Brake Cable; Motor Insulation; Motor Bearing Currents - Danfoss VLT FC 102 Operating Instructions Manual

Electrical Installation
Motor
U V W
2 2 2
U V
W
1 1 1
FC
96 97 98
Motor
U V W
2 2 2
U V W
1 1 1
FC
96 97 98
Illustration 4.3 Motor Rotation Check
F-frame requirements
Use motor phase cables in quantities of 2, resulting in 2, 4,
6, or 8 to obtain an equal number of wires on both
inverter module terminals. The cables are required to be
equal length within 10% between the inverter module
terminals and the first common point of a phase. The
recommended common point is the motor terminals.
Output junction box requirements
The length, minimum 2.5 m, and quantity of cables must
be equal from each inverter module to the common
terminal in the junction box.
NOTICE
If a retrofit application requires an unequal number of
wires per phase, consult the factory or use the top/
bottom entry side cabinet option instruction.

4.6.2 Brake Cable

Frequency converters with factory installed brake chopper
option.
(Only standard with letter B in position 18 in the type
code).
MG16I302
Operating Instructions
The connection cable to the brake resistor must be
screened and the maximum length from frequency
converter to the DC bar is limited to 25 m.
Terminal number
81, 82
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.
WARNING
Note that voltages up to 790 V DC, depending on the
supply voltage, are possible on the terminals.
F-frame requirements
Connect the brake resistors to the brake terminals in each
inverter module.

4.6.3 Motor Insulation

For motor cable lengths ≤ the maximum cable length, the
motor insulation ratings listed in Table 4.4 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
≤420 V
U
N
420 V<U
Table 4.4 Recommended Motor Insulation Ratings

4.6.4 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:
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•
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Function
Brake resistor terminals
Motor insulation
Standard U
≤500 V Reinforced U
N
The frequency converter.
The motor.
Motor-driven machine.
Motor to the driven machine.
4
=1300 V
LL
=1600 V
LL
39
4