GE AF-600 FP Design And Installation Manual

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Contents

7 Installation Consideration7.1 General Aspects of EMC7.1.1 General Aspects of EMC EmissionsElectrical interference is usually conducted at frequenciesin the range of 150 kHz to 30 MHz. Airborne interferencefrom the drive system in the range 30 MHz to 1 GHz isgenerated from the inverter, motor cable, and the motor.As shown in the figure below, capacitive currents in themotor cable coupled with a high dV/dt from the motorvoltage generate leakage currents.The use of a shielded motor cable increases the leakagecurrent (see figure below), because shielded cables havehigher capacitance to ground than non-shielded cables. Ifthe leakage current is not filtered, it will cause greaterinterference on the line power in the radio frequencyrange below approximately 5 MHz. Since the leakagecurrent (I1 ) is carried back to the unit through the shield (I3 ), there will in principle only be a small electro-magneticfield (I4 ) from the shielded motor cable according to thebelow figure.The shield reduces the radiated interference but increasesthe low-frequency interference on line power. The motorcable shield must be connected to the adjustablefrequency drive enclosure as well as on the motorenclosure. This is best done by using integrated shieldclamps so as to avoid twisted shield ends (pigtails). Theseincrease the shield impedance at higher frequencies, whichreduces the shield effect and increases the leakage current(I4 ).If a shielded cable is used for networknetwork, relay,control cable, signal interface and brake, the shield mustbe mounted on the enclosure at both ends. In somesituations, however, it will be necessary to break the shieldto avoid current loops.Figure 7.1If the shield is to be placed on a mounting plate for theadjustable frequency drive, the mounting plate must bemade of metal, because the shield currents have to beconveyed back to the unit. Moreover, ensure goodelectrical contact from the mounting plate through themounting screws to the adjustable frequency driverchassis.When non-shielded cables are used, some emissionrequirements are not complied with, although theimmunity requirements are observed.In order to reduce the interference level from the entiresystem (unit + installation), make motor and brake cablesas short as possible. Avoid placing cables with a sensitivesignal level alongside motor and brake cables. Radiointerference higher than 50 MHz (airborne) is especiallygenerated by the control electronics.Installation Consideration AF-600 FP Design and Installation GuideDET-768A 7-17 7