Motor Insulation; Motor Bearing Currents; Installation Of Misc. Connections - Danfoss VLT HVAC Drive FC 102 Design Manual

How to Install
Protection, set to [20] ATEX ETR, is combined with the use
of MCB 112, it is possible to control an Ex-e motor in
explosion hazardous areas. Consult the Programming Guide
for details on how to set up the frequency converter for
safe operation of Ex-e motors.

5.4.11 Motor Insulation

For motor cable lengths ≤ the maximum cable length
listed in chapter 8 General Specifications and Trouble-
shooting, the recommended motor insulation ratings are in
5 5
Table 5.25. 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
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 5.25 Motor Insulation at Various Nominal Mains Voltages

5.4.12 Motor Bearing Currents

For motors with a rating 110 kW or higher operating via
frequency converters, use NDE (Non-Drive End) insulated
bearings to eliminate circulating bearing currents due to
the physical size of the motor. To minimise 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 rare, if it occurs, use the following
mitigation strategies.
Standard mitigation strategies
•
Use an insulated bearing
•
Apply rigorous installation procedures
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152
Design Guide
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 by screened cable.
The cable must have a 360° connection
in the motor and frequency converter
Ensure that the impedance from
frequency converter to building ground
Danfoss A/S © Rev. 05/2014 All rights reserved.
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 mains voltage is balanced
to ground. Balancing to ground can be difficult
for IT, TT, TN-CS or Grounded leg systems
•
Use an insulated bearing as recommended by the
motor manufacturer
NOTICE
Motors from reputable manufacturers typically have
insulated bearings fitted as standard in motors of this
size.
If none of these strategies works, consult the factory.
If necessary, after consulting 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

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.
RS 232
USB
RS 485
Illustration 5.101 RS-485 Connecting Multiple Frequency
Converters to Master
In order to avoid potential equalizing currents in the
screen, ground the cable screen via terminal 61, which is
connected to the frame via an RC-link.
68 69 68 69 68 69
+
-
MG16C202