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General information about electrical installation
High voltage warning
The voltage of the frequency converter
is dangerous whenever the equipment is
connected to mains. Incorrect installation
of the motor or the frequency converter may cause
damage to the equipment, serious personal injury
or death. Consequently, the instructions in this
Design Guide, as well as national and local safety
regulations, must be complied with. Touching
the electrical parts may be fatal - even after
disconnection from mains: Using VLT 7002-7005,
380-460 V wait at least 4 minutes
Using VLT 7006-7072, 380-460 V wait at
least 15 minutes
NB!:
It is the user's or certified electrician's
responsibility to ensure correct earthing and
protection in accordance with applicable
national and local norms and standards.
Earthing
The following basic issues need to be considered
when installing a frequency converter, so as to obtain
electromagnetic compatibility (EMC).
•
Safety earthing: Please note that the frequency
converter has a high leakage current and must
be earthed appropriately for safety reasons.
Apply local safety regulations.
•
High-frequency earthing: Keep the earth wire
connections as short as possible.
Connect the different earth systems at the lowest
possible conductor impedance. The lowest possible
conductor impedance is obtained by keeping the
conductor as short as possible and by using the
greatest possible surface area. A flat conductor, for
example, has a lower HF impedance than a round
conductor for the same conductor cross-section
C
. If more than one device is installed in cabinets,
VESS
the cabinet rear plate, which must be made of
metal, should be used as a common earth reference
plate. The metal cabinets of the different devices
are mounted on the cabinet rear plate using the
lowest possible HF impedance. This avoids having
different HF voltages for the individual devices and
avoids the risk of radio interference currents running
in connection cables that may be used between
the devices. The radio interference will have been
reduced. In order to obtain a low HF impedance, use
the fastening bolts of the devices as HF connection
MG.70.A1.02 - VLT is a registered Danfoss trademark
VLT® 7000 Booster
to the rear plate. It is necessary to remove insulating
paint or similar from the fastening points.
Cables
Control cables and the filtered mains cable should
be installed separate from the motor cables so as to
avoid interference overcoupling. Normally, a distance
of 20 cm will be sufficient, but it is recommended
to keep the greatest possible distance wherever
possible, especially where cables are installed in
parallel over a substantial distance.
With respect to sensitive signal cables, such as
telephone cables and data cables, the greatest possible
distance is recommended with a minimum of 1 m per 5
m of power cable (mains and motor cable). It must be
pointed out that the necessary distance depends on
the sensitivity of the installation and the signal cables,
and that therefore no precise values can be stated.
If cable jaws are used, sensitive signal cables are not
to be placed in the same cable jaws as the motor
cable or brake cable. If signal cables are to cross
power cables, this should be done at an angle of
90 degrees. Remember that all interference-filled
in- or outgoing cables to/from a cabinet should
be screened/armoured or filtered.
See also EMC-correct electrical installation.
Screened/armoured cables
The screen must be a low HF-impedance screen.
This is ensured by using a braided screen of
copper, aluminium or iron. Screen armour intended
for mechanical protection, for example, is not
suitable for an EMC-correct installation. See
also Use of EMC-correct cables.
Extra protection with regard to indirect contact
ELCB relays, multiple protective earthing or earthing can
be used as extra protection, provided that local safety
regulations are complied with. In the case of an earth
fault, a DC content may develop in the faulty current.
Never use ELCB relays, type A, since such relays
are not suitable for DC fault currents.
If ELCB relays are used, this must be:
•
Suitable for protecting equipment with a direct
current content (DC) in the faulty current
(3-phase bridge rectifier)
•
Suitable for power-up with short charging
current to earth
•
Suitable for a high leakage current
25
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