V<U
N
≤ 690 V
Reinforced U
LL
=2000 V
Table 10.1 Motor Insulation Ratings
10.3 Motor Bearing Currents
To eliminate circulating bearing currents in all motors
installed with VLT
®
VLT
®
AutomationDrive FC 302 90 kW or
higher power frequency converters, install NDE (non-drive
end) insulated bearings. To minimize DE (drive end)
bearing and shaft currents, ensure proper grounding of the
frequency converter, motor, driven machine, and motor to
the driven machine.
Here are some standard mitigation strategies:
•
Use an insulated bearing.
•
Follow proper installation procedures.
-
Ensure that the motor and load motor
are aligned.
-
Follow the EMC Installation guideline.
-
Reinforce the PE so the high frequency
impedance is lower in the PE than the
input power leads.
Motor
Design Guide
MG37N102
Danfoss A/S © 6/2016 All rights reserved.
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