Hi folks. I need some help in the following issue:
We use in our machines adjustable speed power drive systems. They are synthesizing a three phase sine wave by PWM. They have a very high disturbance potential, especially from the cable to the motor. If this cable is shielded and the shield is correctly bonded at both ends, the disturbances induced in other are usually below the limits. It is very important to bond the shield correctly. Now the problem: Some times it is necessary (for safety reasons) to galvanically disconnect the motor from the drive system. At that point disturbances are created because: - an impedance is added to the shield path (return path for HF), thus dramatically reducing the effectiveness of the shield. - the inner conductor build a radiating loop - disturbances are coupled into the coil of the contactor an thus spread into the machine - disturbances are coupled in the wires to the auxiliary contacts - disturbances are coupled in other wires in the neighborhood A possible solution would be a contactor having the power contacts in a shielded enclosure and the coil and the auxiliary contacts outside the shielded enclosure. [ see http://ourworld.compuserve.com/homepages/dancau/contacto.htm for image] DOES ANYBODY KNOW A SUPPLIER FOR SUCH CONTACTORS ? Another possible solution would be to place the contactor in a shielded enclosure, bond the shield to the enclosure and to filter all wires going in and out (to the coil and to the auxiliary contacts). My experience shows that the requirements to the filter for the coil are very high. and thus expensive. Any comments on this issue are welcome. Thanks in advance George -- ************************************************************** * Dr. Georg M. Dancau * HAUNI MASCHINENBAU AG * * [email protected] * Manager EMC Lab * * TEL: +49 40 7250 2102 * Kampchaussee 8..32 * * FAX: +49 40 7250 3801 * 21027 Hamburg, Germany * ************************************************************** * home: Tel: +49 4122 99451 * Hauptstr. 60a * * Fax: +49 4122 99454 * 25492 Heist, Germany * **************************************************************
