Lenze EDB9300UES User Manual
Page 87
Transport, Installation and Connection
82
BA8230
•
If contactors, motor protection switches or terminals are located on the screened
motor cable, the screens of the cables connected at that point are to be continuous
and of low impedance. In the motor terminal box the screen is to be connected with
the PE / PA. Metal cable screw connections (nickel plated brass) at the metal
connection box (do not use a plastic connection box) provides a very good
connection between the screen and the motor casing. On the inverter side the
screen is to be connected to the central screen rail and not directly to the unit.
•
For reasons of EMC the motor cable should be as short as possible. The frequency
inverter should preferably be located close to the motor.
Additional radio interference suppression measures may be necessary in systems
which are physically very large, depending on the situation. In particular
improvements in potential compensation may be necessary.
The motor cable lengths stated in this section were calculated on the basis of trials
and are the maximum guideline values with regard to the inphase current occurring.
The inphase current limits the dynamics and causes additional losses in the
inverter. With dynamic direction changes at the zero crossover point it may be
necessary to adjust some control parameters when commissioning drives without
speed actual value detection, due to longer cables.
•
Analog and digital control leads for the 8230 frequency inverter control electronics
and data leads are to be laid using screened cable. The screen is to be connected
firmly at both ends for good potential compensation. Good potential compensation
will be achieved if a star or grid type earth system is used consistently. Applying the
screen twice on short spacing distances in the cubicle increases the interference
resistance. When transferring analog signals of low amplitudes in the mV range a
single-sided application of the screen in the switchgear cubicle may only be
necessary close to strong radiation fields, due to a low frequency “50 Hz hum”.
Generally cable screens are always connected at both ends. This is the only way to
ensure good interference resistance at high frequencies throughout the entire
range of interference frequencies. Without potential compensation the screen on
control cables should only be connected at one end, however, but this is always a
compromise. The cable screens are to be applied directly after they enter the
cubicle, as this is where the highest interference amplitudes occur. Apply the
screen generously to the screen / protective conductor rail and secure the screen
with cable clamps, screen connection terminals or hose clamps, depending on the
system involved. Continue the screen up to the terminal strip or, if necessary, up to
the assembly at the 8230 frequency inverter or external modules, without any
interruptions. The internal screen contacting facilities on the aluminium slide-in rack
for the control electronics, which use round clamps, are always to be used for
making contact with the screen. So-called "pigtails” or similar must never be used
for control leads. Such a path would be low impedance and the flow of the screen
current close to signal conductors would allow the screen current to act as an
interference current. The cable screen must always be connected directly at the
end.
The cables at the 8230 frequency inverter terminal block are to be divided into
analog input and output cables and digital input and output cables and these
groups are to be laid separately using screened cables with both ends of the
screen connected. Alternatively a double screen control / data cable is possible. In
this case the outer screen is earthed to the side of the unit and the inner screen is
earthed at the other end. As these cables generally have screens made of foil,
mechanical damage can occur easily, even with just slight bending and pressure.
An additional compensation cable is always particularly recommended if the
potential difference between the relevant earthing points is > 5 V. 25 mm² Cu is
sufficient as an equalizer up to acable of 200 m. For longer cables, at least 35 mm²
Cu are recommended.
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