VLT ® 2000 Series I EMC correct installation A number of factors must be considered in order to achieve EMC correct installation of the VLT 2000 frequency converter. Cable for serial communication: The cable for serial communication should be screened. The screen should be installed using a screen clamp on the VLT frequency converter (see the instruction for installation, page 10, point B ). Installation I General The basic VLT 2000 units do not comply with any EMC emission specifications, since no EMC filter (RFI filter) is incorporated in the basic units. Therefore it is necessary to install an RFI and motor filter module to comply with EMC emission specifications.
VLT Series 2000 is available with built-in RFI filter that fulfils the EMC emission requirements. In addition to reducing the mains interference, the fil- ters also reduce the interference radiating from the unscreened motor cable. As far as the motor cable is concerned, only interference above 30 MHz is reduced (ref. EN 55011-1A). Motor cable: For the motor either screened or unscreened cable can be used. In connection with installation of the RFI and motor filter module it is recommended to use unscreened motor cable. With screened motor cable, the screen must be installed under the cable clamp on the cable relief fitting.
Mounting with twisted screen ends (Pigtails) should be avoided as this will destroy the screen effect at high frequences. In principle the motor cable screen may not be interrupted and it may not be earth connected. If it is necessary to interrupt the screen to mount a motor starter or motor relays, the screen must continue with an impedance which is as low as possible. The EMC emission specifications are complied with by using up to 100 m of unscreened motor cable. If screened cable is used the demand for conducted noise (150 kHz - 30 MHz) cannot be observed.
Section 1 Section 2 Section 3 To reduce the electromagnetic noise level from the to- tal system as far as possible (frequency converter and motor installation), it is important to make the motor and brake cables as short as possible. Cables having a sensitive noise level may not be led together with motor and brake cables. I How to install Units with RFI and motor filter module: When the RFI and motor filter module is installed it is recommended to use unscreened motor cable, since this gives the lowest electromagnetic noise level. Brake cable: Screened cable must be used for the brake resistor. The screen must be installed under the cable clamp on the cable relief fitting.
(See page 10 point E ). Avoid using screen pigtails. Use brake cable lengths of up to 5 m. Control cable: The control cable must be screened. The screen must be installed under the screen clamp on the screen termination bracket. Mounting with twisted screen ends (Pigtails) should be avoided, as this will destroy the screen effect at high frequencies. Normally, the screen should also be connected to the base of the controlling appliance (follow the instructions for use of the appliance in question). In connection with very long control cables and analogue signals, 50 Hz ripple loops may occur in rare cases, depending on the installation.
This is because of interference coupling from the mains supply cables. In this connection it can be necessary to break the screen or possible insert a 100nF con- denser between screen and base. Sensitive signal cables: Cables having a sensitive noise level may not be led together with motor and brake cables. Equalising currents: Efforts should be made to avoid possible equalising currents that may occur when the control cable screen is connected to the base (earthed) at both ends. Equalising currents occur because of voltage differences between the VLT frequency converter base and the base of the controlling appliance.
They can be avoided by making a tight fit with the cabinet base rear plate, thereby ensuring that any equalising currents will run via the base rear plates and their joints, not via the cable screens. MG.20.B6.02 – VLT is a registered Danfoss trademark 9