Residual Current Devices (Rcd) And Insulation Resistance Monitor (Irm); Leakage Current - Danfoss VLT AutomationDrive FC 361 Series Design Manual

Electrical Installation Con...
7.6.3 Motor Insulation
For motor cable lengths that are less than or equal to the
maximum cable length listed in chapter 5.5 Cable Specifi-
cations, use the motor insulation ratings shown in
Table 7.10. If a motor has lower insulation rating, Danfoss
recommends using a dU/dt or sine-wave filter.
Nominal mains voltage Motor insulation
≤420 V
U Standard U
N
≤500 V
Reinforced U
420 V<U
N
≤600 V
500 V<U Reinforced U
N
≤690 V
600 V<U Reinforced U
N
Table 7.10 Motor Insulation Ratings
7.6.4 Motor Bearing Currents
To eliminate circulating bearing currents in all motors
installed with the drive, install NDE (non-drive end)
insulated bearings. To minimize DE (drive end) bearing and
shaft currents, ensure proper grounding of the drive,
motor, driven machine, and motor to the driven machine.
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.
-
Provide a good high-frequency
connection between the motor and the
drive. Use a shielded cable that has a
360° connection in the motor and the
drive.
-
Ensure that the impedance from the
drive to building ground is lower than
the grounding impedance of the
machine. This procedure can be difficult
for pumps.
-
Make a direct ground connection
between the motor and load motor.
•
Lower the IGBT switching frequency.
•
Modify the inverter waveform, 60° AVM vs.
SFAVM.
•
Install a shaft grounding system or use an
isolating coupling.
•
Apply conductive lubrication.
•
Use minimum speed settings if possible.
MG06K102
Design Guide
7.7 Residual Current Devices (RCD) and
Use RCD relays, multiple protective grounding, or
grounding as extra protection, provided they comply with
=1300 V
LL
local safety regulations.
=1600 V
LL
If a ground fault appears, a DC current can develop in the
=1800 V
LL faulty current. If RCD relays are used, local regulations
=2000 V
must be observed. Relays must be suitable for protection
LL
of 3-phase equipment with a bridge rectifier and for a brief
discharge on power-up. See chapter 7.8 Leakage Current for
more details.

7.8 Leakage Current

Follow national and local codes regarding protective
grounding of equipment where leakage current exceeds
3.5 mA.
Drive technology implies high-frequency switching at high
power. This high-frequency switching generates a leakage
current in the ground connection.
The ground leakage current is made up of several contri-
butions and depends on various system configurations,
including:
Leakage current
Illustration 7.11 Motor Cable Length and Power Size Influence
the Leakage Current. Power Size a > Power Size b.
The leakage current also depends on the line distortion.
Danfoss A/S © 03/2019 All rights reserved.
•
Try to ensure that the mains voltage is balanced
to ground. This procedure can be difficult for IT,
TT, TN-CS, or grounded leg systems.
•
Use a dU/dt or sine-wave filter.
Insulation Resistance Monitor (IRM)
•
RFI filtering.
•
Motor cable length.
•
Motor cable shielding.
•
Drive power.
7 7
a
b
Motor cable length
47