3.4.15 Motor Insulation
For motor cable lengths ≤ the maximum cable length
listed in chapter 5.4 Cable Specications, the motor
insulation ratings in Table 3.28 are recommended. Peak
voltage can be up to twice the DC-link voltage, and 2.8
times the mains voltage, due to transmission line eects in
the motor cable. If a motor has lower insulation rating, use
a dU/dt or sine-wave lter.
Nominal mains voltage [V] Motor insulation [V]
U
N
≤420
Standard U
LL
=1300
420<U
N
≤500 Reinforced U
LL
=1600
500<U
N
≤600 Reinforced U
LL
=1800
600<U
N
≤ 690 Reinforced U
LL
=2000
Table 3.28 Motor Insulation Ratings
3.4.16 Motor Bearing Currents
All motors installed with VLT
®
AutomationDrive FC 302
frequency converters with a power rating of 250 kW or
higher must have NDE (Non-Drive End) insulated bearings
installed to eliminate circulating bearing currents. To
minimize DE (Drive End) bearing and shaft currents, ensure
that the frequency converter, motor, driven machine, and
motor to the driven machine are grounded properly.
Standard mitigation strategies:
1. Use an insulated bearing.
2. Apply rigorous installation procedures.
2a Ensure that the motor and load motor
are aligned.
2b Strictly follow the EMC installation
guideline.
2c Reinforce the PE so the high frequency
impedance is lower in the PE than the
input power leads.
2d Provide a good high frequency
connection between the motor and the
frequency converter, for example by
using shielded cable which has a 360°
connection in the motor and the
frequency converter.
2e Make sure that the impedance from the
frequency converter to the building
ground is lower than the grounding
impedance of the machine.
2f 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 where possible.
8. Ensure that the mains voltage is balanced to
ground.
9. Use a dU/dt or sine-wave lter.
3.4.17 Brake Resistor Temperature Switch
•
Torque: 0.5–0.6 Nm (5 in-lb)
•
Screw size: M3
This input can be used to monitor the temperature of an
externally connected brake resistor. If the input between
104 and 106 is established, the frequency converter trips
on warning/alarm 27 Brake IGBT. If the connection is closed
between 104 and 105, the frequency converter trips on
warning/alarm 27 Brake IGBT.
Install a KLIXON switch that is normally closed. If this
function is not used, short circuit 106 and 104 together.
•
Normally closed: 104–106 (factory installed
jumper)
•
Normally open: 104–105
Terminal number Function
106, 104, 105 Brake resistor temperature switch.
Table 3.29 Brake Resistor Temperature Switch Terminals
CAUTION
MOTOR COASTING
If the temperature of the brake resistor gets too high
and the thermal switch drops out, the frequency
converter stops braking and the motor starts coasting.
175ZA877.10
106
NC
104
C
105
NO
Illustration 3.47 Brake Resistor Temperature Switch
How to Install Operating Instructions
MG34Q402 Danfoss A/S © 04/2016 All rights reserved. 51
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