Fuses; Motor Insulation; Motor Bearing Currents; Control Cable Routing - Danfoss VLT Series Installation Manual

Electrical Installation

4.4 Fuses

4.4.1 Motor Insulation

For motor cable lengths ≤ the maximum cable length
listed in chapter 5 Specifications, the recommended motor
insulation ratings are in Table 4.1. The peak voltage can be
up to twice the DC-link voltage, 2.8 times the mains
voltage, due to transmission line effects in the motor cable.
4 4
If a motor has a lower insulation rating, use a dU/dt or sine
wave filter.
Nominal mains voltage
≤420 V
U
N
420 V <U ≤500 V
N
500 V <U ≤600 V
N
600 V <U ≤690 V
N
Table 4.1 Motor Insulation at Various Nominal Mains Voltages

4.4.2 Motor Bearing Currents

All motors installed with FC 302 90 kW or higher power
frequency converters should have NDE (non-drive end)
insulated bearings installed to eliminate circulating bearing
currents. To minimize DE (drive end) bearing and shaft
currents, proper grounding of the frequency converter,
motor, driven machine, and motor to the driven machine is
required.
Standard mitigation strategies:
1. Use an insulated bearing.
2. Apply rigorous installation procedures.
2a
2b
2c
2d
2e
2f
3. Lower the IGBT switching frequency.
28
®
VLT
Motor insulation
Standard U = 1300 V
LL
Reinforced U = 1600 V
LL
Reinforced U = 1800 V
LL
Reinforced U = 2000 V
LL
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
frequency converter. Achieve that for
example by using a screened cable
which has a 360° connection in the
motor and the frequency converter.
Make sure that the impedance from
frequency converter to building ground
is lower than the grounding impedance
of the machine. This can be difficult for
pumps.
Make a direct ground connection
between the motor and load motor.
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Plus Panel
4. Modify the inverter waveform, 60° AVM versus
SFAVM.
5. Install a shaft grounding system or use an
isolating coupling.
6. Apply conductive lubrication.
7. Use minimum speed settings if possible.
8. Try to ensure that the line voltage is balanced to
ground. This can be difficult for IT, TT, TN-CS or
grounded leg systems.
9. Use a dU/dt or sinus filter.

4.4.3 Control Cable Routing

Tie down all control wires to the designated control cable
routing. To ensure optimum electrical immunity, connect
the screens properly.
Fieldbus connection
Connections are made to the relevant options on the
control card. For details, see the relevant fieldbus
instruction. Place the cable in the provided path inside the
frequency converter and tie it down with other control
wires.
MG13B102