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52 Planning the electrical installation
Resistor braking of the drive
Note 7:
When the drive is in braking mode for a large part of its operation time, the
intermediate circuit DC voltage of the drive increases, the effect being similar to
increasing the supply voltage by up to 20 percent. The voltage increase should be
taken into consideration when determining the motor insulation requirement.
Example: Motor insulation requirement for a 400 V application must be selected as if
the drive were supplied with 480 V.
Drives with an IGBT supply unit
Note 8:
If voltage is raised by the drive (this is a parameter selectable function), select the
motor insulation system according to the increased intermediate circuit DC voltage
level, especially in the 500 V supply voltage range.
Calculating the rise time and the peak line-to-line voltage
Note 9:
The peak line-to-line voltage at the motor terminals generated by the drive as well as
the voltage rise time depend on the cable length. The requirements for the motor
insulation system given in the table are "worst case" requirements covering
installations with 30 m and longer cables. The rise time can be calculated as follows:
Û
u
t = 0.8 ·
/(d
/d
LL
values of the graph by the supply voltage (
unit or resistor braking, the
3.0
2.5
2.0
1.5
1.0
0.5
0.0
100
With du/dt Filter
Note 10: Sine filters protect the motor insulation system. Therefore, d
be replaced with a sine filter. The peak phase-to-phase voltage with the sine filter is
approximately 1.5 ×
t
Û
u
). Read
and d
LL
Û
u
and d
LL
Û
/U
LL
N
du/dt
------------ - (1/s)
U
N
200
300
Cable length (m)
U
.
N
t
/d
from the diagrams below. Multiply the
U
). In case of drives with an IGBT supply
N
t
/d
values are approximately 20% higher.
5.5
5.0
du/dt
------------ - (1/s)
U
4.5
N
4.0
3.5
3.0
2.5
2.0
1.5
1.0
100
Without du/dt Filter
Û
/U
LL
N
200
300
Cable length (m)
u
t
/d
filter can
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