Danfoss VLT AQUA Design Manual

Also see for vlt aqua: Instructions Design guide Instruction manual Operating instructions Operating instructions

Contents

5.2.6. Electrical Installation of Motor CablesScreening of cablesAvoid installation with twisted screen ends (pigtails). They spoil the screening effect at higher frequencies.If it is necessary to break the screen to install a motor isolator or motor contactor, the screen must be continued at the lowest possible HF impedance.Cable length and cross-sectionThe frequency converter has been tested with a given length of cable and a given cross-section of that cable. If the cross-section is increased, the cablecapacitance - and thus the leakage current - may increase, and the cable length must be reduced correspondingly.Switching frequencyWhen frequency converters are used together with Sine-wave filters to reduce the acoustic noise from a motor, the switching frequency must be setaccording to the Sine-wave filter instruction inPar. 14-01.Aluminium conductorsAluminium conductors are not recommended. Terminals can accept aluminium conductors but the conductor surface has to be clean and the oxidationmust be removed and sealed by neutral acid free Vaseline grease before the conductor is connected.Furthermore, the terminal screw must be retightened after two days due to the softness of the aluminium. It is crucial to keep the connection a gas tightjoint, otherwise the aluminium surface will oxidize again.5.2.7. FusesBranch circuit protection:In order to protect the installation against electrical and fire hazard, all branch circuits in an installation, switch gear, machines etc., must be shortcircuitand overcurrent protected according to the national/international regulations.Short circuit protection:The frequency converter must be protected against short-circuit to avoid electrical or fire hazard. Danfoss recommends using the fuses mentioned intables 5.3 and 5.4 to protect service personnel or other equipment in case of an internal failure in the unit. The frequency converter provides full shortcircuit protection in case of a short-circuit on the motor output.Over-current protection:Provide overload protection to avoid fire hazard due to overheating of the cables in the installation. Over current protection must always be carried outaccording to national regulations. The frequency converter is equipped with an internal over current protection that can be used for upstream overloadprotection (UL-applications excluded). See par. 4-18. Fuses must be designed for protection in a circuit capable of supplying a maximum of 100,000A rms (symmetrical), 500 V/600 V maximum.Non UL complianceIf UL/cUL is not to be complied with, Danfoss recommends using the fuses mentioned in table 5.2, which will ensure compliance with EN50178:In case of malfunction, not following the recommendation may result in unnecessary damage to the frequency converter.5. How to Install VLT® AQUA Drive Design Guide88 MG.20.N3.02 - VLT® is a registered Danfoss trademark5