Motor Insulation; Motor Bearing Currents; Control Cables And Terminals - Danfoss FC 300 Design Manual

8 Electrical Installation

8.5.4 Motor Insulation

For motor cable lengths ≤, the maximum cable length listed in the General
Specifications tables the following motor insulation ratings are recom-
mended because the peak voltage can be up to twice the DC link voltage,
2.8 times the AC line voltage, due to transmission line effects in the motor
cable. If a motor has lower insulation rating, it is recommended to use a
du/dt or sine-wave filter.

8.5.5 Motor Bearing Currents

All motors installed with AutomationDrive FC 302 125 hp [90 kW] or higher power drives 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 drive, motor, driven machine,
and motor to the driven machine is required.
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
8
- 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 for instance by shielded cable which
has a 360° connection in the motor and the adjustable frequency drive.
- Make sure that the impedance from adjustable frequency drive to building ground is lower that the grounding impedance of the machine.
This can be difficult for pumps.
- Make a direct ground connection between the motor and load motor.
3. Lower the IGBT switching frequency
4. Modify the inverter waveform, 60° AVM vs. 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 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

8.6 Control Cables and Terminals

8.6.1 Access to Control Terminals
All terminals to the control cables are located underneath the terminal cover on the front of the adjustable frequency drive. Remove the terminal cover
by means of a screwdriver (see figure).
8-32
Nominal AC Line Voltage
U ≤ 420 V
N
420 V < U ≤ 500 V
N
≤ 600 V
500 V < U
N
≤ 690 V
600 V < U
N
MG.33.BC.22 - VLT ® is a registered Danfoss trademark
FC 300 Design Guide
Motor Insulation
Standard U = 1300 V
LL
Reinforced U = 1600 V
LL
Reinforced U = 1800 V
LL
Reinforced U = 2000 V
LL