01/02 AWB8230-1413GB
Electrical connection
37
Motor cable
To ensure electromagnetic compatibility, use only screened motor
cables. The length of the motor cable and the associated use of
further components has an influence on the motor control mode
and the performance characteristics. In parallel operation (multiple
motors connected to the frequency inverter output), the resulting
cable lengths
l
res
must be calculated:
l
res
=
S
l
M
x
W
n
M
S
l
M
:
Sum of all motor cable lengths
n
M
:
Number of motor circuits
Keep the motor cables as short as possible as it will positively
influence the drive’s characteristics.
Motor choke, d
u
/d
t
filters, sinusoidal filters
Motor chokes compensate for capacitive currents with long motor
cables and with grouped drives (multiple connection of parallel
drives to a single inverter).
The use of motor chokes is recommended (observe the
manufacturers instructions):
• for grouped drives
• for the operation of three-phase current asynchronous motors
with maximum frequencies greater than 200 Hz,
• for the operation of reluctance motors or permanently excited
synchronous motors with maximum frequencies above 120 Hz.
d
u
/d
t
filters are used for limiting the rate of voltage rise at the
motor terminals to values below 500 V/
m
s. They should be applied
for all motors with unknown or insufficient insulation withstand
voltage.
When sinusoidal filters are used, the motor supply voltage and
current are almost sinusoidal.
Bypass operation
If you want to have the option of operating the motor with the
frequency inverter or directly from the mains supply, the incoming
supplies must be mechanically interlocked:
h
With long motor cables, the leakage currents caused by
parasitic cable capacities can cause the “earth fault”
message. In this case, motor filters must be used.
Caution!
During the engineering phase, keep in mind that the
voltage drop across motor filters and d
u
/d
t
filters can be
up to 4 % of the frequency inverter’s output voltage.
Caution!
During the engineering phase, keep in mind that the
sinusoidal filter must be matched to the output voltage
and to the frequency inverter’s pulse frequency.
The voltage drop on the sinusoidal filter can be up to
15 % of the frequency inverter’s output voltage.
Caution!
A changeover between the frequency inverter and the
mains supply must take place in a voltage-free state.
Warning!
The frequency inverter outputs (U, V, W) must not be
connected to the mains voltage (destruction of the device,
risk of fire).
Figure 32:
Bypass motor control
Q1
I> I> I>
K1M
S1
M1
G1
M
3
h
L1 L2 L3
L1 L2 L3
U V W
efesotomasyon.com - Klockner Moeller - inverter
