Brake Resistor Temperature Switch; Motor Insulation; Motor Bearing Currents - Danfoss VLT AQUA Drive FC 202 Operating Instructions Manual

Electrical Installation
The connection cable to the brake resistor must be
screened and the max. length from frequency converter to
the DC bar is limited to 25 m.
Terminal No. Function
81, 82 Brake resistor terminals
Table 4.3 Terminal Functions
The connection cable to the brake resistor must be
screened. Connect the screen with cable clamps to the
conductive back plate of the frequency converter and the
metal cabinet of the brake resistor.
Size the brake cable cross-section to match the brake
torque. See also Brake Instructions for further information
regarding safe installation.
WARNING
Note that voltages up to 790 V DC, depending on the
supply voltage, are possible on the terminals.
F-frame requirements
The brake resistors must be connected to the brake
terminals in each inverter module.

4.6.3 Brake Resistor Temperature Switch

The input for the brake resistor temperature switch can be
used to monitor the temperature of an externally
connected brake resistor. If the connection between 104
and 106 is removed, the frequency converter trips on
warning/alarm 27, Brake IGBT.
Install a Klixon switch that is 'normally closed' in series
with the existing connection on either 106 or 104. Any
connection to this terminal must be double insulated
against high voltage to maintain PELV.
Normally closed: 104–106 (factory installed jumper).
Terminal No. Function
106, 104, 105 Brake resistor temperature switch.
Table 4.4 Terminal Functions
CAUTION
If the temperature of the brake resistor is too high and
the thermal switch drops out, the frequency converter
stops braking. The motor coasts.
106 104
NC C
Illustration 4.4 Factory-installed Jumper
MG21B202
Operating Instructions
105
NO
Danfoss A/S © Rev. 2014-01-22 All rights reserved.

4.6.4 Motor Insulation

For motor cable lengths ≤ the maximum cable length, the
motor insulation ratings listed in Table 4.5 are
recommended. The peak voltage can be twice the DC-link
voltage or 2.8 times mains voltage, due to transmission
line effects in the motor cable. If a motor has lower
insulation rating, use a dU/dt or sine wave filter.
Nominal Mains Voltage Motor Insulation
≤ 420 V
U Standard U
N
420 V < U ≤ 500 V Reinforced U
N
Table 4.5 Recommended Motor Insulation Ratings

4.6.5 Motor Bearing Currents

Motors with a rating 110 kW or higher combined with
frequency converters are best with NDE (Non-Drive End)
insulated bearings to eliminate circulating bearing currents
caused by motor size. To minimise DE (Drive End) bearing
and shaft currents, proper grounding is required for:
•
Frequency converter
•
Motor
•
Motor-driven machine
•
Motor to the driven machine
Although failure due to bearing currents is infrequent, use
the following strategies to reduce the likelihood:
•
Use an insulated bearing
•
Apply rigorous installation procedures
•
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
•
Ensure that the impedance from frequency
converter to building ground 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 line voltage is balanced to
ground.
•
Use an insulated bearing as recommended by the
motor manufacturer (note: Motors from reputable
manufacturers typically have insulated bearings
as standard in motors of this size)
4
= 1,300 V
LL
= 1,600 V
LL
31
4