4.6.4 Motor Bearing Currents
Motors with a rating 110 kW or higher combined with
adjustable frequency drives are best with NDE (Non-Drive
End) insulated bearings to eliminate circulating bearing
currents caused by motor size. To minimize DE (Drive End)
bearing and shaft currents, proper grounding is required
for:
•
Adjustable frequency drive
•
Motor
•
Motor-driven machine
•
Motor to the driven machine
Although failure due to bearing currents is infrequent, use
the following strategies to reduce the likelihood:
•
Use an insulated bearing
•
Apply rigorous installation procedures
•
Ensure that the motor and load motor are aligned
•
Strictly follow the EMC Installation guideline
•
Reinforce the PE so the high frequency
impedance is lower in the PE than the input
power leads.
•
Provide a good high frequency connection
between the motor and the adjustable frequency
drive
•
Ensure that the impedance from adjustable
frequency drive to building ground is lower than
the grounding impedance of the machine. Make
a direct ground connection between the motor
and load motor.
•
Apply conductive lubrication
•
Try to ensure that the line voltage is balanced to
ground.
•
Use an insulated bearing as recommended by the
motor manufacturer (note: motors from reputable
manufacturers typically have insulated bearings
as standard in motors of this size).
If found to be necessary and after consultation with
Danfoss:
•
Lower the IGBT switching frequency
•
Modify the inverter waveform, 60° AVM vs. SFAVM
•
Install a shaft grounding system or use an
isolating coupling between motor and load
•
Use minimum speed settings, if possible.
•
Use a dU/dt or sinus filter
4.7 AC Mains Connection
4.7.1 AC line input connections
Line power must be connected to terminals 91, 92 and 93
on the far left of the unit. Ground is connected to the
terminal on the right of terminal 93.
Terminal No.
Function
91, 92, 93
94
Line power R/L1, S/L2, T/L3
Ground
Table 4.5 Terminal Functions
Ensure that the power supply can supply the necessary
current to the adjustable frequency drive.
If the unit is without built-in fuses, ensure that the
appropriate fuses have the correct current rating.
4.7.2 External Fan Supply
If the adjustable frequency drive is supplied by DC or the
fan must run independently of the power supply, use an
external power supply. Make the connection on the power
card.
Terminal No.
Function
100, 101
102, 103
Auxiliary supply S, T
Internal supply S, T
Table 4.6 Terminal Functions
The connector on the power card provides the connection
of line voltage for the cooling fans. The fans are connected
from the factory to be supplied from a common AC line
(jumpers between 100–102 and 101–103). If external
power supply is needed, remove the jumpers and connect
the supply to terminals 100 and 101. Protect with a 5 A. In
UL applications, use a Littelfuse KLK-5 or equivalent.
Electrical Installation
VLT
®
AutomationDrive FC 302 Low Harmonic Drive
132–630 kW
40
Danfoss A/S © Rev. 04/2015 All rights reserved.
MG37A322
4
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