However, the overall efficiency of VFDs are highly dependent on their installation and the quality of equipment used during the design process. The motor, the cables and any other connected devices should be completely compatible with the specifications of the drive to be installed.
VFDs are an essential of solid state technology, and convert 3-phase AC line voltage to sinusoidal PWM waveform, through which frequency and voltage can be varied. Internally, VFDs are made up of:
The inverter is responsible for a smooth stream of variable voltage and frequency output which would then drive the motor. To ensure centralized control, a microprocessor is installed in the VFD, governing the overall operation and parameters.
Before a VFD can be integrated into your system, you should ask yourself a few questions to make sure you select a drive of the right specifications:
Cable-to-motor impedance mismatch can cause reflected waves in VFDs, effectively doubling the voltage level which can result in damaged cables and components. The preferred solution is use of XLPE Cable Insulation which can withstand such reflected waves, compared to PVC which are dangerous in such applications. The use of such cables also has other benefits for the VFD system such as reduced capacitance which can improve the motor’s life. The thermal isolation property also ensures heat generated from corona losses do not affect other equipment or lead to hazards such as insulation meltdown or fires.
In addition, a VFD cable radiates noise, which is proportional to the amount of electric current varying within it. As the length of the cable grows, so does the noise, and therefore proper shielding of such a cable is required. If left unrectified, the radiated noise can cause problems such as capacitive coupling between motor windings and frame affecting nearby devices such as thermocouples, encoders, as well as low-level communication signals.
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