Installation Of Misc. Connections - Danfoss VLT Design Manual

How to Install
5.4.7 Motor Insulation
For motor cable lengths ≤ the maximum cable length
listed in the General Specifications tables the following
motor insulation ratings are recommended because 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. If a motor has lower insulation rating it
recommended to use a du/dt or sine wave filter.
Nominal Mains Voltage Motor Insulation
≤ 420 V
Standard U
U
N
420 V < U ≤ 500 V Reinforced U
N
500 V < U ≤ 600 V Reinforced U
N
Table 5.16
5.4.8 Motor Bearing Currents
It is recommended that motors of a rating 110 kW or
higher operating via frequency converters should have
NDE (Non-Drive End) insulated bearings installed to
eliminate circulating bearing currents due to the physical
size of the motor. 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. Although failure due to bearing
currents is low and dependent on many different items, for
security of operation the following are mitigation strategies
which can be implemented.
Standard mitigation strategies
1. Use an insulated bearing
2. Apply rigorous installation procedures
Ensure 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
for instance by 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 that the
grounding impedance of the machine. This can
be difficult for pumps- Make a direct earth
connection between the motor and load motor.
3. Apply conductive lubrication
4. Try to ensure that the line voltage is balanced to
ground. This can be difficult for IT, TT, TN-CS or
Grounded leg systems
®
VLT Refrigeration Drive Design Guide
NOTE
Motors from reputable manufacturers will typically have
these fitted as standard in motors of this size.
If found to be necessary and after consultation with
Danfoss:
= 1300 V
LL
= 1600 V
LL
= 1800 V
LL

5.5 Installation of Misc. Connections

5.5.1 RS-485 Bus Connection
One or more frequency converters can be connected to a
control (or master) using the RS-485 standardized interface.
Terminal 68 is connected to the P signal (TX+, RX+), while
terminal 69 is connected to the N signal (TX-, RX-).
If more than one frequency converter is connected to a
master, use parallel connections.
Illustration 5.29
In order to avoid potential equalizing currents in the
screen, earth the cable screen via terminal 61, which is
connected to the frame via an RC-link.
For EMC correct installation, refer to .
Bus termination
The RS-485 bus must be terminated by a resistor network
at both ends. For this purpose, set switch S801 on the
control card for "ON".
For more information, see 5.2.13 Switches S201, S202, and
S801.
Communication protocol must be set to 8-30 Protocol.
®
MG16G102 - VLT is a registered Danfoss trademark
5. Use an insulated bearing as recommended by the
motor manufacturer
6. Lower the IGBT switching frequency
7.
Modify the inverter waveform, 60° AVM vs.
SFAVM
8. Install a shaft grounding system or use an
isolating coupling between motor and load
9. Use minimum speed settings if possible
10. Use a dU/dt or sinus filter
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